razeri_plugin_api/

conformance.rs

// Copyright (C) 2026 Gabriel Shea
// Licensed under either of the Apache License, Version 2.0 or the MIT
// license, at your option.

//! **Every obligation a dialect owes, reported at once.**
//!
//! Two people built dialects against Razeri's authoring guide without help.
//! Between them they met twenty-seven obligations one `cargo test` at a time —
//! a roster fails, you add a row, the next roster fails. Not one of those
//! failures was discoverable before it fired. This module is the report that
//! answers all of them in one pass.
//!
//! # Running it
//!
//! From your own crate's tests, where your dialect is linked and Razeri's
//! registry can see it:
//!
//! ```no_run
//! # use razeri_plugin_api::conformance;
//! # fn example(my_dialect: &dyn razeri_plugin_api::PlatformDialect) {
//! let report = conformance::check(my_dialect);
//! assert!(report.is_clean(), "{report}");
//! # }
//! ```
//!
//! # What it can and cannot see
//!
//! Everything here is read off the dialect object, so it works wherever your
//! plugin compiles: it grades what your dialect declares and what its
//! renderers return. It runs no SQL, so anything only an engine can settle —
//! whether the SQL your dialect emits is the SQL that engine accepts — stays
//! yours to test against a real instance.
//!
//! # Your dialect's name
//!
//! Your platform's names are yours. `DialectInfo::name` is the one Razeri
//! reports, `aliases` is every other spelling a design may use for it, and the
//! resolver reads both off the dialects that are loaded — so the report asks
//! only that your own spellings reach you, and there is no table inside Razeri
//! for your platform to be missing from. The one thing it will tell you is that
//! a spelling you declared is one another loaded platform also answers to,
//! because then the spelling names neither of you.

use crate::PlatformDialect;
use razeri_plugin_contract::{
    ColumnEvolution, ConstraintEnforcement, DataType, DdlRenderer, DialectCapabilities,
    DialectFamily, EntityRef, MergeRestrictions, MergeShape, ProcedureForm, RoutineKind,
    RoutineSpec, ScalarFunctionForm, SliceRef, SliceReplacement, SqlRenderer, StorageRenderer,
    TableFunctionForm, UNKNOWN_PLATFORM,
    data_type::{ArrayDataType, MapDataType, StructDataType, StructField},
    storage_strategy::{
        CompressionStrategy, IndexStrategy, PartitionGranularity, PartitionStrategy, StoragePlan,
    },
};
use std::fmt;

/// How much a finding matters.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum Severity {
    /// **This dialect will produce SQL its engine rejects.** Fix it before
    /// anything else.
    Blocking,
    /// **A question this dialect has not answered.** Razeri has a default and
    /// will use it; the default was written for a different engine.
    Unanswered,
    /// Worth a look. Nothing is broken.
    Note,
}

impl fmt::Display for Severity {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(match self {
            Self::Blocking => "must fix",
            Self::Unanswered => "unanswered",
            Self::Note => "worth a look",
        })
    }
}

/// One thing to fix, in the order a reader wants it: what is wrong, then what
/// to do about it.
#[derive(Debug, Clone)]
pub struct Finding {
    /// How much it matters.
    pub severity: Severity,
    /// One line naming what is wrong.
    pub what: String,
    /// One line naming what to do.
    pub fix: String,
}

/// The whole report for one dialect.
#[derive(Debug, Clone)]
pub struct Report {
    /// The dialect's registry name.
    pub dialect: String,
    /// Everything found, worst first.
    pub findings: Vec<Finding>,
}

impl Report {
    /// Whether nothing blocking or unanswered was found.
    ///
    /// Notes do not fail a report: they are observations, not obligations.
    #[must_use]
    pub fn is_clean(&self) -> bool {
        !self.findings.iter().any(|f| f.severity != Severity::Note)
    }

    /// How many findings of one severity.
    #[must_use]
    pub fn count(&self, severity: Severity) -> usize {
        self.findings.iter().filter(|f| f.severity == severity).count()
    }
}

impl fmt::Display for Report {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let name = &self.dialect;
        if self.findings.is_empty() {
            return writeln!(
                f,
                "{name}: nothing to fix. Every question Razeri asks a dialect, this one answers."
            );
        }
        let blocking = self.count(Severity::Blocking);
        let unanswered = self.count(Severity::Unanswered);
        let notes = self.count(Severity::Note);
        writeln!(f, "{name}: {blocking} to fix, {unanswered} unanswered, {notes} worth a look.")?;
        for finding in &self.findings {
            writeln!(f)?;
            writeln!(f, "  [{}] {}", finding.severity, finding.what)?;
            writeln!(f, "      → {}", finding.fix)?;
        }
        Ok(())
    }
}

/// **The report.** Everything about this dialect that Razeri can check by
/// asking it.
///
/// Registration is checked against the dialects linked into this program. A
/// dialect the host loaded at run time is not among them, so report it with
/// [`check_with_registry`] and the registry it was loaded into.
#[must_use]
pub fn check(dialect: &dyn PlatformDialect) -> Report {
    check_with_registry(dialect, &crate::dialect::PlatformRegistry::with_auto_discovered())
}

/// The same report, against a registry the host built — the path for a dialect
/// loaded at run time rather than linked in.
#[must_use]
pub fn check_with_registry(
    dialect: &dyn PlatformDialect,
    registry: &crate::dialect::PlatformRegistry,
) -> Report {
    let info = dialect.info();
    let mut findings = Vec::new();

    check_registration(&info, registry, &mut findings);
    check_family(info.dialect_family, &mut findings);
    check_required_rendering(dialect, &mut findings);
    check_decisions(dialect, &mut findings);
    check_formula_renderer(dialect, &mut findings);
    check_evolution(dialect, &mut findings);
    check_paired_facts(dialect, &mut findings);

    findings.sort_by_key(|f| f.severity);
    Report { dialect: info.name.to_owned(), findings }
}

/// Every spelling this dialect answers to has to reach this dialect: its own
/// name, and each alias it declares.
///
/// That is the whole obligation, and it is one the author can meet from their
/// own crate — the spellings are the dialect's own, so there is no list inside
/// Razeri to be missing from and nothing here can ask for a change only Razeri
/// could make. What is worth saying is a spelling that reaches somewhere else:
/// one another loaded platform also claims (so it names neither, and Razeri
/// refuses it), or one that reaches a different platform because the registry
/// holds this dialect under another key.
fn check_registration(
    info: &crate::dialect::DialectInfo,
    registry: &crate::dialect::PlatformRegistry,
    findings: &mut Vec<Finding>,
) {
    let name = info.name;
    if matches!(
        crate::resolve::resolve_dialect_by_name_with_registry(name, registry),
        Err(crate::ResolveError::UnknownDialect { .. })
    ) {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: format!(
                "the name `{name}` does not resolve — nothing in this program registered it"
            ),
            fix: "add `inventory::submit! { DialectRegistration::new(\"<name>\", || \
                  Arc::new(MyDialect)) }` to your crate, and a `pub fn force_link() {}` beside \
                  it that the program using your dialect calls once. A crate nothing links is a \
                  crate the registry cannot see."
                .to_owned(),
        });
        return;
    }
    for spelling in info.spellings() {
        match crate::resolve::resolve_dialect_by_name_with_registry(spelling, registry) {
            Ok(found) if found.info().name == name => {}
            Ok(found) => findings.push(Finding {
                severity: Severity::Blocking,
                what: format!("`{spelling}` reaches `{}` rather than `{name}`", found.info().name),
                fix: format!(
                    "the registry holds `{name}` under another key. Register it under its own \
                     name, or drop `{spelling}` from its aliases."
                ),
            }),
            Err(crate::ResolveError::AmbiguousName { claimed_by, .. }) => findings.push(Finding {
                severity: Severity::Blocking,
                what: format!(
                    "`{spelling}` is claimed by more than one loaded platform ({}), so it names \
                     none of them — Razeri refuses that spelling rather than guessing which one \
                     a design meant",
                    claimed_by.join(" and ")
                ),
                fix: format!(
                    "give this dialect a name no other platform answers to. A platform name is \
                     read off the loaded dialects' own declared spellings, so a spelling another \
                     platform already claims is never `{name}`'s."
                ),
            }),
            Err(_) => findings.push(Finding {
                severity: Severity::Blocking,
                what: format!(
                    "`{spelling}` is declared as a spelling of `{name}` but reaches no platform"
                ),
                fix: format!(
                    "the `{name}` in the registry is a different build of this dialect and does \
                     not declare `{spelling}`. Register the one you are grading."
                ),
            }),
        }
    }
}

/// A family is a claim about spelling, so an unmeasured engine claiming a
/// measured family's name licenses SQL it may reject.
fn check_family(family: DialectFamily, findings: &mut Vec<Finding>) {
    if matches!(family, DialectFamily::Custom(name) if name.trim().is_empty()) {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "this dialect's family is a custom one with no name".to_owned(),
            fix: "give `DialectFamily::Custom` your engine's own name — it is what a report \
                  prints and what a reader looks up."
                .to_owned(),
        });
    }
}

/// The four required methods must answer for every type a design can declare.
fn check_required_rendering(dialect: &dyn PlatformDialect, findings: &mut Vec<Finding>) {
    let declarable = declarable_types();
    let empty_column: Vec<String> = declarable
        .iter()
        .filter(|dt| SqlRenderer::render_data_type(dialect, dt).trim().is_empty())
        .map(|dt| format!("{dt:?}"))
        .collect();
    if !empty_column.is_empty() {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: format!(
                "`render_data_type` answers nothing for {} of the types a design can declare",
                empty_column.len()
            ),
            fix: "every declarable type needs a column spelling on this engine, even if the \
                  spelling is a wider type that stores it. A blank answer becomes a column \
                  declaration with no type in it."
                .to_owned(),
        });
    }
    let empty_cast: Vec<String> = declarable
        .iter()
        .filter(|dt| SqlRenderer::render_cast_type(dialect, dt).trim().is_empty())
        .map(|dt| format!("{dt:?}"))
        .collect();
    if !empty_cast.is_empty() {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: format!(
                "`render_cast_type` answers nothing for {} declarable types",
                empty_cast.len()
            ),
            fix: "the generated load opens by casting every source column to its declared type, \
                  so a blank answer fails the load on its first statement."
                .to_owned(),
        });
    }
    let quoted = SqlRenderer::quote_identifier(dialect, "order");
    if quoted == "order" {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "`quote_identifier` returns the identifier unchanged, so a reserved word \
                   reaches this engine bare"
                .to_owned(),
            fix: "wrap the identifier in whatever this engine quotes with — double quotes, \
                  backticks, or brackets."
                .to_owned(),
        });
    }
    if SqlRenderer::render_current_timestamp(dialect).trim().is_empty() {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "`render_current_timestamp` answers nothing, and every generated load stamps \
                   a row with it"
                .to_owned(),
            fix: "return this engine's own expression for the current moment.".to_owned(),
        });
    }
}

/// **Reading a file in a named encoding**, where the dialect states a way to.
///
/// The same path question [`check_decisions`] asks of the plain relation, for
/// the same reason, plus one only this method can get wrong: an engine that
/// reads no file at all cannot read one in a named encoding, and a dialect that
/// answers here and not there states a relation nothing will ever ask it for.
///
/// Parameters:
/// - `dialect`: the plugin under test.
/// - `probe`: the same quoted path literal the plain relation was asked about.
/// - `findings`: where anything wrong is recorded.
fn check_encoded_file_relation(
    dialect: &dyn PlatformDialect,
    probe: &str,
    findings: &mut Vec<Finding>,
) {
    let Some(relation) =
        SqlRenderer::delimited_file_relation_in_encoding(dialect, probe, "windows-1252")
    else {
        return;
    };
    if !relation.contains(probe) {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "`delimited_file_relation_in_encoding` returns a relation that does not carry \
                   the path it was given"
                .to_owned(),
            fix: "put the literal you were handed where your engine's file relation takes a \
                  path. It arrives already quoted and escaped."
                .to_owned(),
        });
    }
    if SqlRenderer::delimited_file_relation(dialect, probe).is_none() {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "this dialect states how to read a file in a named encoding and states no way \
                   to read a file at all"
                .to_owned(),
            fix: "answer `delimited_file_relation` as well, or answer neither. Razeri asks the \
                  first question before the second — a source whose bytes are UTF-8 never \
                  reaches the encoding arm — so an engine that answers only the second has \
                  written a relation nothing will ask it for."
                .to_owned(),
        });
    }
}

/// The decisions a dialect states rather than inherits.
fn check_decisions(dialect: &dyn PlatformDialect, findings: &mut Vec<Finding>) {
    let spelling = SqlRenderer::sid_spelling(dialect);
    if spelling.platform == UNKNOWN_PLATFORM {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "this dialect states no surrogate-key spelling, so every key it renders calls \
                   an `xxhash64` its engine very likely does not have"
                .to_owned(),
            fix: "override `SqlRenderer::sid_spelling`. Say what this engine calls LOWER and \
                  TRIM, how it joins strings, how it casts to text, and how it spells a 64-bit \
                  hash. If it has no portable hash, name an artifact your prerequisites install \
                  — never the nearest-looking built-in, which keys a warehouse to a number \
                  nothing else can reproduce."
                .to_owned(),
        });
    }

    // **A stated body that says nothing is worse than no body at all.** Razeri
    // writes the `CREATE FUNCTION` envelope around whatever comes back, so an
    // empty one deploys cleanly and returns nothing — every key in the
    // warehouse is then the sentinel or garbage, under a green deploy.
    if let Some(supplied) = SqlRenderer::sid_helper_body(dialect)
        && supplied.body.trim().is_empty()
    {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "this dialect says its surrogate-key helper has a body Razeri cannot compose, \
                   and then supplies an empty one"
                .to_owned(),
            fix: "return the body that computes XXH64 with seed 0 over the UTF-8 bytes of the \
                  one argument, or answer `None` and let Razeri compose the derivation from \
                  your `sid_spelling`. An empty body deploys without error and keys every row \
                  to nothing."
                .to_owned(),
        });
    }

    // A file relation that drops its path reads the same file for every entity
    // — one table filled, the rest filled wrong, and nothing about it fails.
    let probe = "'/razeri/probe.csv'";
    if let Some(relation) = SqlRenderer::delimited_file_relation(dialect, probe)
        && !relation.contains(probe)
    {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "`delimited_file_relation` returns a relation that does not carry the path it \
                   was given"
                .to_owned(),
            fix: "put the literal you were handed where your engine's file relation takes a \
                  path. It arrives already quoted and escaped. A relation that drops it reads \
                  one file for every entity the design binds, and the generated fill loads the \
                  wrong rows without failing."
                .to_owned(),
        });
    }

    check_encoded_file_relation(dialect, probe, findings);
    check_routine_forms(dialect, findings);
    check_slice_replacement(dialect, findings);

    // The note is what a reader of the DDL learns from, and on an engine with
    // no keyword of its own it is the ONLY place they can learn it.
    if let ConstraintEnforcement::DeclaredOnly(declared) =
        DdlRenderer::constraint_enforcement(dialect)
        && declared.note.split_whitespace().count() < 5
    {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "this dialect says its engine accepts constraints it does not enforce, and \
                   the note explaining that says almost nothing"
                .to_owned(),
            fix: "a reader of your rendered DDL sees a PRIMARY KEY that looks like a \
                  guarantee. Say what this engine really does with the declaration, and where \
                  the guarantee has to come from instead."
                .to_owned(),
        });
    }

    // **The two refusals are different findings, and that is the point of the
    // second variant.** `None` is silence, and silence is unanswered. A stated
    // `Unsupported` is a measured claim; what is left to grade there is whether
    // the sentence is worth reading, because it is the only thing an operator
    // gets where the load would have been.
    match DialectCapabilities::merge_shape(dialect) {
        MergeShape::None => findings.push(Finding {
            severity: Severity::Unanswered,
            what: "this dialect has not stated its upsert shape, so Razeri writes no generated \
                   load for it"
                .to_owned(),
            fix: "if this engine has a MERGE or an upsert statement, say which in \
                  `DialectCapabilities::merge_shape`. If it genuinely has neither, answer \
                  `MergeShape::Unsupported` with your engine's own sentence — a refusal an \
                  operator can act on, rather than a silence."
                .to_owned(),
        }),
        MergeShape::Unsupported(orientation) => {
            check_refusal_copy("the upsert refusal", orientation, findings);
        }
        MergeShape::Merge(restrictions) => check_merge_restrictions(restrictions, findings),
        _ => {}
    }
}

/// **A dialect that names a verb for replacing one slice has to put the slice
/// in it.**
///
/// Most dialects answer nothing here, and nothing is a complete answer: Razeri
/// then writes a delete filtered to the slice, which is correct on every
/// engine. What is worth grading is the dialect that *does* answer, because its
/// statement runs in front of a load's write and clears rows. A statement that
/// forgot the value it was handed does not clear the day this call was given —
/// it clears some other day, or every day, and the load then reports success
/// over a table it emptied.
///
/// The probe is a daily partition of a date column, which is the case every
/// partition-level verb is allowed to answer for. A dialect that answers
/// nothing to it has said the portable form is what it wants.
fn check_slice_replacement(dialect: &dyn PlatformDialect, findings: &mut Vec<Finding>) {
    const VALUE: &str = "$razeri_slice_probe";
    let plan = StoragePlan {
        partition: PartitionStrategy::RangeByTimeDimension {
            field: "razeri_probe_day".to_owned(),
            granularity: PartitionGranularity::Day,
            retention: None,
            look_ahead: None,
            window: razeri_plugin_contract::storage_strategy::PartitionWindow::default(),
        },
        compression: CompressionStrategy::None,
        index: IndexStrategy::None,
    };
    let day = DataType::date();
    let columns = ["razeri_probe_day"];
    let entity = EntityRef {
        schema: Some("razeri_probe"),
        name: "razeri_probe_table",
        is_identity_table: false,
        columns: &columns,
        partition_column_type: Some(&day),
    };
    let slice = SliceRef { column: "razeri_probe_day", value: VALUE };
    let Some(answer) = StorageRenderer::render_slice_replacement(dialect, entity, &plan, slice)
    else {
        return;
    };

    let carries = match &answer {
        SliceReplacement::Emptied(statements) => {
            !statements.is_empty() && statements.iter().all(|sql| sql.contains(VALUE))
        }
        SliceReplacement::WrittenByInsert(clause) => clause.contains(VALUE),
    };
    // **A verb that carries the slice is graded nowhere**, deliberately. The
    // kit cannot tell a measured answer from a lucky one, and a note on every
    // dialect that got it right would fire on exactly the dialects that need no
    // help. What is left to say is said where it is useful — in the trait's own
    // documentation, which an author reads before writing the override.
    if carries {
        return;
    }
    findings.push(Finding {
        severity: Severity::Blocking,
        what: "`render_slice_replacement` returns a statement that does not carry the slice it \
               was handed"
            .to_owned(),
        fix: "put the value you were given where your statement names the slice, and build any \
              partition NAME from it the same way your extend procedure built it. A replacement \
              that drops the value clears a slice this call was not given — or every slice — \
              and the load reports success over what it emptied."
            .to_owned(),
    });
}

/// **The two halves of an evolution, held together**: what this engine says it
/// keeps when a loaded table changes shape, and the statement it writes for the
/// change.
///
/// An answer left at its default is graded nowhere, for the reason
/// [`check_merge_restrictions`] states: from outside, a measured *"my engine
/// does not do that"* and a question nobody asked read the same, and a finding
/// made out of that silence would fire on every dialect.
///
/// What is worth saying is a **pair that disagrees**. A dialect that says its
/// engine widens a string in place and then writes no statement for a widening
/// has told Razeri to call the change safe and left the operator to work out
/// the `ALTER` alone — a gap that reads to them as Razeri not having finished.
/// And a dialect that answers `None` to a new column has declined the one
/// evolution every warehouse has, which is nearly always an override that meant
/// to narrow something and narrowed everything.
fn check_evolution(dialect: &dyn PlatformDialect, findings: &mut Vec<Finding>) {
    let answers = DialectCapabilities::evolution_answers(dialect);
    let boolean = DataType::boolean();
    let long = DataType::varchar(40);

    if DdlRenderer::render_column_evolution(
        dialect,
        &ColumnEvolution::AddColumn {
            schema: Some("s"),
            table: "t",
            column: "c",
            data_type: &boolean,
        },
    )
    .is_none()
    {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "this dialect writes no statement for a column that is new, which is the                    commonest change a deployed warehouse ever sees"
                .to_owned(),
            fix: "answer `ColumnEvolution::AddColumn` in `render_column_evolution`, or drop the                   override and take the contract's `ALTER TABLE … ADD COLUMN …`, which is this                   spelling on every engine Razeri reaches. An engine that genuinely has no way                   to add a column is worth saying out loud in the crate's own documentation."
                .to_owned(),
        });
    }

    if answers.parameterized_string_widening_is_lossless
        && DdlRenderer::render_column_evolution(
            dialect,
            &ColumnEvolution::WidenColumn {
                schema: Some("s"),
                table: "t",
                column: "c",
                data_type: &long,
            },
        )
        .is_none()
    {
        findings.push(Finding {
            severity: Severity::Note,
            what: "this dialect says its engine widens a string's declared length in place, and                    writes no statement for the change"
                .to_owned(),
            fix: "answer `ColumnEvolution::WidenColumn` in `render_column_evolution` with this                   engine's spelling of it. Without it Razeri tells an operator the widening                   costs nothing and then hands them nothing to run, which reads as Razeri not                   having finished rather than as a statement they own."
                .to_owned(),
        });
    }

    if answers.nested_field_addition_is_lossless
        && DdlRenderer::render_column_evolution(
            dialect,
            &ColumnEvolution::AddNestedField {
                schema: Some("s"),
                table: "t",
                column: "c",
                field: "f",
                data_type: &long,
            },
        )
        .is_none()
    {
        findings.push(Finding {
            severity: Severity::Note,
            what: "this dialect says its engine keeps every value when a record gains a field,                    and writes no statement for the change"
                .to_owned(),
            fix: "answer `ColumnEvolution::AddNestedField` in `render_column_evolution`. Some                   engines name the new field; some restate the whole column's type, which is                   why the change carries both the field's path and the column's type with the                   field in it."
                .to_owned(),
        });
    }
}

/// **What a stated `MERGE` restriction changes about the SQL Razeri writes for
/// this engine**, said back to the author while the claim is still cheap to
/// withdraw.
///
/// A restriction left at its default costs nothing and is graded nowhere: the
/// kit cannot tell a measured *"my engine is fine with this"* from a question
/// nobody asked, and inventing a finding out of that silence would fire on
/// every dialect. What it can do is report the restriction a dialect does
/// state, because each one makes Razeri emit something other than the
/// statement it emits everywhere else.
fn check_merge_restrictions(restrictions: MergeRestrictions, findings: &mut Vec<Finding>) {
    if restrictions.slice_pruning_needs_literal {
        findings.push(Finding {
            severity: Severity::Note,
            what: "this dialect says its planner reads one slice of a partitioned table only \
                   from a literal, so a load scoped to one day cannot simply bind the day"
                .to_owned(),
            fix: "Razeri will put the day into the statement text through this engine's \
                  dynamic-execution form rather than binding it to the load procedure's \
                  parameter. Confirm that is what your engine wants: the statement is composed \
                  once per call and its text differs per day, which some planners cache and \
                  some do not. If a bound parameter does prune here, drop the restriction and \
                  Razeri binds it like everywhere else."
                .to_owned(),
        });
    }
}

/// The one override nothing tells an author about, and every formula in every
/// design goes through it.
fn check_formula_renderer(dialect: &dyn PlatformDialect, findings: &mut Vec<Finding>) {
    let formula = SqlRenderer::to_formula_renderer(dialect);
    let dialect_name = SqlRenderer::dialect_name(dialect);
    if formula.dialect_name() != dialect_name && dialect_name != "ansi" {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: "`to_formula_renderer` was not overridden, so every formula in every design \
                   renders through Razeri's ANSI defaults instead of this dialect"
                .to_owned(),
            fix: "return `Box::new(Self)`. It is one line, nothing fails without it, and every \
                  formula this engine sees is silently somebody else's."
                .to_owned(),
        });
    }
}

/// **The three routine grammars a dialect states**, and what each answer owes.
///
/// A grammar Razeri carries needs nothing further. A refusal owes words a
/// reader can act on. `Custom` owes the render method it promised — see
/// [`check_custom_grammar`].
fn check_routine_forms(dialect: &dyn PlatformDialect, findings: &mut Vec<Finding>) {
    match SqlRenderer::procedure_form(dialect) {
        // Razeri's own agnostic renderer answers `Agnostic` on purpose: the
        // annotated form IS its output. Every other dialect that answers it has
        // simply not said.
        ProcedureForm::Agnostic if SqlRenderer::is_agnostic_dialect(dialect) => {}
        ProcedureForm::Agnostic => findings.push(Finding {
            severity: Severity::Unanswered,
            what: "this dialect states no stored-procedure grammar, so Razeri emits its own \
                   annotated form — which no engine parses"
                .to_owned(),
            fix: "override `SqlRenderer::procedure_form` with the grammar this engine speaks, \
                  or with `ProcedureForm::Unsupported(\"…\")` and a sentence saying what it \
                  offers instead."
                .to_owned(),
        }),
        ProcedureForm::Unsupported(orientation) => {
            check_refusal_copy("the stored-procedure refusal", orientation, findings);
        }
        ProcedureForm::Custom(grammar) => check_custom_grammar(
            CustomGrammar {
                kind: RoutineKind::Procedure,
                grammar,
                form_method: "procedure_form",
                render_method: "render_procedure",
                noun: "procedures",
            },
            |spec| SqlRenderer::render_procedure(dialect, spec),
            findings,
        ),
        _ => {}
    }

    match SqlRenderer::scalar_function_form(dialect) {
        ScalarFunctionForm::Unsupported(orientation) => {
            check_refusal_copy("the scalar-function refusal", orientation, findings);
        }
        ScalarFunctionForm::Custom(grammar) => check_custom_grammar(
            CustomGrammar {
                kind: RoutineKind::ScalarFunction,
                grammar,
                form_method: "scalar_function_form",
                render_method: "render_scalar_function",
                noun: "scalar functions",
            },
            |spec| SqlRenderer::render_scalar_function(dialect, spec),
            findings,
        ),
        _ => {}
    }

    match SqlRenderer::table_function_form(dialect) {
        TableFunctionForm::Unsupported(orientation) => {
            check_refusal_copy("the table-function refusal", orientation, findings);
        }
        TableFunctionForm::Custom(grammar) => check_custom_grammar(
            CustomGrammar {
                kind: RoutineKind::TableFunction,
                grammar,
                form_method: "table_function_form",
                render_method: "render_table_function",
                noun: "table functions",
            },
            |spec| SqlRenderer::render_table_function(dialect, spec),
            findings,
        ),
        _ => {}
    }

    check_parameter_type_spelling(dialect, findings);
}

/// **A parameter's type is not always spelled the way a column's is**, and this
/// asks whether the dialect has looked.
///
/// Oracle is the measured case: a column there takes `NUMBER(19, 0)` and
/// `VARCHAR2(100)`, and the same types in a parameter list are a compile error
/// — the bare `NUMBER` and `VARCHAR2` are what a parameter clause takes, with
/// the precision belonging on the local declaration instead. A dialect that has
/// not said otherwise gets the column spelling in its parameter lists, which is
/// right for most engines and a routine that will not compile on one like that.
///
/// It is a note and not a failure, because for most engines the two spellings
/// genuinely are the same and there is nothing to say. And it is asked only of a
/// dialect spelling a grammar of its own, because that is the population where
/// nobody has measured the answer yet.
fn check_parameter_type_spelling(dialect: &dyn PlatformDialect, findings: &mut Vec<Finding>) {
    let spells_its_own = SqlRenderer::procedure_form(dialect).custom_grammar().is_some()
        || SqlRenderer::scalar_function_form(dialect).custom_grammar().is_some()
        || SqlRenderer::table_function_form(dialect).custom_grammar().is_some();
    if !spells_its_own {
        return;
    }
    // A type that carries a length is the only kind the two spellings can
    // disagree about, so it is the only kind worth asking with.
    let qualified = DataType::varchar(100);
    let column = SqlRenderer::render_data_type(dialect, &qualified);
    let parameter = SqlRenderer::render_parameter_data_type(dialect, &qualified);
    if column == parameter && column.contains('(') {
        findings.push(Finding {
            severity: Severity::Note,
            what: format!(
                "a parameter of this routine's would be declared `{parameter}`, the same as a                  column of that type"
            ),
            fix: "that is right for most engines, so this is only worth a look. If yours refuses                   a length or a precision in a parameter list — Oracle does, and answers                   PLS-00103 at the opening parenthesis — override                   `SqlRenderer::render_parameter_data_type` with the bare spelling. Local                   declarations keep the length either way."
                .to_owned(),
        });
    }
}

/// One routine kind whose grammar a dialect said it spells itself.
#[derive(Clone, Copy)]
struct CustomGrammar {
    /// Which routine kind the claim is about.
    kind: RoutineKind,
    /// The grammar's own name, as the dialect wrote it.
    grammar: &'static str,
    /// The method that carried the claim.
    form_method: &'static str,
    /// The method that owes the rendering.
    render_method: &'static str,
    /// What to call the routines in a sentence.
    noun: &'static str,
}

/// **A dialect that says it spells its own grammar has to spell it.**
///
/// `Custom` moves the whole rendering to the dialect: Razeri substitutes no
/// near-neighbour grammar and refuses nothing, because both of those say
/// something false — one about the engine's syntax, the other about whether the
/// engine has the routine at all. So the claim is only worth anything with the
/// method behind it, and a dialect that made the claim and left the method
/// alone ships a build that stops on the routine.
///
/// The check is the question itself: hand the render method the shape it will
/// receive and see whether anything comes back.
///
/// Parameters:
/// - `claim`: which kind, which grammar, and the two method names to name;
/// - `render`: the dialect's render method for that kind;
/// - `findings`: where the report is collected.
fn check_custom_grammar(
    claim: CustomGrammar,
    render: impl Fn(&RoutineSpec) -> Option<String>,
    findings: &mut Vec<Finding>,
) {
    let CustomGrammar { kind, grammar, form_method, render_method, noun } = claim;
    // The grammar's name is a name, not a refusal: it is read in a report and
    // in a comment, so it has to say something and does not have to say much.
    if grammar.trim().is_empty() {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: format!("`{form_method}` says Custom, and names no grammar"),
            fix: "carry your grammar's own name — `Custom(\"PL/SQL\")`. It is what a reader \
                  of a report, and of the comment Razeri writes where a routine could not be \
                  rendered, is told this engine speaks."
                .to_owned(),
        });
    }

    let mut probe = RoutineSpec::new(kind, "razeri_conformance_probe");
    probe.or_replace = true;
    if render(&probe).is_none_or(|rendered| rendered.trim().is_empty()) {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: format!(
                "`{form_method}` says Custom({grammar:?}), so this dialect must render {noun} \
                 itself — and `{render_method}` returns nothing"
            ),
            fix: format!(
                "override `SqlRenderer::{render_method}`. It receives the routine Razeri \
                 composed — name, parameters with their types already in your spelling, body, \
                 comment — and returns the whole CREATE statement your engine parses. Razeri \
                 emits what you return and writes nothing of its own: a near-neighbour grammar \
                 fails on deploy, and a refusal would say this engine has no {noun} when it \
                 has them in a grammar of its own."
            ),
        });
    }
}

/// A refusal that does not say what to do instead is a wall.
fn check_refusal_copy(subject: &str, copy: &str, findings: &mut Vec<Finding>) {
    if copy.trim().is_empty() {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: format!("{subject} has no words in it"),
            fix: "say what this engine offers instead. A reader who hits a refusal needs the \
                  next thing to try, and it has to be about their engine."
                .to_owned(),
        });
        return;
    }
    if copy.split_whitespace().count() < 5 {
        findings.push(Finding {
            severity: Severity::Note,
            what: format!("{subject} is very short"),
            fix: "a refusal earns its place by naming the alternative — what this engine has \
                  instead of the thing it cannot do."
                .to_owned(),
        });
    }
}

/// Fourteen facts are declared twice and must agree.
fn check_paired_facts(dialect: &dyn PlatformDialect, findings: &mut Vec<Finding>) {
    let caps: &dyn DialectCapabilities = dialect;
    let ren: &dyn SqlRenderer = dialect;
    let ddl: &dyn DdlRenderer = dialect;
    let mut disagreements: Vec<&'static str> = Vec::new();

    macro_rules! pair {
        ($m:ident, $renderer_value:expr) => {
            if caps.$m() != $renderer_value {
                disagreements.push(stringify!($m));
            }
        };
    }
    pair!(supports_on_conflict, ren.supports_on_conflict());
    pair!(supports_insert_overwrite, ren.supports_insert_overwrite());
    pair!(supports_update_from, ren.supports_update_from());
    pair!(supports_named_windows, ren.supports_named_windows());
    pair!(supports_compound_assignment, ren.supports_compound_assignment());
    pair!(supports_window_frame_exclude, ren.supports_window_frame_exclude());
    pair!(supports_merge_not_matched_by_source, ren.supports_merge_not_matched_by_source());
    pair!(merge_not_matched_keyword, ren.merge_not_matched_keyword());
    pair!(uses_alter_table_update, ren.uses_alter_table_update());
    pair!(supports_multi_table_insert, ren.supports_multi_table_insert());
    pair!(supports_cascade_drop, ddl.supports_cascade_drop());
    pair!(supports_sync_drop, ddl.supports_sync_drop());
    pair!(supports_force_drop, ddl.supports_force_drop());

    // **The fourteenth, whose two sides are different types.** The capability
    // is a boolean; the renderer answer is a form that either renders or
    // carries a refusal. Both are read — the build door reads the form, and
    // registry-walking rosters read the capability — so a dialect claiming a
    // table function on one side and refusing on the other has an engine that
    // both does and does not have one. `SQLite` was exactly that on the day
    // this check was written: `false` since the capability existed, and a
    // renderer still inheriting PostgreSQL's `RETURNS TABLE`.
    if caps.supports_table_functions() != ren.table_function_form().refusal().is_none() {
        disagreements.push("supports_table_functions");
    }

    if !disagreements.is_empty() {
        findings.push(Finding {
            severity: Severity::Blocking,
            what: format!(
                "this dialect declares {} fact(s) two ways and the two disagree: {}",
                disagreements.len(),
                disagreements.join(", ")
            ),
            fix: "each of these is declared once on the capability trait and once in the \
                  renderer hierarchy, and Razeri reads both. Decide which is true of your engine \
                  and move the other one to match."
                .to_owned(),
        });
    }
}

/// Every type a design can declare, which is the set the required methods owe
/// an answer for.
///
/// The last four are the ones whose spelling actually varies between engines:
/// an array, a map, a struct, and an array of structs. A dialect that answers
/// only for scalars is a dialect that has not been graded on the types a
/// nested source table is made of.
fn declarable_types() -> Vec<DataType> {
    vec![
        DataType::tinyint(),
        DataType::smallint(),
        DataType::int(),
        DataType::bigint(),
        DataType::double(),
        DataType::boolean(),
        DataType::text(),
        DataType::varchar(200),
        DataType::uuid(),
        DataType::json(),
        DataType::date(),
        DataType::timestamp(),
        DataType::timestamp_tz(),
        DataType::decimal(18, 2),
        DataType::Array(ArrayDataType::new(DataType::varchar(100))),
        DataType::Map(MapDataType::new(DataType::varchar(50), DataType::bigint())),
        DataType::Struct(StructDataType::new(vec![
            StructField::new("street", DataType::varchar(200)),
            StructField::new("zip", DataType::varchar(10)),
        ])),
        DataType::Array(ArrayDataType::new(DataType::Struct(StructDataType::new(vec![
            StructField::new("key", DataType::varchar(100)),
            StructField::new("value", DataType::varchar(1000)),
        ])))),
    ]
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::dialect::DialectInfo;
    use razeri_plugin_contract::{
        Concat, DmlRenderer, ExpressionRenderer, FormulaRenderer, MergeRestrictions,
        ProcedureRenderer, ReplicationRenderer, ScalarFunctionForm, SidSpelling, StorageRenderer,
        TaskRenderer, TextCast,
    };
    use std::marker::PhantomData;

    // ── The broken fixture ────────────────────────────────────────────
    //
    // A plugin that compiles, registers nothing it should, and answers every
    // question with somebody else's default. This is what the kit exists to
    // catch, and it is deliberately the plugin an author gets by implementing
    // only the four required methods and stopping — which the guide, until
    // now, told them was enough.

    struct BrokenPlugin;

    impl SqlRenderer for BrokenPlugin {
        fn render_data_type(&self, _dt: &DataType) -> String {
            String::new()
        }
        fn quote_identifier(&self, name: &str) -> String {
            name.to_owned()
        }
        fn render_cast_type(&self, _dt: &DataType) -> String {
            String::new()
        }
        fn qualify_name(&self, _schema: Option<&str>, name: &str) -> String {
            name.to_owned()
        }
        fn render_current_timestamp(&self) -> String {
            String::new()
        }
        fn dialect_name(&self) -> &'static str {
            "brokendb"
        }
        // No `sid_spelling`, no `procedure_form`, no `to_formula_renderer` —
        // and one fact declared twice, two ways.
        fn supports_on_conflict(&self) -> bool {
            true
        }
    }
    impl ExpressionRenderer for BrokenPlugin {}
    impl DdlRenderer for BrokenPlugin {}
    impl DmlRenderer for BrokenPlugin {}
    impl ProcedureRenderer for BrokenPlugin {}
    impl FormulaRenderer for BrokenPlugin {}
    impl TaskRenderer for BrokenPlugin {}
    impl ReplicationRenderer for BrokenPlugin {}
    impl StorageRenderer for BrokenPlugin {}
    impl DialectCapabilities for BrokenPlugin {
        fn supports_on_conflict(&self) -> bool {
            false
        }
    }
    impl PlatformDialect for BrokenPlugin {
        fn info(&self) -> DialectInfo {
            DialectInfo {
                name: "brokendb",
                display_name: "Broken DB",
                aliases: &[],
                dialect_family: DialectFamily::Custom(""),
                family: "Broken",
                is_cloud_native: false,
                is_olap: false,
                is_postgres_compatible: false,
            }
        }
    }

    // ── The answered fixture, under two names ─────────────────────────
    //
    // The same plugin with every question answered, carrying the name it
    // registers under as a type parameter. Neither name is one Razeri knows a
    // spelling for; the difference is that one of them is in the registry and
    // the other is in nothing at all. Those are two different facts about a
    // dialect, and they read as two different reports.

    trait FixtureName: Send + Sync + 'static {
        /// The registry name this fixture answers to.
        const NAME: &'static str;
        /// How this fixture's engine joins the parts of a composite key. Most
        /// of them take the inherited variadic `CONCAT`; the one that does not
        /// is the point of it being a knob.
        const CONCAT: Concat = Concat::Function("CONCAT");
    }

    /// Answered, and nothing linked it — what an author sees running the report
    /// from a crate whose registration nobody calls.
    struct Unlinked;
    impl FixtureName for Unlinked {
        const NAME: &'static str = "healthydb";
    }

    /// Answered and registered, under a name Razeri ships no spelling for —
    /// the shape of every dialect written outside Razeri's own tree.
    struct Outside;
    impl FixtureName for Outside {
        const NAME: &'static str = "outsidedb";
    }

    /// Answered, and joining composite keys with a `CONCAT` that takes exactly
    /// two arguments — the shape of Db2 and of older Oracle releases. Nothing
    /// about the join is an obligation, so the report on it must read exactly
    /// like the report on a variadic engine.
    struct BinaryConcat;
    impl FixtureName for BinaryConcat {
        const NAME: &'static str = "binaryconcatdb";
        const CONCAT: Concat = Concat::FunctionBinary("CONCAT");
    }

    struct Answered<N: FixtureName>(PhantomData<N>);

    impl<N: FixtureName> Answered<N> {
        const fn new() -> Self {
            Self(PhantomData)
        }
    }

    type HealthyPlugin = Answered<Unlinked>;
    type OutsidePlugin = Answered<Outside>;

    inventory::submit! {
        crate::builder::DialectRegistration::new(
            Outside::NAME,
            || std::sync::Arc::new(OutsidePlugin::new()),
        )
    }

    impl<N: FixtureName> SqlRenderer for Answered<N> {
        fn render_data_type(&self, dt: &DataType) -> String {
            razeri_plugin_contract::agnostic::render_data_type_ansi(dt)
        }
        fn quote_identifier(&self, name: &str) -> String {
            format!("\"{name}\"")
        }
        fn qualify_name(&self, schema: Option<&str>, name: &str) -> String {
            schema.map_or_else(
                || self.quote_identifier(name),
                |s| format!("{}.{}", self.quote_identifier(s), self.quote_identifier(name)),
            )
        }
        fn render_current_timestamp(&self) -> String {
            "NOW()".to_owned()
        }
        fn dialect_name(&self) -> &'static str {
            N::NAME
        }
        fn sid_spelling(&self) -> SidSpelling {
            SidSpelling {
                platform: N::NAME,
                hash: ("answered_xxhash64(", ")"),
                cast_type: TextCast::Direct("STRING"),
                concat: N::CONCAT,
                through_helper: false,
                ..razeri_plugin_contract::ANSI_SID_SPELLING
            }
        }
        fn procedure_form(&self) -> ProcedureForm {
            ProcedureForm::Unsupported(
                "This engine has no stored procedures; write the load as a scheduled query \
                 instead.",
            )
        }
        fn scalar_function_form(&self) -> ScalarFunctionForm {
            ScalarFunctionForm::PostgreSql
        }
        fn to_formula_renderer(&self) -> Box<dyn FormulaRenderer> {
            Box::new(Self::new())
        }
    }
    impl<N: FixtureName> ExpressionRenderer for Answered<N> {}
    impl<N: FixtureName> DdlRenderer for Answered<N> {}
    impl<N: FixtureName> DmlRenderer for Answered<N> {}
    impl<N: FixtureName> ProcedureRenderer for Answered<N> {}
    impl<N: FixtureName> FormulaRenderer for Answered<N> {}
    impl<N: FixtureName> TaskRenderer for Answered<N> {}
    impl<N: FixtureName> ReplicationRenderer for Answered<N> {}
    impl<N: FixtureName> StorageRenderer for Answered<N> {}
    impl<N: FixtureName> DialectCapabilities for Answered<N> {
        fn merge_shape(&self) -> MergeShape {
            MergeShape::Merge(MergeRestrictions::none())
        }
    }
    impl<N: FixtureName> PlatformDialect for Answered<N> {
        fn info(&self) -> DialectInfo {
            DialectInfo {
                name: N::NAME,
                display_name: "An Answered Engine",
                // It answers to its own name and nothing else, which is the
                // shape of a plugin that declares no extra spellings.
                aliases: &[],
                dialect_family: DialectFamily::Custom(N::NAME),
                family: "Answered",
                is_cloud_native: false,
                is_olap: false,
                is_postgres_compatible: false,
            }
        }
    }

    // ── The twin: a dialect that claims a name another platform answers to ──
    //
    // Answered in every other respect, so the only thing its report can be
    // about is the spelling it took.

    struct Twin;

    impl SqlRenderer for Twin {
        fn render_data_type(&self, dt: &DataType) -> String {
            razeri_plugin_contract::agnostic::render_data_type_ansi(dt)
        }
        fn quote_identifier(&self, name: &str) -> String {
            format!("\"{name}\"")
        }
        fn qualify_name(&self, _schema: Option<&str>, name: &str) -> String {
            self.quote_identifier(name)
        }
        fn render_current_timestamp(&self) -> String {
            "NOW()".to_owned()
        }
    }
    impl ExpressionRenderer for Twin {}
    impl DdlRenderer for Twin {}
    impl DmlRenderer for Twin {}
    impl ProcedureRenderer for Twin {}
    impl FormulaRenderer for Twin {}
    impl TaskRenderer for Twin {}
    impl ReplicationRenderer for Twin {}
    impl StorageRenderer for Twin {}
    impl DialectCapabilities for Twin {}
    impl PlatformDialect for Twin {
        fn info(&self) -> DialectInfo {
            DialectInfo {
                name: "twindb",
                display_name: "Twin DB",
                // The name the answered fixture already answers to.
                aliases: &["healthydb"],
                dialect_family: DialectFamily::Custom("twindb"),
                family: "Twin",
                is_cloud_native: false,
                is_olap: false,
                is_postgres_compatible: false,
            }
        }
    }

    /// Every finding whose `what` line mentions one of these subjects.
    fn mentions(report: &Report, needle: &str) -> bool {
        report.findings.iter().any(|f| f.what.contains(needle) || f.fix.contains(needle))
    }

    /// **The kit's own red.** A plugin that implements the four required
    /// methods and stops is exactly what the guide used to produce, and every
    /// one of these findings is a defect a shipped dialect actually had.
    #[test]
    fn the_kit_catches_a_deliberately_broken_plugin() {
        let report = check(&BrokenPlugin);
        assert!(!report.is_clean(), "the broken plugin reported clean:\n{report}");

        assert!(mentions(&report, "does not resolve"), "unregistered:\n{report}");
        assert!(mentions(&report, "custom one with no name"), "unnamed family:\n{report}");
        assert!(mentions(&report, "render_data_type"), "empty column types:\n{report}");
        assert!(mentions(&report, "render_cast_type"), "empty cast types:\n{report}");
        assert!(mentions(&report, "identifier unchanged"), "no quoting:\n{report}");
        assert!(mentions(&report, "render_current_timestamp"), "no now():\n{report}");
        assert!(mentions(&report, "surrogate-key spelling"), "unspelled key:\n{report}");
        assert!(mentions(&report, "stored-procedure grammar"), "no procedure form:\n{report}");
        assert!(mentions(&report, "upsert shape"), "no merge shape:\n{report}");
        assert!(mentions(&report, "to_formula_renderer"), "formula renderer:\n{report}");
        assert!(mentions(&report, "supports_on_conflict"), "paired fact:\n{report}");

        assert!(
            report.count(Severity::Blocking) >= 8,
            "the broken plugin owes more than {} blocking fixes:\n{report}",
            report.count(Severity::Blocking)
        );
    }

    /// **The kit does not cry wolf.** The same plugin with its questions
    /// answered reports only what is actually true of it: it is not
    /// registered in this test binary, and nothing else.
    #[test]
    fn the_kit_reports_only_registration_on_a_plugin_that_answered_everything() {
        let report = check(&HealthyPlugin::new());
        let unregistered: Vec<&Finding> =
            report.findings.iter().filter(|f| f.what.contains("does not resolve")).collect();
        assert_eq!(unregistered.len(), 1, "the registration finding is the honest one here");
        assert_eq!(
            report.findings.len(),
            1,
            "a plugin that answered every question owes nothing else:\n{report}"
        );
    }

    /// **A join written for a two-argument `CONCAT` is an answer, not a
    /// shortfall.** The report on a dialect that states it reads exactly like
    /// the report on a variadic one, and the key it renders nests pairwise
    /// instead of widening a call the engine does not have.
    #[test]
    fn the_kit_takes_a_two_argument_concat_as_an_answer_like_any_other() {
        let binary = Answered::<BinaryConcat>::new();
        let report = check(&binary);
        assert_eq!(
            report.findings.len(),
            check(&HealthyPlugin::new()).findings.len(),
            "the join form is a decision, so stating this one owes nothing extra:\n{report}"
        );
        assert!(
            !report.to_string().contains("joins"),
            "nothing about the join is outstanding:\n{report}"
        );

        let key = razeri_plugin_contract::sid::sid_expression(
            SqlRenderer::sid_spelling(&binary),
            None,
            &["a".to_owned(), "b".to_owned(), "c".to_owned()],
        );
        assert!(
            key.contains("CONCAT(CONCAT("),
            "a two-argument engine gets one call per pair:\n{key}"
        );
    }

    /// **A stated `MERGE` restriction is reported; a default one is not.**
    ///
    /// The asymmetry is the point. A dialect that says its planner needs a
    /// literal slice gets Razeri's plan for that answer back, while the engine
    /// it is describing is still in front of the author. A dialect that has
    /// said nothing gets nothing, because the kit cannot tell a measured
    /// *"a parameter is fine here"* from a question never asked, and a finding
    /// made out of that silence would fire on every dialect alike.
    #[test]
    fn a_stated_merge_restriction_is_reported_and_a_default_one_is_not() {
        let mut quiet = Vec::new();
        check_merge_restrictions(MergeRestrictions::none(), &mut quiet);
        assert!(quiet.is_empty(), "a dialect with no stated restriction is asked nothing");

        let mut stated = Vec::new();
        check_merge_restrictions(MergeRestrictions::requiring_a_literal_slice(), &mut stated);
        assert_eq!(stated.len(), 1, "the stated restriction is reported once");
        assert_eq!(stated[0].severity, Severity::Note, "nothing is broken; it is worth a look");
        assert!(
            stated[0].what.contains("literal"),
            "the finding names the restriction:\n{}",
            stated[0].what
        );
        assert!(
            stated[0].fix.contains("dynamic-execution"),
            "and says what Razeri does with the answer:\n{}",
            stated[0].fix
        );

        // The other restriction travels on the same struct and must not drag
        // the new finding along with it.
        let mut two_clauses = Vec::new();
        check_merge_restrictions(MergeRestrictions::requiring_two_when_clauses(), &mut two_clauses);
        assert!(two_clauses.is_empty(), "one restriction is not the other");
    }

    /// **A dialect written outside Razeri reaches a clean report.** It is
    /// reached the way every out-of-tree dialect is reached — it registered, and
    /// the resolver reads the loaded dialects' own declared spellings — so there
    /// is nothing for Razeri to be missing it from and nothing for the report to
    /// ask of its author.
    #[test]
    fn a_dialect_registered_under_its_own_name_reaches_a_clean_report() {
        assert!(
            crate::resolve_dialect_by_name(Outside::NAME).is_ok(),
            "the fixture registers through the registry, which is the whole path being graded"
        );
        // The precondition that used to read "no row in Razeri's table": no
        // other loaded platform declares this name, so the fixture is reached
        // only because it registered and said so itself.
        let registry = crate::dialect::PlatformRegistry::with_auto_discovered();
        assert!(
            registry
                .list()
                .iter()
                .filter(|info| info.name != Outside::NAME)
                .all(|info| !info.answers_to(Outside::NAME)),
            "the fixture's name must be one no other platform claims"
        );

        let report = check(&OutsidePlugin::new());
        assert!(report.findings.is_empty(), "nothing is owed here:\n{report}");
        assert!(report.is_clean(), "and the report says so:\n{report}");
        assert_eq!(report.count(Severity::Blocking), 0, "{report}");
        assert!(
            report.to_string().contains("nothing to fix"),
            "a clean dialect is told it is clean:\n{report}"
        );
    }

    /// **A platform cannot be reachable under an alias but not under its own
    /// name.** That used to be a judgement about a hand-written table, which
    /// could spell a platform `mynew_db` and never `mynewdb`. A dialect now
    /// declares its own spellings and its own name leads them, so the defect is
    /// unrepresentable rather than caught — and this is the assertion that keeps
    /// it that way.
    #[test]
    fn a_platform_is_never_reachable_by_an_alias_but_not_by_its_own_name() {
        let registry = crate::dialect::PlatformRegistry::with_auto_discovered();
        for info in registry.list() {
            assert_eq!(
                info.spellings().first().copied(),
                Some(info.name),
                "a platform's own name leads its spellings"
            );
            assert!(info.answers_to(info.name), "{} answers to its own name", info.name);
        }
    }

    /// **A name another platform already answers to is a collision, not a
    /// registration.** A dialect claiming a spelling Healthy DB answers to is
    /// named as the collision it is — with both platforms named, and a fix its
    /// author can actually perform — rather than being reported as an
    /// unregistered platform, which is a different problem with a different fix.
    #[test]
    fn a_name_razeri_reads_as_another_platform_is_blocking_and_says_which() {
        let mut registry = crate::dialect::PlatformRegistry::new();
        registry.register("healthydb".to_owned(), std::sync::Arc::new(HealthyPlugin::new()));
        registry.register("twindb".to_owned(), std::sync::Arc::new(Twin));

        let report = check_with_registry(&Twin, &registry);
        let collision = report
            .findings
            .iter()
            .find(|f| f.what.contains("claimed by more than one loaded platform"))
            .unwrap_or_else(|| panic!("the collision is reported:\n{report}"));
        assert_eq!(collision.severity, Severity::Blocking, "{collision:?}");
        assert!(collision.what.contains("healthydb"), "the other platform is named: {collision:?}");
        assert!(collision.what.contains("twindb"), "{collision:?}");
        assert!(collision.fix.contains("name no other platform answers to"), "{collision:?}");
        assert!(
            !mentions(&report, "does not resolve"),
            "a collision is not an unregistered platform:\n{report}"
        );
    }

    /// A platform reached under its own name owes nothing, whatever the case or
    /// the surrounding whitespace, and a name nothing has ever heard of is
    /// simply unknown rather than a finding against this dialect.
    #[test]
    fn registration_is_silent_on_a_platform_reached_under_its_own_name() {
        let mut registry = crate::dialect::PlatformRegistry::new();
        registry.register("healthydb".to_owned(), std::sync::Arc::new(HealthyPlugin::new()));

        let mut findings = Vec::new();
        check_registration(&HealthyPlugin::new().info(), &registry, &mut findings);
        assert!(findings.is_empty(), "{findings:?}");

        for spelling in ["healthydb", "HealthyDB", "  healthydb  "] {
            assert!(
                crate::resolve::resolve_dialect_by_name_with_registry(spelling, &registry).is_ok(),
                "'{spelling}' is the same platform"
            );
        }
        assert!(
            crate::resolve::resolve_dialect_by_name_with_registry("nosuchdb", &registry).is_err()
        );
    }

    /// **A dialect the host loaded at run time can be graded at all.** [`check`]
    /// asks the dialects linked into this program, which one loaded from a
    /// shared library is not among; [`check_with_registry`] asks the registry it
    /// was loaded into, and the registration judgement is answered from there.
    #[test]
    fn a_dialect_the_host_loaded_reports_clean_against_its_own_registry() {
        let mut registry = crate::dialect::PlatformRegistry::new();
        registry.register("healthydb".to_owned(), std::sync::Arc::new(HealthyPlugin::new()));

        let report = check_with_registry(&HealthyPlugin::new(), &registry);
        assert!(
            report.is_clean(),
            "a loaded dialect that answered everything owes nothing:\n{report}"
        );
    }

    /// **Every fix an outside author can read is a fix in their own crate.** A
    /// report that names a file inside Razeri is telling an author to edit a
    /// tree they do not have, and the fix cannot be performed at all.
    #[test]
    fn no_fix_line_sends_an_author_into_razeris_own_tree() {
        let mut collided = crate::dialect::PlatformRegistry::new();
        collided.register("healthydb".to_owned(), std::sync::Arc::new(HealthyPlugin::new()));
        collided.register("twindb".to_owned(), std::sync::Arc::new(Twin));

        let mut fixes: Vec<String> = Vec::new();
        for report in [
            check(&BrokenPlugin),
            check(&HealthyPlugin::new()),
            check(&OutsidePlugin::new()),
            // The collision and the unregistered-name judgements, which are the
            // two registration findings an author can actually reach.
            check_with_registry(&Twin, &collided),
            check_with_registry(&Twin, &crate::dialect::PlatformRegistry::new()),
        ] {
            fixes.extend(report.findings.iter().map(|f| f.fix.clone()));
        }
        assert!(fixes.len() >= 10, "the sweep reached the findings: {}", fixes.len());
        for fix in &fixes {
            for path in ["schemas/", "crates/", ".json", "scripts/", "razeri-design"] {
                assert!(
                    !fix.contains(path),
                    "a fix line names `{path}`, which is not in the author's crate:\n  {fix}"
                );
            }
        }
    }

    /// **A dialect that claims its own grammar and does not spell it is
    /// blocking**, and the finding names the method it owes.
    ///
    /// `Custom` is a promise that the dialect renders the routine itself, and
    /// Razeri keeps its side by writing nothing: no near-neighbour grammar,
    /// which fails on deploy, and no refusal, which would tell an author their
    /// engine has no routines when it has a whole language. A promise with
    /// nothing behind it is therefore a build that stops, and it has to be
    /// findable before the deploy rather than during it.
    #[test]
    fn a_custom_grammar_without_a_render_method_is_blocking_on_all_three_kinds() {
        for (kind, form_method, render_method) in [
            (RoutineKind::Procedure, "procedure_form", "render_procedure"),
            (RoutineKind::ScalarFunction, "scalar_function_form", "render_scalar_function"),
            (RoutineKind::TableFunction, "table_function_form", "render_table_function"),
        ] {
            let mut promised = Vec::new();
            check_custom_grammar(
                CustomGrammar {
                    kind,
                    grammar: "PL/SQL",
                    form_method,
                    render_method,
                    noun: "routines",
                },
                |_| None,
                &mut promised,
            );
            assert_eq!(promised.len(), 1, "{form_method}: {promised:?}");
            assert_eq!(promised[0].severity, Severity::Blocking, "{promised:?}");
            assert!(promised[0].what.contains(form_method), "{promised:?}");
            assert!(promised[0].what.contains("PL/SQL"), "{promised:?}");
            assert!(promised[0].fix.contains(render_method), "{promised:?}");

            // The same claim, kept: nothing to report.
            let mut kept = Vec::new();
            check_custom_grammar(
                CustomGrammar {
                    kind,
                    grammar: "PL/SQL",
                    form_method,
                    render_method,
                    noun: "routines",
                },
                |spec| Some(format!("CREATE {} …", spec.name)),
                &mut kept,
            );
            assert!(kept.is_empty(), "{form_method}: a kept promise is not a finding: {kept:?}");
        }
    }

    /// **A render method that answers with nothing at all is the same defect.**
    ///
    /// An override that returns an empty string is a routine razeri would emit
    /// as blank space in the middle of a schema, which is worse than an error:
    /// nothing in the deploy says anything is missing.
    #[test]
    fn a_custom_render_method_that_returns_nothing_is_blocking() {
        let mut findings = Vec::new();
        check_custom_grammar(
            CustomGrammar {
                kind: RoutineKind::Procedure,
                grammar: "PL/SQL",
                form_method: "procedure_form",
                render_method: "render_procedure",
                noun: "procedures",
            },
            |_| Some("   \n".to_owned()),
            &mut findings,
        );
        assert_eq!(findings.len(), 1, "{findings:?}");
        assert_eq!(findings[0].severity, Severity::Blocking, "{findings:?}");
    }

    /// **A `Custom` grammar with no name gives a reader nothing to read.**
    #[test]
    fn a_custom_grammar_with_no_name_is_blocking() {
        let mut findings = Vec::new();
        check_custom_grammar(
            CustomGrammar {
                kind: RoutineKind::ScalarFunction,
                grammar: "  ",
                form_method: "scalar_function_form",
                render_method: "render_scalar_function",
                noun: "scalar functions",
            },
            |spec| Some(format!("CREATE FUNCTION {}", spec.name)),
            &mut findings,
        );
        assert_eq!(findings.len(), 1, "{findings:?}");
        assert!(findings[0].what.contains("names no grammar"), "{findings:?}");
    }

    /// **A stated fact that is empty, and a stated fact that ignores its
    /// argument.**
    ///
    /// Both answers deploy without an error and are wrong in the data: an empty
    /// helper body keys every row to nothing, and a file relation that drops
    /// its path reads one file for every entity a design binds. Neither is
    /// visible anywhere else, which is why the kit grades them.
    #[test]
    fn a_stated_key_body_that_is_blank_and_a_file_relation_that_drops_its_path_are_blocking() {
        struct Overstated;
        impl SqlRenderer for Overstated {
            fn render_data_type(&self, dt: &DataType) -> String {
                razeri_plugin_contract::agnostic::render_data_type_ansi(dt)
            }
            fn quote_identifier(&self, name: &str) -> String {
                format!("\"{name}\"")
            }
            fn qualify_name(&self, _schema: Option<&str>, name: &str) -> String {
                name.to_owned()
            }
            fn render_current_timestamp(&self) -> String {
                "CURRENT_TIMESTAMP".to_owned()
            }
            fn dialect_name(&self) -> &'static str {
                "overstateddb"
            }
            fn sid_helper_body(&self) -> Option<razeri_plugin_contract::SidHelperBody> {
                Some(razeri_plugin_contract::SidHelperBody {
                    language: razeri_plugin_contract::SidHelperLanguage::JavaScript,
                    body: "   \n  ",
                })
            }
            fn delimited_file_relation(&self, _path_literal: &str) -> Option<String> {
                Some("read_csv_auto('/tmp/whatever.csv')".to_owned())
            }
        }
        impl ExpressionRenderer for Overstated {}
        impl DdlRenderer for Overstated {}
        impl DmlRenderer for Overstated {}
        impl ProcedureRenderer for Overstated {}
        impl FormulaRenderer for Overstated {}
        impl TaskRenderer for Overstated {}
        impl ReplicationRenderer for Overstated {}
        impl StorageRenderer for Overstated {}
        impl DialectCapabilities for Overstated {}
        impl PlatformDialect for Overstated {
            fn info(&self) -> DialectInfo {
                DialectInfo {
                    name: "overstateddb",
                    display_name: "Overstated DB",
                    aliases: &[],
                    dialect_family: DialectFamily::Custom(""),
                    family: "Overstated",
                    is_cloud_native: false,
                    is_olap: false,
                    is_postgres_compatible: false,
                }
            }
        }

        let report = check(&Overstated);
        for (fragment, why) in [
            ("supplies an empty one", "a blank helper body"),
            ("does not carry the path", "a file relation that drops its path"),
        ] {
            let found = report
                .findings
                .iter()
                .find(|f| f.what.contains(fragment))
                .unwrap_or_else(|| panic!("{why} is not graded:\n{report}"));
            assert_eq!(found.severity, Severity::Blocking, "{why}: {found:?}");
        }

        // And silence is not a finding. The fully-answered fixture states
        // neither fact — the majority answer — and owes nothing for it.
        let quiet = check(&HealthyPlugin::new());
        for fragment in ["supplies an empty one", "does not carry the path"] {
            assert!(
                !quiet.findings.iter().any(|f| f.what.contains(fragment)),
                "silence is the default and owes nothing:\n{quiet}"
            );
        }
    }

    /// **A stated refusal is a claim, and a claim owes the reader words** — the
    /// same grading every other refusal gets, because these words are the only
    /// thing an operator finds where the load would have been.
    #[test]
    fn a_stated_upsert_refusal_is_graded_as_copy_and_a_silent_one_as_unanswered() {
        let mut mute = Vec::new();
        check_refusal_copy("the upsert refusal", "no merge", &mut mute);
        assert_eq!(mute.len(), 1, "a three-word refusal is a wall: {mute:?}");
        assert!(mute[0].what.contains("the upsert refusal"), "{mute:?}");

        let silence = check(&BrokenPlugin);
        assert!(
            silence
                .findings
                .iter()
                .any(|f| f.severity == Severity::Unanswered && f.what.contains("upsert shape")),
            "a dialect that never answered is unanswered, not wrong:\n{silence}"
        );
        assert!(
            silence.findings.iter().any(|f| f.fix.contains("MergeShape::Unsupported")),
            "the fix line names the way to state a measured refusal:\n{silence}"
        );
    }

    /// The report leads with what to fix and says it in words a reader can
    /// act on — no identifiers from Razeri's own record-keeping, and a
    /// one-line count before the detail.
    #[test]
    fn the_report_reads_as_a_summary_then_a_fix_list() {
        let text = check(&BrokenPlugin).to_string();
        let first = text.lines().next().expect("a summary line");
        assert!(first.starts_with("brokendb:"), "{first}");
        assert!(first.contains("to fix"), "{first}");
        assert!(text.contains("      → "), "every finding names the fix:\n{text}");
    }
}