asciidoc_parser/parser/

parser.rs

use std::{
    cell::{Cell, RefCell},
    collections::{HashMap, HashSet},
    rc::Rc,
    sync::Arc,
};

use crate::{
    Document, HasSpan,
    blocks::{SectionNumber, SectionType},
    document::{Attribute, Catalog, InterpretedValue, RefType},
    parser::{
        AllowableValue, AttributeValue, DocinfoFileHandler, HtmlSubstitutionRenderer,
        IncludeFileHandler, InlineSubstitutionRenderer, ModificationContext, PathResolver,
        built_in_attrs::{built_in_attrs, built_in_default_values},
        preprocessor::preprocess,
    },
    warnings::{Warning, WarningType},
};

/// The [`Parser`] struct and its related structs allow a caller to configure
/// how AsciiDoc parsing occurs and then to initiate the parsing process.
#[derive(Clone, Debug)]
pub struct Parser {
    /// Attribute values at current state of parsing.
    ///
    /// Shared (copy-on-write via [`Arc`]) with the immutable built-in attribute
    /// table, so creating or cloning a parser does not deep-copy the table; the
    /// map is only copied the first time this parser modifies an attribute.
    pub(crate) attribute_values: Arc<HashMap<String, AttributeValue>>,

    /// Default values for attributes if "set." Immutable after construction and
    /// shared via [`Arc`] (never copied per parser).
    default_attribute_values: Arc<HashMap<String, String>>,

    /// Specifies how the basic raw text of a simple block will be converted to
    /// the format which will ultimately be presented in the final output.
    ///
    /// Typically this is an [`HtmlSubstitutionRenderer`] but clients may
    /// provide alternative implementations.
    pub(crate) renderer: Rc<dyn InlineSubstitutionRenderer>,

    /// Specifies the name of the primary file to be parsed.
    pub(crate) primary_file_name: Option<String>,

    /// Specifies how to generate clean and secure paths relative to the parsing
    /// context.
    pub path_resolver: PathResolver,

    /// Handler for resolving include:: directives.
    pub(crate) include_file_handler: Option<Rc<dyn IncludeFileHandler>>,

    /// Handler for resolving docinfo files. If absent, no docinfo content is
    /// resolved.
    pub(crate) docinfo_file_handler: Option<Rc<dyn DocinfoFileHandler>>,

    /// Document catalog for tracking referenceable elements during parsing.
    /// This is created during parsing and transferred to the Document when
    /// complete.
    ///
    /// Wrapped in a [`RefCell`] so that anchors and references discovered deep
    /// inside inline substitution (where only a shared `&Parser` is available,
    /// e.g. within a regex [`Replacer`](regex::Replacer)) can still be
    /// registered.
    catalog: RefCell<Catalog>,

    /// Most recently-assigned section number.
    pub(crate) last_section_number: SectionNumber,

    /// Most recently-assigned appendix section number.
    pub(crate) last_appendix_section_number: SectionNumber,

    /// Saved copy of sectnumlevels at end of document header.
    pub(crate) sectnumlevels: usize,

    /// Section type of outermost section. (Used to determine whether to number
    /// child sections as a normal section or appendix.)
    pub(crate) topmost_section_type: SectionType,

    /// True while parsing the direct block children of a section that carries
    /// the `bibliography` style.
    ///
    /// A top-level unordered list parsed in this scope implicitly inherits the
    /// `bibliography` style (matching Asciidoctor), even without its own
    /// `[bibliography]` attribute. The flag is saved and restored around each
    /// section body, so a non-bibliography subsection clears it for its own
    /// children (the style does not propagate into subsections).
    pub(crate) parsing_bibliography_section_body: bool,

    /// True while the principal text of a bibliography list item is being
    /// substituted.
    ///
    /// Read through a shared `&Parser` by the macros substitution step so it
    /// recognizes a leading bibliography anchor (`[[[id]]]`). It is wrapped in
    /// a [`Cell`] because the substitution code paths (e.g. a regex
    /// [`Replacer`](regex::Replacer)) only hold a shared reference to the
    /// parser.
    pub(crate) in_bibliography_list_item: Cell<bool>,

    /// Live values of [counter] attributes, keyed by counter name (e.g.
    /// `index`, `example-number`, `table-number`).
    ///
    /// A counter is a specialized document attribute: its value is *also* the
    /// value of the document attribute of the same name. Counters are resolved
    /// (and advanced) deep inside the attribute-reference substitution step,
    /// where only a shared `&Parser` is available, so the new value is recorded
    /// here through a [`RefCell`] and read back as an attribute by
    /// [`attribute_value()`]. An explicit attribute assignment to a counter's
    /// name supersedes this overlay (and is what allows `:!name:` to reset a
    /// counter), so every attribute setter clears the matching entry.
    ///
    /// Captioned blocks (example, table, …) are numbered with this same
    /// mechanism: each context's caption number is the counter named
    /// `<context>-number`, mirroring Asciidoctor's `Document#counter`.
    ///
    /// [counter]: https://docs.asciidoctor.org/asciidoc/latest/attributes/counters/
    /// [`attribute_value()`]: Self::attribute_value
    pub(crate) counter_values: RefCell<HashMap<String, String>>,

    /// Canonical names of attributes that are locked against modification from
    /// the document body for the current scope.
    ///
    /// An AsciiDoc table cell creates a nested document that inherits the
    /// parent document's attributes. An attribute that is *set* in the
    /// parent _cannot_ be modified inside the cell (matching Asciidoctor,
    /// which here diverges from the spec's "set or explicitly unset" wording),
    /// so while a cell is being parsed every inherited attribute name
    /// (other than a handful of exceptions) is recorded here and a body
    /// attribute assignment to such a name is silently ignored. The set is
    /// saved and restored around each cell, so the lock applies only within
    /// the cell (and nests correctly).
    pub(crate) locked_attribute_names: HashSet<String>,

    /// Number of AsciiDoc table cells currently being parsed in the call stack.
    ///
    /// An AsciiDoc table cell creates a nested, standalone AsciiDoc document.
    /// While that document is being parsed this counter is greater than zero,
    /// which (matching Asciidoctor's `Document#nested?`) changes the default
    /// cell separator of any table found inside from the vertical bar (`|`) to
    /// the exclamation mark (`!`), so a nested table needs no explicit
    /// `separator` attribute. The counter is incremented and decremented around
    /// each AsciiDoc cell, so it nests correctly.
    pub(crate) nested_document_depth: usize,

    /// Catalog of callout numbers registered by verbatim blocks, used to
    /// validate the callout lists that annotate them.
    ///
    /// Wrapped in a [`RefCell`] because callouts are registered deep inside the
    /// callouts substitution step, where only a shared `&Parser` is available.
    callouts: RefCell<CalloutCatalog>,

    /// Warnings produced while replacing attribute references (e.g. a reference
    /// to a missing attribute when `attribute-missing` is `warn`).
    ///
    /// Wrapped in a [`RefCell`] because attribute references are replaced deep
    /// inside the attributes substitution step, where only a shared `&Parser`
    /// is available. Each entry stores the byte offset and length of the source
    /// span the warning refers to (rather than a borrowed
    /// [`Span`](crate::Span), which the lifetime-free `Parser` cannot
    /// hold), so the warnings can be turned into
    /// spanned [`Warning`]s once the document's owned source is available.
    substitution_warnings: RefCell<Vec<SubstitutionWarning>>,
}

/// A warning recorded while replacing attribute references, stored in a form
/// that does not borrow the source so it can live on the [`Parser`].
///
/// The `offset`/`len` pair locates the relevant text within the (preprocessed)
/// document source; [`Parser::take_substitution_warnings`] reconstitutes a
/// spanned [`Warning`] from it.
#[derive(Clone, Debug)]
pub(crate) struct SubstitutionWarning {
    /// Byte offset into the document source of the span this warning refers to.
    pub(crate) offset: usize,

    /// Byte length of the span this warning refers to.
    pub(crate) len: usize,

    /// The type of warning, already carrying any owned data it needs (such as
    /// the missing attribute's name).
    pub(crate) warning: WarningType,
}

/// Tracks the callout numbers defined by verbatim blocks so that a callout list
/// can be validated against the callouts it annotates.
///
/// This mirrors the relevant behavior of Asciidoctor's `Callouts` catalog: each
/// verbatim block registers the callout numbers it defines into the current
/// list, and each callout list checks its items against that list (warning
/// about any item with no matching callout) before the list is closed.
#[derive(Clone, Debug, Default)]
struct CalloutCatalog {
    /// Callout numbers registered (in document order) since the last callout
    /// list was closed.
    current: Vec<u32>,
}

impl Default for Parser {
    fn default() -> Self {
        Self {
            attribute_values: built_in_attrs(),
            default_attribute_values: built_in_default_values(),
            renderer: Rc::new(HtmlSubstitutionRenderer {}),
            primary_file_name: None,
            path_resolver: PathResolver::default(),
            include_file_handler: None,
            docinfo_file_handler: None,
            catalog: RefCell::new(Catalog::new()),
            last_section_number: SectionNumber::default(),
            last_appendix_section_number: SectionNumber {
                section_type: SectionType::Appendix,
                components: vec![],
            },
            sectnumlevels: 3,
            topmost_section_type: SectionType::Normal,
            parsing_bibliography_section_body: false,
            in_bibliography_list_item: Cell::new(false),
            counter_values: RefCell::new(HashMap::new()),
            locked_attribute_names: HashSet::new(),
            nested_document_depth: 0,
            callouts: RefCell::new(CalloutCatalog::default()),
            substitution_warnings: RefCell::new(vec![]),
        }
    }
}

impl Parser {
    /// Parse a UTF-8 string as an AsciiDoc document.
    ///
    /// The [`Document`] data structure returned by this call has a '`static`
    /// lifetime; this is an implementation detail. It retains a copy of the
    /// `source` string that was passed in, but it is not tied to the lifetime
    /// of that string.
    ///
    /// Nearly all of the data structures contained within the [`Document`]
    /// structure are tied to the lifetime of the document and have a `'src`
    /// lifetime to signal their dependency on the source document.
    ///
    /// **IMPORTANT:** The AsciiDoc language documentation states that UTF-16
    /// encoding is allowed if a byte-order-mark (BOM) is present at the
    /// start of a file. This format is not directly supported by the
    /// `asciidoc-parser` crate. Any UTF-16 content must be re-encoded as
    /// UTF-8 prior to parsing.
    ///
    /// The `Parser` struct will be updated with document attribute values
    /// discovered during parsing. These values may be inspected using
    /// [`attribute_value()`].
    ///
    /// # Warnings, not errors
    ///
    /// Any UTF-8 string is a valid AsciiDoc document, so this function does not
    /// return an [`Option`] or [`Result`] data type. There may be any number of
    /// character sequences that have ambiguous or potentially unintended
    /// meanings. For that reason, a caller is advised to review the warnings
    /// provided via the [`warnings()`] iterator.
    ///
    /// [`warnings()`]: Document::warnings
    /// [`attribute_value()`]: Self::attribute_value
    pub fn parse(&mut self, source: &str) -> Document<'static> {
        let mut document = self.parse_deferred(source);

        // Resolve cross-references against this document's own catalog. For
        // multi-document workflows, use `parse_deferred` and resolve later with
        // a caller-supplied resolver via `Document::resolve_references`.
        document.resolve_against_own_catalog(&*self.renderer);

        document
    }

    /// Parse a UTF-8 string as an AsciiDoc document, leaving cross-references
    /// unresolved.
    ///
    /// This behaves like [`parse()`], except it does not resolve
    /// cross-references (`<<id>>`, `xref:id[…]`). The returned [`Document`]
    /// carries its references in a deferred state; resolve them later with
    /// [`Document::resolve_references`].
    ///
    /// This is the entry point for multi-document workflows (e.g. Antora-style
    /// site generation): parse every document with this method, build a
    /// combined index from each document's [`catalog()`], then resolve each
    /// document against that index. This crate does not merge catalogs
    /// itself.
    ///
    /// [`parse()`]: Self::parse
    /// [`catalog()`]: Document::catalog
    pub fn parse_deferred(&mut self, source: &str) -> Document<'static> {
        let (preprocessed_source, source_map) = preprocess(source, self);

        // NOTE: `Document::parse` will transfer the catalog to itself at the end of the
        // parsing operation. Start each parse with a fresh catalog.
        *self.catalog.borrow_mut() = Catalog::new();

        // Start each parse with an empty callout catalog.
        *self.callouts.borrow_mut() = CalloutCatalog::default();

        // Start each parse with no pending substitution warnings.
        self.substitution_warnings.borrow_mut().clear();

        // Reset section numbering for each new document.
        self.last_section_number = SectionNumber::default();

        // Reset counter (and captioned-block) numbering for each new document.
        self.counter_values.borrow_mut().clear();

        Document::parse(&preprocessed_source, source_map, self)
    }

    /// Retrieves the current interpreted value of a [document attribute].
    ///
    /// Each document holds a set of name-value pairs called document
    /// attributes. These attributes provide a means of configuring the AsciiDoc
    /// processor, declaring document metadata, and defining reusable content.
    /// This page introduces document attributes and answers some questions
    /// about the terminology used when referring to them.
    ///
    /// ## What are document attributes?
    ///
    /// Document attributes are effectively document-scoped variables for the
    /// AsciiDoc language. The AsciiDoc language defines a set of built-in
    /// attributes, and also allows the author (or extensions) to define
    /// additional document attributes, which may replace built-in attributes
    /// when permitted.
    ///
    /// Built-in attributes either provide access to read-only information about
    /// the document and its environment or allow the author to configure
    /// behavior of the AsciiDoc processor for a whole document or select
    /// regions. Built-in attributes are effectively unordered. User-defined
    /// attribute serve as a powerful text replacement tool. User-defined
    /// attributes are stored in the order in which they are defined.
    ///
    /// [document attribute]: https://docs.asciidoctor.org/asciidoc/latest/attributes/document-attributes/
    pub fn attribute_value<N: AsRef<str>>(&self, name: N) -> InterpretedValue {
        // A counter's current value lives in the overlay and supersedes any
        // earlier value of the attribute of the same name (see
        // [`counter_values`](Self::counter_values)).
        if let Some(value) = self.counter_values.borrow().get(name.as_ref()) {
            return InterpretedValue::Value(value.clone());
        }

        self.attribute_values
            .get(name.as_ref())
            .map(|av| av.value.clone())
            .map(|av| {
                if let InterpretedValue::Set = av
                    && let Some(default) = self.default_attribute_values.get(name.as_ref())
                {
                    InterpretedValue::Value(default.clone())
                } else {
                    av
                }
            })
            .unwrap_or(InterpretedValue::Unset)
    }

    /// Returns `true` if the parser has a [document attribute] by this name.
    ///
    /// [document attribute]: https://docs.asciidoctor.org/asciidoc/latest/attributes/document-attributes/
    pub fn has_attribute<N: AsRef<str>>(&self, name: N) -> bool {
        self.counter_values.borrow().contains_key(name.as_ref())
            || self.attribute_values.contains_key(name.as_ref())
    }

    /// Returns `true` if the parser has a [document attribute] by this name
    /// which has been set (i.e. is present and not [unset]).
    ///
    /// [document attribute]: https://docs.asciidoctor.org/asciidoc/latest/attributes/document-attributes/
    /// [unset]: https://docs.asciidoctor.org/asciidoc/latest/attributes/unset-attributes/
    pub fn is_attribute_set<N: AsRef<str>>(&self, name: N) -> bool {
        // A counter always holds a concrete (set) value.
        if self.counter_values.borrow().contains_key(name.as_ref()) {
            return true;
        }

        self.attribute_values
            .get(name.as_ref())
            .map(|a| a.value != InterpretedValue::Unset)
            .unwrap_or(false)
    }

    /// Resolves whether a document title should be displayed, from the
    /// `showtitle`/`notitle` attribute pair (which are complements).
    ///
    /// `showtitle` takes precedence: if present, the title shows precisely when
    /// it is set. Otherwise `notitle`, if present, hides the title when set.
    /// When neither attribute is present, `default_shown` decides — a
    /// standalone document (such as a nested AsciiDoc table cell) shows its
    /// title, while an embedded document does not.
    pub(crate) fn resolve_show_title(&self, default_shown: bool) -> bool {
        if self.has_attribute("showtitle") {
            self.is_attribute_set("showtitle")
        } else if self.has_attribute("notitle") {
            !self.is_attribute_set("notitle")
        } else {
            default_shown
        }
    }

    /// Forces the `doctype` attribute to `value`, refreshing the derived
    /// `backend-html5-doctype-*` attribute.
    ///
    /// Used when a nested AsciiDoc table cell resets its doctype to the default
    /// (a cell does not inherit the parent's doctype). The value stays
    /// modifiable from the document body so the cell may still set its own
    /// doctype.
    pub(crate) fn force_doctype(&mut self, value: &str) {
        Arc::make_mut(&mut self.attribute_values).insert(
            "doctype".to_string(),
            AttributeValue {
                allowable_value: AllowableValue::Any,
                modification_context: ModificationContext::ApiOrDocumentBody,
                value: InterpretedValue::Value(value.to_string()),
            },
        );
        self.refresh_doctype_derived_attr();
    }

    /// Recomputes the `backend-html5-doctype-{doctype}` intrinsic attribute so
    /// exactly one exists — for the active doctype — resolving to an empty
    /// (defined) value. References to any other doctype stay undefined and so
    /// render literally.
    pub(crate) fn refresh_doctype_derived_attr(&mut self) {
        Arc::make_mut(&mut self.attribute_values)
            .retain(|name, _| !name.starts_with("backend-html5-doctype-"));

        if let InterpretedValue::Value(doctype) = self.attribute_value("doctype") {
            Arc::make_mut(&mut self.attribute_values).insert(
                format!("backend-html5-doctype-{doctype}"),
                AttributeValue {
                    allowable_value: AllowableValue::Any,
                    modification_context: ModificationContext::Anywhere,
                    value: InterpretedValue::Value(String::new()),
                },
            );
        }
    }

    /// Sets the value of an [intrinsic attribute].
    ///
    /// Intrinsic attributes are set automatically by the processor. These
    /// attributes provide information about the document being processed (e.g.,
    /// `docfile`), the security mode under which the processor is running
    /// (e.g., `safe-mode-name`), and information about the user’s environment
    /// (e.g., `user-home`).
    ///
    /// The [`modification_context`](ModificationContext) establishes whether
    /// the value can be subsequently modified by the document header and/or in
    /// the document body.
    ///
    /// Subsequent calls to this function or [`with_intrinsic_attribute_bool()`]
    /// are always permitted. The last such call for any given attribute name
    /// takes precendence.
    ///
    /// [intrinsic attribute]: https://docs.asciidoctor.org/asciidoc/latest/attributes/document-attributes-ref/#intrinsic-attributes
    ///
    /// [`with_intrinsic_attribute_bool()`]: Self::with_intrinsic_attribute_bool
    pub fn with_intrinsic_attribute<N: AsRef<str>, V: AsRef<str>>(
        mut self,
        name: N,
        value: V,
        modification_context: ModificationContext,
    ) -> Self {
        let attribute_value = AttributeValue {
            allowable_value: AllowableValue::Any,
            modification_context,
            value: InterpretedValue::Value(value.as_ref().to_string()),
        };

        Arc::make_mut(&mut self.attribute_values)
            .insert(name.as_ref().to_lowercase(), attribute_value);

        self
    }

    /// Register a referenceable element (anchor, section, bibliography entry)
    /// in the document catalog.
    ///
    /// This takes `&self` (rather than `&mut self`) so that it can be called
    /// from inline-substitution code paths that only hold a shared reference to
    /// the parser, such as a regex [`Replacer`](regex::Replacer).
    pub(crate) fn register_ref(
        &self,
        id: &str,
        reftext: Option<&str>,
        ref_type: RefType,
    ) -> Result<(), crate::document::DuplicateIdError> {
        self.catalog
            .borrow_mut()
            .register_ref(id, reftext, ref_type)
    }

    /// Registers a callout number defined by a verbatim block.
    ///
    /// Takes `&self` so it can be called from the callouts substitution step,
    /// which only holds a shared reference to the parser.
    pub(crate) fn register_callout(&self, number: u32) {
        self.callouts.borrow_mut().current.push(number);
    }

    /// Returns `true` if a callout numbered `number` was registered for the
    /// current (not-yet-closed) callout list.
    pub(crate) fn callout_defined(&self, number: u32) -> bool {
        self.callouts.borrow().current.contains(&number)
    }

    /// Closes the current callout list, so callouts registered afterward belong
    /// to the next list.
    pub(crate) fn close_callout_list(&self) {
        self.callouts.borrow_mut().current.clear();
    }

    /// Records a warning produced while replacing attribute references.
    ///
    /// Takes `&self` so it can be called from the attributes substitution step,
    /// which only holds a shared reference to the parser. `source` locates the
    /// text the warning refers to; its byte offset and length are stored so a
    /// spanned [`Warning`] can be reconstructed later (see
    /// [`take_substitution_warnings`](Self::take_substitution_warnings)).
    pub(crate) fn record_substitution_warning(
        &self,
        source: crate::Span<'_>,
        warning: WarningType,
    ) {
        self.substitution_warnings
            .borrow_mut()
            .push(SubstitutionWarning {
                offset: source.byte_offset(),
                len: source.len(),
                warning,
            });
    }

    /// Returns the number of substitution warnings recorded so far.
    ///
    /// Used together with [`truncate_substitution_warnings`] to discard
    /// warnings recorded while parsing an owned (e.g. include-expanded) source,
    /// whose offsets do not refer to the primary document source.
    ///
    /// [`truncate_substitution_warnings`]: Self::truncate_substitution_warnings
    pub(crate) fn substitution_warnings_len(&self) -> usize {
        self.substitution_warnings.borrow().len()
    }

    /// Discards any substitution warnings recorded since the buffer held `len`
    /// entries.
    pub(crate) fn truncate_substitution_warnings(&self, len: usize) {
        self.substitution_warnings.borrow_mut().truncate(len);
    }

    /// Takes the substitution warnings recorded during parsing, leaving the
    /// buffer empty.
    pub(crate) fn take_substitution_warnings(&self) -> Vec<SubstitutionWarning> {
        std::mem::take(&mut *self.substitution_warnings.borrow_mut())
    }

    /// Generate a unique ID derived from `base_id` and register it in the
    /// document catalog, returning the ID that was assigned.
    pub(crate) fn generate_and_register_unique_id(
        &self,
        base_id: &str,
        reftext: Option<&str>,
        ref_type: RefType,
    ) -> String {
        self.catalog
            .borrow_mut()
            .generate_and_register_unique_id(base_id, reftext, ref_type)
    }

    /// Takes the catalog from the parser, transferring ownership and leaving an
    /// empty catalog in its place.
    ///
    /// This is used by `Document::parse` to transfer the catalog from the
    /// parser to the document at the end of parsing.
    pub(crate) fn take_catalog(&mut self) -> Catalog {
        std::mem::take(&mut *self.catalog.borrow_mut())
    }

    /* Comment out until we're prepared to use and test this.
        /// Sets the default value for an [intrinsic attribute].
        ///
        /// Default values for attributes are provided automatically by the
        /// processor. These values provide a falllback textual value for an
        /// attribute when it is merely "set" by the document via API, header, or
        /// document body.
        ///
        /// Calling this does not imply that the value is set automatically by
        /// default, nor does it establish any policy for where the value may be
        /// modified. For that, please use [`with_intrinsic_attribute`].
        ///
        /// [intrinsic attribute]: https://docs.asciidoctor.org/asciidoc/latest/attributes/document-attributes-ref/#intrinsic-attributes
        /// [`with_intrinsic_attribute`]: Self::with_intrinsic_attribute
        pub fn with_default_attribute_value<N: AsRef<str>, V: AsRef<str>>(
            mut self,
            name: N,
            value: V,
        ) -> Self {
            self.default_attribute_values
                .insert(name.as_ref().to_string(), value.as_ref().to_string());

            self
        }
    */

    /// Sets the value of an [intrinsic attribute] from a boolean flag.
    ///
    /// A boolean `true` is interpreted as "set." A boolean `false` is
    /// interpreted as "unset."
    ///
    /// Intrinsic attributes are set automatically by the processor. These
    /// attributes provide information about the document being processed (e.g.,
    /// `docfile`), the security mode under which the processor is running
    /// (e.g., `safe-mode-name`), and information about the user’s environment
    /// (e.g., `user-home`).
    ///
    /// The [`modification_context`](ModificationContext) establishes whether
    /// the value can be subsequently modified by the document header and/or in
    /// the document body.
    ///
    /// Subsequent calls to this function or [`with_intrinsic_attribute()`] are
    /// always permitted. The last such call for any given attribute name takes
    /// precendence.
    ///
    /// [intrinsic attribute]: https://docs.asciidoctor.org/asciidoc/latest/attributes/document-attributes-ref/#intrinsic-attributes
    ///
    /// [`with_intrinsic_attribute()`]: Self::with_intrinsic_attribute
    pub fn with_intrinsic_attribute_bool<N: AsRef<str>>(
        mut self,
        name: N,
        value: bool,
        modification_context: ModificationContext,
    ) -> Self {
        let attribute_value = AttributeValue {
            allowable_value: AllowableValue::Any,
            modification_context,
            value: if value {
                InterpretedValue::Set
            } else {
                InterpretedValue::Unset
            },
        };

        Arc::make_mut(&mut self.attribute_values)
            .insert(name.as_ref().to_lowercase(), attribute_value);

        self
    }

    /// Replace the default [`InlineSubstitutionRenderer`] for this parser.
    ///
    /// The default implementation of [`InlineSubstitutionRenderer`] that is
    /// provided is suitable for HTML5 rendering. If you are targeting a
    /// different back-end rendering, you will need to provide your own
    /// implementation and set it using this call before parsing.
    pub fn with_inline_substitution_renderer<ISR: InlineSubstitutionRenderer + 'static>(
        mut self,
        renderer: ISR,
    ) -> Self {
        self.renderer = Rc::new(renderer);
        self
    }

    /// Sets the name of the primary file to be parsed when [`parse()`] is
    /// called.
    ///
    /// This name will be used for any error messages detected in this file and
    /// also will be passed to [`IncludeFileHandler::resolve_target()`] as the
    /// `source` argument for any `include::` file resolution requests from this
    /// file.
    ///
    /// [`parse()`]: Self::parse
    /// [`IncludeFileHandler::resolve_target()`]: crate::parser::IncludeFileHandler::resolve_target
    pub fn with_primary_file_name<S: AsRef<str>>(mut self, name: S) -> Self {
        self.primary_file_name = Some(name.as_ref().to_owned());
        self
    }

    /// Sets the [`IncludeFileHandler`] for this parser.
    ///
    /// The include file handler is responsible for resolving `include::`
    /// directives encountered during preprocessing. If no handler is provided,
    /// include directives will be ignored.
    ///
    /// [`IncludeFileHandler`]: crate::parser::IncludeFileHandler
    pub fn with_include_file_handler<IFH: IncludeFileHandler + 'static>(
        mut self,
        handler: IFH,
    ) -> Self {
        self.include_file_handler = Some(Rc::new(handler));
        self
    }

    /// Sets the [`DocinfoFileHandler`] for this parser.
    ///
    /// The docinfo file handler is responsible for providing the content of
    /// [docinfo files] requested while resolving a document's docinfo (see the
    /// `docinfo` attribute). If no handler is provided, no docinfo content is
    /// resolved and [`Document::docinfo`] returns an empty string for every
    /// location.
    ///
    /// [`DocinfoFileHandler`]: crate::parser::DocinfoFileHandler
    /// [docinfo files]: https://docs.asciidoctor.org/asciidoc/latest/docinfo/
    /// [`Document::docinfo`]: crate::Document::docinfo
    pub fn with_docinfo_file_handler<DFH: DocinfoFileHandler + 'static>(
        mut self,
        handler: DFH,
    ) -> Self {
        self.docinfo_file_handler = Some(Rc::new(handler));
        self
    }

    /// Returns the document name (`docname`): the base name of the primary
    /// file, stripped of its directory and final extension.
    ///
    /// This is the `<docname>` used to build private docinfo file names (e.g.
    /// `mydoc-docinfo.html` for `mydoc.adoc`). Returns `None` when no primary
    /// file name has been set, in which case private docinfo files cannot be
    /// resolved.
    pub(crate) fn docname(&self) -> Option<String> {
        let primary = self.primary_file_name.as_deref()?;

        // Strip the directory portion (handling both separators, since the
        // primary file name may have been supplied on either platform).
        let base = primary.rsplit(['/', '\\']).next().unwrap_or(primary);

        // Strip a single trailing extension, if present. A leading-dot name
        // (e.g. `.adoc`) is treated as having no extension and is kept whole as
        // the stem, matching Ruby's `File.basename(".adoc", ".*")`.
        let stem = match base.rfind('.') {
            Some(0) | None => base,
            Some(idx) => &base[..idx],
        };

        if stem.is_empty() {
            None
        } else {
            Some(stem.to_string())
        }
    }

    /// Called from [`Header::parse()`] to accept or reject an attribute value.
    ///
    /// [`Header::parse()`]: crate::document::Header::parse
    pub(crate) fn set_attribute_from_header<'src>(
        &mut self,
        attr: &Attribute<'src>,
        warnings: &mut Vec<Warning<'src>>,
    ) {
        let attr_name = remap_attr_name(attr.name().data());

        let existing_attr = self.attribute_values.get(&attr_name);

        // Verify that we have permission to overwrite any existing attribute value.
        if let Some(existing_attr) = existing_attr
            && (existing_attr.modification_context == ModificationContext::ApiOnly
                || existing_attr.modification_context == ModificationContext::ApiOrDocumentBody)
        {
            warnings.push(Warning {
                source: attr.span(),
                warning: WarningType::AttributeValueIsLocked(attr_name),
            });
            return;
        }

        let mut value = attr.value().clone();

        if let InterpretedValue::Set = value
            && let Some(default_value) = self.default_attribute_values.get(&attr_name)
        {
            value = InterpretedValue::Value(default_value.clone());
        }

        let attribute_value = AttributeValue {
            allowable_value: AllowableValue::Any,
            modification_context: ModificationContext::Anywhere,
            value,
        };

        // An explicit assignment supersedes (and resets) any counter of the same
        // name.
        self.counter_values.borrow_mut().remove(&attr_name);

        let is_doctype = attr_name == "doctype";
        Arc::make_mut(&mut self.attribute_values).insert(attr_name, attribute_value);
        if is_doctype {
            self.refresh_doctype_derived_attr();
        }
    }

    /// Called from [`Header::parse()`] for a value that is derived from parsing
    /// the header (except for attribute lines).
    ///
    /// [`Header::parse()`]: crate::document::Header::parse
    pub(crate) fn set_attribute_by_value_from_header<N: AsRef<str>, V: AsRef<str>>(
        &mut self,
        name: N,
        value: V,
    ) {
        let attr_name = remap_attr_name(name);

        let attribute_value = AttributeValue {
            allowable_value: AllowableValue::Any,
            modification_context: ModificationContext::Anywhere,
            value: InterpretedValue::Value(value.as_ref().to_owned()),
        };

        self.counter_values.borrow_mut().remove(&attr_name);
        Arc::make_mut(&mut self.attribute_values).insert(attr_name, attribute_value);
    }

    /// Called while parsing a block (see [`Block::parse_with_outcome()`]) to
    /// accept or reject an attribute value from a document (body) attribute.
    ///
    /// [`Block::parse_with_outcome()`]: crate::blocks::Block::parse_with_outcome
    pub(crate) fn set_attribute_from_body<'src>(
        &mut self,
        attr: &Attribute<'src>,
        warnings: &mut Vec<Warning<'src>>,
    ) {
        let attr_name = remap_attr_name(attr.name().data());

        // An attribute inherited from the parent document of an AsciiDoc table
        // cell is locked for the duration of that cell: a body assignment to it
        // is silently ignored (no warning), matching Asciidoctor.
        if self.locked_attribute_names.contains(&attr_name) {
            return;
        }

        // Verify that we have permission to overwrite any existing attribute value.
        if let Some(existing_attr) = self.attribute_values.get(&attr_name)
            && (existing_attr.modification_context != ModificationContext::Anywhere
                && existing_attr.modification_context != ModificationContext::ApiOrDocumentBody)
        {
            warnings.push(Warning {
                source: attr.span(),
                warning: WarningType::AttributeValueIsLocked(attr_name),
            });
            return;
        }

        let attribute_value = AttributeValue {
            allowable_value: AllowableValue::Any,
            modification_context: ModificationContext::Anywhere,
            value: attr.value().clone(),
        };

        // An explicit assignment supersedes (and resets) any counter of the same
        // name. This is what lets `:!name:` reset a counter.
        self.counter_values.borrow_mut().remove(&attr_name);

        let is_doctype = attr_name == "doctype";
        Arc::make_mut(&mut self.attribute_values).insert(attr_name, attribute_value);
        if is_doctype {
            self.refresh_doctype_derived_attr();
        }
    }

    /// Assign the next section number for a given level.
    pub(crate) fn assign_section_number(&mut self, level: usize) -> SectionNumber {
        match self.topmost_section_type {
            SectionType::Normal => {
                self.last_section_number.assign_next_number(level);
                self.last_section_number.clone()
            }
            SectionType::Appendix => {
                self.last_appendix_section_number.assign_next_number(level);
                self.last_appendix_section_number.clone()
            }
            SectionType::Discrete => {
                // Shouldn't happen, but ignore if it does.
                self.last_section_number.clone()
            }
        }
    }

    /// Resolves a [counter] of the given `name`, advancing it to the next value
    /// in its sequence and returning that value.
    ///
    /// A counter is a specialized document attribute: its value is stored as
    /// (and read back from) the attribute of the same name, so a later
    /// `{name}` reference shows the current value and an attribute assignment
    /// such as `:!name:` resets it. Each resolution advances the counter:
    ///
    /// * an integer value is incremented (`1` -> `2`);
    /// * any other value is advanced like Ruby's `String#succ` (`a` -> `b`, `z`
    ///   -> `aa`, `Az` -> `Ba`), matching Asciidoctor.
    ///
    /// `seed` (from the `{counter:name:seed}` form) supplies the first value,
    /// but only when the counter is currently unset; otherwise it is ignored.
    /// With no seed the sequence starts at `1`.
    ///
    /// This mirrors Asciidoctor's `Document#counter`.
    ///
    /// [counter]: https://docs.asciidoctor.org/asciidoc/latest/attributes/counters/
    pub(crate) fn counter(&self, name: &str, seed: Option<&str>) -> String {
        let next = match self.attribute_value(name) {
            InterpretedValue::Value(current) if !current.is_empty() => next_counter_value(&current),
            _ => match seed {
                Some(seed) if !seed.is_empty() => seed.to_string(),
                _ => "1".to_string(),
            },
        };

        self.counter_values
            .borrow_mut()
            .insert(name.to_string(), next.clone());

        next
    }
}

/// Advances a counter value to the next value in its sequence, mirroring
/// Asciidoctor's `Helpers.nextval`.
///
/// A canonical integer string (one that round-trips through integer parsing,
/// e.g. `7` but not `07` or `+7`) is incremented numerically. Anything else is
/// advanced with [`string_succ`].
fn next_counter_value(current: &str) -> String {
    if let Ok(n) = current.parse::<i64>()
        && n.to_string() == current
    {
        // `saturating_add` keeps a counter that has somehow reached `i64::MAX`
        // pinned there rather than panicking (debug) or wrapping (release).
        return n.saturating_add(1).to_string();
    }

    string_succ(current)
}

/// Returns the successor of a string, mirroring Ruby's `String#succ` for the
/// ASCII cases that AsciiDoc counters can produce.
///
/// The right-most alphanumeric character is incremented within its own class
/// (digits, lowercase letters, uppercase letters), carrying leftward on
/// wrap-around (`9` -> `0`, `z` -> `a`, `Z` -> `A`) and prepending a fresh
/// leading character (`1`, `a`, or `A`) when the carry runs off the front
/// (`z` -> `aa`, `Zz` -> `AAa`). A string with no alphanumeric characters has
/// the code point of its last character incremented.
fn string_succ(current: &str) -> String {
    let chars: Vec<char> = current.chars().collect();

    // Without an alphanumeric to carry through, Ruby increments the code point
    // of the final character.
    if !chars.iter().any(char::is_ascii_alphanumeric) {
        let mut chars = chars;
        if let Some(last) = chars.last_mut() {
            *last = char::from_u32(*last as u32 + 1).unwrap_or(*last);
        }
        return chars.into_iter().collect();
    }

    // Walk right to left. `carrying` stays true while we are still looking for
    // (or carrying through) the alphanumeric run: trailing non-alphanumeric
    // characters are passed over unchanged, then the right-most alphanumeric is
    // incremented within its class and any wrap-around carries leftward to the
    // next alphanumeric. When the carry runs off the front, a fresh leading
    // character of the same class is prepended (`z` -> `aa`, `9` -> `10`).
    let mut out_rev: Vec<char> = Vec::with_capacity(chars.len() + 1);
    let mut carrying = true;
    let mut lead = '1';

    for &c in chars.iter().rev() {
        if carrying && c.is_ascii_alphanumeric() {
            // Increment within the character's class, carrying on wrap-around.
            // The arms are exhaustive over ASCII alphanumerics, so the catch-all
            // can only be `Z` (the one value not matched above).
            let (next, carry) = match c {
                '0'..='8' | 'a'..='y' | 'A'..='Y' => ((c as u8 + 1) as char, false),
                '9' => ('0', true),
                'z' => ('a', true),
                _ => ('A', true),
            };
            out_rev.push(next);
            carrying = carry;
            // On a carry, remember the class of leading character to prepend if
            // the carry runs off the front; `next` is `0`, `a`, or `A` here.
            lead = match next {
                '0' => '1',
                'a' => 'a',
                _ => 'A',
            };
        } else {
            // Either the carry is spent, or this is a trailing non-alphanumeric
            // we pass over while still searching for the run to increment.
            out_rev.push(c);
        }
    }

    if carrying {
        out_rev.push(lead);
    }

    out_rev.into_iter().rev().collect()
}

fn remap_attr_name<N: AsRef<str>>(raw_attr_name: N) -> String {
    let attr_name = raw_attr_name.as_ref().to_lowercase();

    // Some attribute names have aliases. Remap to the primary name.
    match attr_name.as_str() {
        "hardbreaks" => "hardbreaks-option".to_string(),
        _ => attr_name,
    }
}

#[cfg(test)]
mod tests {
    #![allow(clippy::panic)]
    #![allow(clippy::unwrap_used)]

    use crate::{
        attributes::Attrlist,
        blocks::Block,
        parser::{
            CharacterReplacementType, IconRenderParams, ImageRenderParams,
            InlineSubstitutionRenderer, LinkRenderParams, QuoteScope, QuoteType, SpecialCharacter,
        },
        tests::prelude::*,
    };

    #[test]
    fn default_is_unset() {
        let p = Parser::default();
        assert_eq!(p.attribute_value("foo"), InterpretedValue::Unset);
    }

    #[test]
    fn creates_catalog_if_needed() {
        let mut p = Parser::default();
        let doc = p.parse("= Hello, World!\n\n== First Section Title");
        let cat = doc.catalog();
        assert!(cat.refs.contains_key("_first_section_title"));

        let doc = p.parse("= Hello, World!\n\n== Second Section Title");
        let cat = doc.catalog();
        assert!(!cat.refs.contains_key("_first_section_title"));
        assert!(cat.refs.contains_key("_second_section_title"));
    }

    #[test]
    fn with_intrinsic_attribute() {
        let p =
            Parser::default().with_intrinsic_attribute("foo", "bar", ModificationContext::Anywhere);

        assert_eq!(p.attribute_value("foo"), InterpretedValue::Value("bar"));
        assert_eq!(p.attribute_value("foo2"), InterpretedValue::Unset);

        assert!(p.is_attribute_set("foo"));
        assert!(!p.is_attribute_set("foo2"));
        assert!(!p.is_attribute_set("xyz"));
    }

    #[test]
    fn with_intrinsic_attribute_set() {
        let p = Parser::default().with_intrinsic_attribute_bool(
            "foo",
            true,
            ModificationContext::Anywhere,
        );

        assert_eq!(p.attribute_value("foo"), InterpretedValue::Set);
        assert_eq!(p.attribute_value("foo2"), InterpretedValue::Unset);

        assert!(p.is_attribute_set("foo"));
        assert!(!p.is_attribute_set("foo2"));
        assert!(!p.is_attribute_set("xyz"));
    }

    #[test]
    fn with_intrinsic_attribute_unset() {
        let p = Parser::default().with_intrinsic_attribute_bool(
            "foo",
            false,
            ModificationContext::Anywhere,
        );

        assert_eq!(p.attribute_value("foo"), InterpretedValue::Unset);
        assert_eq!(p.attribute_value("foo2"), InterpretedValue::Unset);

        assert!(!p.is_attribute_set("foo"));
        assert!(!p.is_attribute_set("foo2"));
        assert!(!p.is_attribute_set("xyz"));
    }

    #[test]
    fn can_not_override_locked_default_value() {
        let mut parser = Parser::default();

        let doc = parser.parse(":sp: not a space!");

        assert_eq!(
            doc.warnings().next().unwrap().warning,
            WarningType::AttributeValueIsLocked("sp".to_owned())
        );

        assert_eq!(parser.attribute_value("sp"), InterpretedValue::Value(" "));
    }

    #[test]
    fn catalog_transferred_to_document() {
        let mut parser = Parser::default();
        let doc = parser.parse("= Test Document\n\nSome content");

        let catalog = doc.catalog();
        assert!(catalog.is_empty());

        // The catalog was transferred to the document, leaving the parser with
        // an empty catalog.
        assert!(parser.catalog.borrow().is_empty());
    }

    #[test]
    fn block_ids_registered_in_catalog() {
        let mut parser = Parser::default();
        let doc = parser.parse("= Test Document\n\n[#my-block]\nSome content with an ID");

        let catalog = doc.catalog();
        assert!(!catalog.is_empty());
        assert!(catalog.contains_id("my-block"));

        let entry = catalog.get_ref("my-block").unwrap();
        assert_eq!(entry.id, "my-block");
        assert_eq!(entry.ref_type, crate::document::RefType::Anchor);
    }

    /// A simple test renderer that modifies special characters differently
    /// from the default HTML renderer.
    #[derive(Debug)]
    struct TestRenderer;

    impl InlineSubstitutionRenderer for TestRenderer {
        fn render_special_character(&self, type_: SpecialCharacter, dest: &mut String) {
            // Custom rendering: wrap special characters in brackets.
            match type_ {
                SpecialCharacter::Lt => dest.push_str("[LT]"),
                SpecialCharacter::Gt => dest.push_str("[GT]"),
                SpecialCharacter::Ampersand => dest.push_str("[AMP]"),
            }
        }

        fn render_quoted_substitition(
            &self,
            _type_: QuoteType,
            _scope: QuoteScope,
            _attrlist: Option<Attrlist<'_>>,
            _id: Option<String>,
            body: &str,
            dest: &mut String,
        ) {
            dest.push_str(body);
        }

        fn render_character_replacement(
            &self,
            _type_: CharacterReplacementType,
            dest: &mut String,
        ) {
            dest.push_str("[CHAR]");
        }

        fn render_line_break(&self, dest: &mut String) {
            dest.push_str("[BR]");
        }

        fn render_image(&self, _params: &ImageRenderParams, dest: &mut String) {
            dest.push_str("[IMAGE]");
        }

        fn image_uri(
            &self,
            target_image_path: &str,
            _parser: &Parser,
            _asset_dir_key: Option<&str>,
        ) -> String {
            target_image_path.to_string()
        }

        fn render_icon(&self, _params: &IconRenderParams, dest: &mut String) {
            dest.push_str("[ICON]");
        }

        fn render_link(&self, _params: &LinkRenderParams, dest: &mut String) {
            dest.push_str("[LINK]");
        }

        fn render_anchor(&self, id: &str, _reftext: Option<String>, dest: &mut String) {
            dest.push_str(&format!("[ANCHOR:{}]", id));
        }

        fn render_xref(&self, params: &crate::parser::XrefRenderParams, dest: &mut String) {
            dest.push_str(&format!("[XREF:{}]", params.target));
        }

        fn render_callout(&self, params: &crate::parser::CalloutRenderParams, dest: &mut String) {
            dest.push_str(&format!("[CALLOUT:{}]", params.number));
        }
    }

    #[test]
    fn with_inline_substitution_renderer() {
        let mut parser = Parser::default().with_inline_substitution_renderer(TestRenderer);

        // Parse a simple document with special characters.
        let doc = parser.parse("Hello & goodbye < world > test");

        // The document should parse successfully.
        assert_eq!(doc.warnings().count(), 0);

        // Get the first block from the document.
        let block = doc.nested_blocks().next().unwrap();

        let Block::Simple(simple_block) = block else {
            panic!("Expected simple block, got: {block:?}");
        };

        // Our custom renderer should show [AMP], [LT], and [GT] instead of HTML
        // entities.
        assert_eq!(
            simple_block.content().rendered(),
            "Hello [AMP] goodbye [LT] world [GT] test"
        );
    }

    mod resolve_show_title {
        use crate::parser::{ModificationContext, Parser};

        fn with(name: &str, set: bool) -> Parser {
            Parser::default().with_intrinsic_attribute_bool(
                name,
                set,
                ModificationContext::Anywhere,
            )
        }

        #[test]
        fn neither_present_uses_default() {
            assert!(Parser::default().resolve_show_title(true));
            assert!(!Parser::default().resolve_show_title(false));
        }

        #[test]
        fn showtitle_takes_precedence_and_decides() {
            // Present and set -> shown; present and unset -> hidden, regardless
            // of the default.
            assert!(with("showtitle", true).resolve_show_title(false));
            assert!(!with("showtitle", false).resolve_show_title(true));
        }

        #[test]
        fn notitle_is_the_complement_when_showtitle_absent() {
            // notitle set -> hidden; notitle unset -> shown.
            assert!(!with("notitle", true).resolve_show_title(true));
            assert!(with("notitle", false).resolve_show_title(false));
        }
    }

    mod refresh_doctype_derived_attr {
        use crate::{document::InterpretedValue, parser::Parser};

        #[test]
        fn tracks_the_active_doctype() {
            let mut parser = Parser::default();

            // The default doctype is `article`, so only its derived attribute is
            // defined (to an empty value).
            assert_eq!(
                parser.attribute_value("backend-html5-doctype-article"),
                InterpretedValue::Value(String::new())
            );
            assert_eq!(
                parser.attribute_value("backend-html5-doctype-book"),
                InterpretedValue::Unset
            );

            // Forcing a new doctype moves the derived attribute with it.
            parser.force_doctype("book");
            assert_eq!(
                parser.attribute_value("backend-html5-doctype-book"),
                InterpretedValue::Value(String::new())
            );
            assert_eq!(
                parser.attribute_value("backend-html5-doctype-article"),
                InterpretedValue::Unset
            );
        }

        #[test]
        fn defines_no_derived_attr_when_doctype_is_not_a_value() {
            let mut parser = Parser::default();

            // The default article derived attribute starts out defined.
            assert_eq!(
                parser.attribute_value("backend-html5-doctype-article"),
                InterpretedValue::Value(String::new())
            );

            // With `doctype` unset (no `Value`), a refresh clears any existing
            // derived attribute and defines none.
            std::sync::Arc::make_mut(&mut parser.attribute_values).remove("doctype");
            parser.refresh_doctype_derived_attr();

            assert_eq!(parser.attribute_value("doctype"), InterpretedValue::Unset);
            assert_eq!(
                parser.attribute_value("backend-html5-doctype-article"),
                InterpretedValue::Unset
            );
        }
    }

    mod docname {
        use crate::Parser;

        #[test]
        fn none_without_primary_file_name() {
            assert_eq!(Parser::default().docname(), None);
        }

        #[test]
        fn strips_directory_and_extension() {
            assert_eq!(
                Parser::default()
                    .with_primary_file_name("mydoc.adoc")
                    .docname()
                    .as_deref(),
                Some("mydoc")
            );
            assert_eq!(
                Parser::default()
                    .with_primary_file_name("docs/guide/mydoc.adoc")
                    .docname()
                    .as_deref(),
                Some("mydoc")
            );
            // A Windows-style separator is handled too, since the primary file
            // name may be supplied on either platform.
            assert_eq!(
                Parser::default()
                    .with_primary_file_name(r"docs\guide\mydoc.adoc")
                    .docname()
                    .as_deref(),
                Some("mydoc")
            );
        }

        #[test]
        fn keeps_name_with_no_extension() {
            assert_eq!(
                Parser::default()
                    .with_primary_file_name("README")
                    .docname()
                    .as_deref(),
                Some("README")
            );
        }

        #[test]
        fn none_when_path_has_no_file_component() {
            // A primary file name that ends in a separator has an empty base
            // name, which yields no document name.
            assert_eq!(
                Parser::default()
                    .with_primary_file_name("docs/guide/")
                    .docname(),
                None
            );
        }

        #[test]
        fn leading_dot_name_is_kept_whole() {
            // A leading-dot name (e.g. `.adoc`) is treated as a dotfile with no
            // extension and kept whole, matching Ruby's
            // `File.basename(".adoc", ".*")`.
            assert_eq!(
                Parser::default()
                    .with_primary_file_name(".adoc")
                    .docname()
                    .as_deref(),
                Some(".adoc")
            );
        }
    }

    mod counter {
        use super::super::next_counter_value;
        use crate::{document::InterpretedValue, tests::prelude::*};

        #[test]
        fn next_counter_value_integer() {
            assert_eq!(next_counter_value("1"), "2");
            assert_eq!(next_counter_value("9"), "10");
            assert_eq!(next_counter_value("0"), "1");
            assert_eq!(next_counter_value("-1"), "0");
        }

        #[test]
        fn next_counter_value_non_canonical_integer_is_advanced_as_a_string() {
            // A leading zero (or sign) does not round-trip through integer
            // parsing, so it is advanced like a string instead.
            assert_eq!(next_counter_value("07"), "08");
            assert_eq!(next_counter_value("+5"), "+6");
            // A leading-zero value still carries digit-to-digit like a string.
            assert_eq!(next_counter_value("09"), "10");
            assert_eq!(next_counter_value("099"), "100");
        }

        #[test]
        fn next_counter_value_saturates_at_i64_max() {
            // A counter pinned at `i64::MAX` stays there rather than panicking
            // (debug) or wrapping (release).
            let max = i64::MAX.to_string();
            assert_eq!(next_counter_value(&max), max);
        }

        #[test]
        fn next_counter_value_characters() {
            assert_eq!(next_counter_value("a"), "b");
            assert_eq!(next_counter_value("A"), "B");
            assert_eq!(next_counter_value("z"), "aa");
            assert_eq!(next_counter_value("Z"), "AA");
            assert_eq!(next_counter_value("az"), "ba");
            assert_eq!(next_counter_value("zz"), "aaa");
            assert_eq!(next_counter_value("Zz"), "AAa");
        }

        #[test]
        fn next_counter_value_trailing_non_alphanumeric() {
            // The right-most alphanumeric is incremented; trailing punctuation is
            // left in place.
            assert_eq!(next_counter_value("a)"), "b)");
        }

        #[test]
        fn next_counter_value_no_alphanumeric() {
            // With nothing alphanumeric to carry, the final code point advances.
            assert_eq!(next_counter_value("{"), "|");
        }

        #[test]
        fn counter_defaults_to_one() {
            let p = Parser::default();
            assert_eq!(p.counter("x", None), "1");
            assert_eq!(p.counter("x", None), "2");
            assert_eq!(
                p.attribute_value("x"),
                InterpretedValue::Value("2".to_string())
            );
            assert!(p.has_attribute("x"));
            assert!(p.is_attribute_set("x"));
        }

        #[test]
        fn counter_seed_used_only_while_unset() {
            let p = Parser::default();
            assert_eq!(p.counter("c", Some("A")), "A");
            // Once set, a later seed is ignored.
            assert_eq!(p.counter("c", Some("Q")), "B");
        }

        #[test]
        fn counter_empty_seed_falls_back_to_one() {
            let p = Parser::default();
            assert_eq!(p.counter("c", Some("")), "1");
        }
    }
}