tablo-core 0.2.0

//! The crate's layers: a module names its own layer and the ones below it, never one above.
//!
//! The check reads the sources: every `crate::` path, every `super::` path that leaves its
//! top-level module, and every root re-export they go through. Tests and their fixtures are
//! exempt, since a test may drive any layer.

use std::{
    collections::HashMap,
    fs,
    path::{Path, PathBuf},
};

/// The top-level modules of each layer, lowest first.
const LAYERS: &[(&str, &[&str])] = &[
    (
        "foundations",
        &[
            "csrf",
            "db",
            "declaration",
            "error",
            "lens",
            "naming",
            "query_term",
            "toasty_compat",
            "topcoat_compat",
        ],
    ),
    (
        "the declaration model",
        &["form", "navigation", "policy", "schema", "table", "tenancy"],
    ),
    ("resources", &["resource"]),
    (
        "serving",
        &["auth", "notification", "page", "panel", "upload"],
    ),
];

#[test]
fn every_module_reaches_only_its_own_layer_and_the_ones_below() {
    let src = Path::new(env!("CARGO_MANIFEST_DIR")).join("src");
    let lib = strip(&fs::read_to_string(src.join("lib.rs")).expect("read lib.rs"));
    for module in declared_modules(&lib) {
        assert!(
            layer(&module).is_some(),
            "`{module}` is in no layer: add it to `LAYERS`"
        );
    }
    let exports = root_exports(&lib);
    let mut reached_up = Vec::new();
    for file in sources(&src) {
        let relative = file.strip_prefix(&src).expect("under src");
        let segments = module_path(relative);
        let from = &segments[0];
        let from_layer = layer(from).expect("every module is in a layer");
        let text = strip(&fs::read_to_string(&file).expect("read a source"));
        for target in reached_modules(&text, &segments) {
            let target = exports.get(&target).cloned().unwrap_or(target);
            if layer(&target).is_some_and(|to| to > from_layer) {
                reached_up.push(format!(
                    "{} reaches `{target}` in {}",
                    relative.display(),
                    LAYERS[layer(&target).expect("checked")].0
                ));
            }
        }
    }
    reached_up.sort();
    reached_up.dedup();
    assert!(
        reached_up.is_empty(),
        "a module reaches a layer above its own:\n{}",
        reached_up.join("\n")
    );
}

fn layer(module: &str) -> Option<usize> {
    LAYERS
        .iter()
        .position(|(_, modules)| modules.contains(&module))
}

/// The source files the check reads: everything under `src` but the crate root, tests and test
/// fixtures.
fn sources(dir: &Path) -> Vec<PathBuf> {
    let root = dir.ends_with("src");
    let mut files = Vec::new();
    for entry in fs::read_dir(dir).expect("read a source directory") {
        let path = entry.expect("a directory entry").path();
        let name = path
            .file_name()
            .and_then(|name| name.to_str())
            .unwrap_or("");
        if path.is_dir() {
            if name != "tests" {
                files.extend(sources(&path));
            }
        } else if name.ends_with(".rs")
            && !matches!(name, "tests.rs" | "test_support.rs")
            && !(root && name == "lib.rs")
        {
            files.push(path);
        }
    }
    files
}

/// `panel/forms/submit.rs` → `[panel, forms, submit]`; a `mod.rs` names its directory.
fn module_path(relative: &Path) -> Vec<String> {
    let mut segments: Vec<String> = relative
        .iter()
        .map(|segment| {
            segment
                .to_string_lossy()
                .trim_end_matches(".rs")
                .to_string()
        })
        .collect();
    if segments.last().is_some_and(|last| last == "mod") {
        segments.pop();
    }
    segments
}

/// The top-level modules `text`, in the module at `segments`, names.
fn reached_modules(text: &str, segments: &[String]) -> Vec<String> {
    let mut reached = Vec::new();
    let mut rest = text;
    while let Some(at) = rest.find("crate::") {
        let preceded = rest[..at]
            .chars()
            .next_back()
            .is_some_and(|c| c.is_alphanumeric() || c == '_' || c == ':');
        rest = &rest[at + "crate::".len()..];
        if !preceded {
            reached.extend(first_segments(rest));
        }
    }
    // `super::` that climbs out of the top-level module lands at the crate root.
    let mut rest = text;
    while let Some(at) = rest.find("super::") {
        let preceded = rest[..at]
            .chars()
            .next_back()
            .is_some_and(|c| c.is_alphanumeric() || c == '_' || c == ':');
        rest = &rest[at..];
        let mut climbs = 0;
        while let Some(after) = rest.strip_prefix("super::") {
            climbs += 1;
            rest = after;
        }
        if !preceded && climbs >= segments.len() {
            reached.extend(first_segments(rest));
        }
    }
    reached
}

/// The first segment of the path at the start of `rest`, or of every path in a `{..}` group.
fn first_segments(rest: &str) -> Vec<String> {
    match rest.strip_prefix('{') {
        Some(group) => top_level_items(&group[..group_end(group)])
            .iter()
            .filter_map(|item| identifier(item))
            .collect(),
        None => identifier(rest).into_iter().collect(),
    }
}

fn identifier(text: &str) -> Option<String> {
    let text = text.trim_start();
    let end = text
        .find(|c: char| !(c.is_alphanumeric() || c == '_'))
        .unwrap_or(text.len());
    (end > 0).then(|| text[..end].to_string())
}

/// The index of the `}` that closes a group whose `{` precedes `group`.
fn group_end(group: &str) -> usize {
    let mut depth = 1;
    for (index, c) in group.char_indices() {
        match c {
            '{' => depth += 1,
            '}' => {
                depth -= 1;
                if depth == 0 {
                    return index;
                }
            }
            _ => {}
        }
    }
    group.len()
}

/// A `{..}` group's comma-separated items, nested groups kept whole.
fn top_level_items(group: &str) -> Vec<&str> {
    let mut items = Vec::new();
    let (mut depth, mut start) = (0, 0);
    for (index, c) in group.char_indices() {
        match c {
            '{' => depth += 1,
            '}' => depth -= 1,
            ',' if depth == 0 => {
                items.push(group[start..index].trim());
                start = index + 1;
            }
            _ => {}
        }
    }
    items.push(group[start..].trim());
    items.retain(|item| !item.is_empty());
    items
}

/// The top-level modules the crate root declares, test-only ones aside.
fn declared_modules(lib: &str) -> Vec<String> {
    let mut modules = Vec::new();
    let mut test_only = false;
    for line in lib.lines().map(str::trim) {
        if line == "#[cfg(test)]" {
            test_only = true;
            continue;
        }
        let declared = line
            .strip_prefix("pub mod ")
            .or_else(|| line.strip_prefix("mod "))
            .and_then(|rest| rest.strip_suffix(';'));
        if let Some(module) = declared
            && !test_only
        {
            modules.push(module.to_string());
        }
        test_only = false;
    }
    modules
}

/// Each name the crate root re-exports, mapped to the module it comes from.
fn root_exports(lib: &str) -> HashMap<String, String> {
    let mut exports = HashMap::new();
    let mut rest = lib;
    while let Some(at) = rest.find("\npub use ") {
        rest = &rest[at + "\npub use ".len()..];
        let statement = &rest[..rest.find(';').unwrap_or(rest.len())];
        let Some(module) = identifier(statement) else {
            continue;
        };
        for leaf in leaves(statement) {
            exports.insert(leaf, module.clone());
        }
    }
    exports
}

/// The last segment of every path a `use` tree names.
fn leaves(tree: &str) -> Vec<String> {
    let mut leaves = Vec::new();
    let mut word = String::new();
    let chars: Vec<char> = tree.chars().collect();
    for (index, &c) in chars.iter().enumerate() {
        if c.is_alphanumeric() || c == '_' {
            word.push(c);
            continue;
        }
        if !word.is_empty() && !(c == ':' && chars.get(index + 1) == Some(&':')) {
            leaves.push(std::mem::take(&mut word));
        }
        word.clear();
    }
    if !word.is_empty() {
        leaves.push(word);
    }
    leaves
}

/// `source` without its comments and the contents of its string and character literals.
fn strip(source: &str) -> String {
    let mut out = String::with_capacity(source.len());
    let mut chars = source.chars().peekable();
    while let Some(c) = chars.next() {
        match c {
            '/' if chars.peek() == Some(&'/') => {
                for c in chars.by_ref() {
                    if c == '\n' {
                        out.push('\n');
                        break;
                    }
                }
            }
            '/' if chars.peek() == Some(&'*') => {
                chars.next();
                let mut previous = ' ';
                for c in chars.by_ref() {
                    if previous == '*' && c == '/' {
                        break;
                    }
                    previous = c;
                }
            }
            '\'' => {
                // A character literal is skipped; a lifetime's quote is kept.
                let mut ahead = chars.clone();
                match (ahead.next(), ahead.next()) {
                    (Some('\\'), _) => {
                        for c in chars.by_ref() {
                            if c == '\'' {
                                break;
                            }
                        }
                    }
                    (Some(_), Some('\'')) => {
                        chars.next();
                        chars.next();
                    }
                    _ => out.push(c),
                }
            }
            '"' => {
                out.push('"');
                while let Some(c) = chars.next() {
                    match c {
                        '\\' => {
                            chars.next();
                        }
                        '"' => break,
                        _ => {}
                    }
                }
                out.push('"');
            }
            _ => out.push(c),
        }
    }
    out
}