html-conform 0.1.1

HTML5 conformance checking as a pure Rust dependency (vnu-comparable, no JVM runtime).
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313

//! Co-constraint (Schematron-style) assertion checking — ARIA combinations,
//! form-label requirements, table semantics, obsolete elements — behind the
//! [`SchematronEngine`] trait, so this module never talks to a concrete
//! Schematron backend directly outside [`RuleSetEngine`]'s single
//! implementation of it (`CLAUDE.md`, "Feste Regeln").
//!
//! Rule files (`rules/*.sch`) are the only place for this domain's fachliche
//! Logik — declarative XPath, no Rust co-constraint code (`CLAUDE.md`). This
//! module only loads, runs, and maps their results; see `rules/README.md`
//! for the rule-authoring contract (notably: named element tests need the
//! `h:` namespace prefix against this crate's XHTML-namespaced infoset).
//!
//! [`findings`]/[`RuleSetEngine`] are wired into
//! [`crate::check`]/[`crate::check_with_options`], combined there with
//! schema (RELAX NG) and parser findings into one [`crate::CheckReport`].

use std::error::Error;
use std::fmt;
use std::sync::LazyLock;

use crate::finding::{Finding, Severity};
use crate::infoset::NormalizedHtmlDocument;

/// A structured Schematron assertion failure — [`SchematronEngine`]'s only
/// output shape, engine-agnostic (no `schematron_engine::Report` or other
/// backend type leaks through this module's public surface).
#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) struct AssertionFailure {
    /// The fired check's stable id (`assert`/`report`'s `@id` in the rule
    /// file). Every rule in `rules/*.sch` must have one — a fired check
    /// with no id is a rule-authoring bug, surfaced as an [`EngineError`]
    /// rather than silently producing an empty/placeholder id (see
    /// [`RuleSetEngine::check`]).
    pub(crate) rule_id: String,
    /// Derived from the rule's `@role` attribute — see
    /// [`severity_from_role`] for the convention this crate defines (ISO
    /// Schematron's `role` is free text with no standardized severity
    /// meaning).
    pub(crate) severity: Severity,
    pub(crate) message: String,
    /// The fired check's context node's position, if any (`None` for a
    /// node html5-parser itself synthesizes — an implied `<html>`/
    /// `<head>`/`<body>`, say — see `src/infoset.rs`'s `normalize` doc
    /// comment). Sourced from `schematron_engine::Report::node`, not
    /// computed here — see `RuleSetEngine::check`.
    pub(crate) location: Option<crate::finding::SourceLocation>,
}

/// An assertion-engine evaluation failure — a bug in the rule set or its
/// loading (a malformed `test`/`context` expression, a missing `@id`), not
/// a property of the checked document. Distinct from a `Vec<AssertionFailure>`
/// being empty (which just means no rule fired).
#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) struct EngineError(String);

impl fmt::Display for EngineError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(formatter, "assertion engine error: {}", self.0)
    }
}

impl Error for EngineError {}

/// Abstraction over a Schematron rule-evaluation backend. See this module's
/// doc comment for why `assertions.rs` is required to go through this trait
/// rather than a concrete engine type directly.
pub(crate) trait SchematronEngine {
    /// Runs this engine's rule set against `document`, in rule-file/pattern/
    /// rule order. `Err` only for a genuine evaluation failure (the rule
    /// set itself is broken), never for "no rule fired" (that's `Ok(vec![])`).
    fn check(
        &self,
        document: &NormalizedHtmlDocument,
    ) -> Result<Vec<AssertionFailure>, EngineError>;
}

/// This crate's own convention for turning ISO Schematron's free-text
/// `role` attribute into a [`Severity`] — ISO Schematron itself assigns no
/// standardized meaning to `role`. `"warning"`/`"info"` (case-sensitive,
/// matching this crate's own `rules/*.sch` authoring convention) map to the
/// matching [`Severity`]; anything else (including no `role` at all, or
/// literally `"error"`) defaults to [`Severity::Error`] — a conformance
/// checker's assertions are errors unless a rule explicitly opts into a
/// softer severity.
fn severity_from_role(role: Option<&str>) -> Severity {
    match role {
        Some("warning") => Severity::Warning,
        Some("info") => Severity::Info,
        _ => Severity::Error,
    }
}

/// The rule files this crate's assertion layer embeds, in the fixed order
/// they're evaluated and findings are reported in. Each is a complete,
/// independently valid ISO Schematron `<schema>` document — see
/// `rules/README.md`.
const RULE_FILES: &[(&str, &str)] = &[
    ("aria.sch", include_str!("../rules/aria.sch")),
    ("tables.sch", include_str!("../rules/tables.sch")),
    (
        "obsolete-elements.sch",
        include_str!("../rules/obsolete-elements.sch"),
    ),
    ("ids.sch", include_str!("../rules/ids.sch")),
    ("microdata.sch", include_str!("../rules/microdata.sch")),
    ("headings.sch", include_str!("../rules/headings.sch")),
    ("roles.sch", include_str!("../rules/roles.sch")),
    ("elements.sch", include_str!("../rules/elements.sch")),
    (
        "aria-constraints.sch",
        include_str!("../rules/aria-constraints.sch"),
    ),
    (
        "aria-html-restrictions.sch",
        include_str!("../rules/aria-html-restrictions.sch"),
    ),
    ("attributes.sch", include_str!("../rules/attributes.sch")),
];

/// Parses every embedded [`RULE_FILES`] entry once, in order, failing loudly
/// (rather than skipping) if any of them doesn't parse — a broken rule file
/// is a build-time bug, not a per-document condition.
fn parse_rule_files() -> Result<Vec<schematron_engine::Schema>, EngineError> {
    RULE_FILES
        .iter()
        .map(|(name, xml)| {
            schematron_engine::parse(xml)
                .map_err(|error| EngineError(format!("rules/{name}: {error}")))
        })
        .collect()
}

/// Compiled once (see `src/schema.rs`'s `HTML5_SCHEMA` for the same
/// pattern) and cached for the process lifetime.
static RULE_SCHEMAS: LazyLock<Result<Vec<schematron_engine::Schema>, EngineError>> =
    LazyLock::new(parse_rule_files);

/// The [`SchematronEngine`] implementation backed by `schematron-engine`
/// and this crate's embedded [`RULE_FILES`]. The only place in this crate
/// that names `schematron_engine` types outside this module's own
/// [`SchematronEngine`]-trait boundary.
pub(crate) struct RuleSetEngine;

impl SchematronEngine for RuleSetEngine {
    fn check(
        &self,
        document: &NormalizedHtmlDocument,
    ) -> Result<Vec<AssertionFailure>, EngineError> {
        let schemas = RULE_SCHEMAS.as_ref().map_err(Clone::clone)?;

        let mut failures = Vec::new();
        for schema in schemas {
            let reports = schematron_engine::evaluate(schema, document)
                .map_err(|error| EngineError(error.to_string()))?;
            for report in reports {
                let Some(rule_id) = report.check_id else {
                    return Err(EngineError(format!(
                        "fired check in pattern {:?} has no @id — every rules/*.sch assert/report must declare one",
                        report.pattern_id
                    )));
                };
                failures.push(AssertionFailure {
                    rule_id,
                    severity: severity_from_role(report.role.as_deref()),
                    message: report.message,
                    location: report.node.position().copied(),
                });
            }
        }
        Ok(failures)
    }
}

/// Maps [`AssertionFailure`]s onto this crate's public [`Finding`] model.
/// `rule_id` is prefixed with `assertion.` (plan/06-assertions-engine.md)
/// to namespace it against the `parser.*`/future `schema.*` layers'
/// findings — e.g. `assertion.aria.hidden-not-focusable`.
pub(crate) fn findings(failures: &[AssertionFailure]) -> Vec<Finding> {
    failures
        .iter()
        .map(|failure| Finding {
            rule_id: format!("assertion.{}", failure.rule_id),
            severity: failure.severity,
            message: failure.message.clone(),
            location: failure.location,
        })
        .collect()
}

#[cfg(test)]
mod tests {
    use super::{AssertionFailure, EngineError, RuleSetEngine, SchematronEngine, findings};
    use crate::finding::Severity;
    use crate::infoset::normalize;
    use crate::parse::parse;

    fn check_html(html: &str) -> Vec<AssertionFailure> {
        let parsed = parse(html);
        let document = normalize(parsed.document(), parsed.source());
        RuleSetEngine
            .check(&document)
            .expect("rule set should evaluate without an engine error")
    }

    #[test]
    fn all_embedded_rule_files_parse() {
        // Mirrors src/schema.rs's `embedded_html5_schema_compiles` — a
        // broken rules/*.sch file should fail a test, not surface only at
        // first real use.
        super::parse_rule_files().expect("every embedded rule file should parse");
    }

    #[test]
    fn aria_hidden_with_tabindex_fires() {
        let failures = check_html(r#"<div aria-hidden="true" tabindex="0">x</div>"#);
        assert_eq!(failures.len(), 1);
        assert_eq!(failures[0].rule_id, "aria.hidden-not-focusable");
        assert_eq!(failures[0].severity, Severity::Error);
    }

    #[test]
    fn aria_hidden_without_tabindex_is_clean() {
        let failures = check_html(r#"<div aria-hidden="true">x</div>"#);
        assert!(failures.is_empty());
    }

    #[test]
    fn th_scope_enum_valid_and_invalid() {
        assert!(check_html(r#"<table><tr><th scope="col">A</th></tr></table>"#).is_empty());
        let failures = check_html(r#"<table><tr><th scope="column">A</th></tr></table>"#);
        assert_eq!(failures.len(), 1);
        assert_eq!(failures[0].rule_id, "tables.th-scope-enum");
    }

    #[test]
    fn obsolete_elements_fire_and_ordinary_elements_dont() {
        let failures = check_html("<font>x</font><center>y</center>");
        assert_eq!(failures.len(), 2);
        assert!(
            failures
                .iter()
                .all(|f| f.rule_id == "obsolete-elements.deprecated")
        );

        assert!(check_html("<p>ordinary</p>").is_empty());
    }

    #[test]
    fn multiple_rule_files_fire_independently_in_one_document() {
        let failures = check_html(
            r#"<div aria-hidden="true" tabindex="0">x</div><table><tr><th scope="column">A</th></tr></table><font>x</font>"#,
        );
        let rule_ids: Vec<&str> = failures.iter().map(|f| f.rule_id.as_str()).collect();
        assert!(rule_ids.contains(&"aria.hidden-not-focusable"));
        assert!(rule_ids.contains(&"tables.th-scope-enum"));
        assert!(rule_ids.contains(&"obsolete-elements.deprecated"));
    }

    #[test]
    fn findings_prefixes_rule_id_and_carries_severity_and_message() {
        let failures = vec![AssertionFailure {
            rule_id: "aria.hidden-not-focusable".to_owned(),
            severity: Severity::Error,
            message: "boom".to_owned(),
            location: None,
        }];
        let mapped = findings(&failures);
        assert_eq!(mapped.len(), 1);
        assert_eq!(mapped[0].rule_id, "assertion.aria.hidden-not-focusable");
        assert_eq!(mapped[0].severity, Severity::Error);
        assert_eq!(mapped[0].message, "boom");
        assert_eq!(mapped[0].location, None);
    }

    /// Demonstrates the `SchematronEngine` trait's whole point: a caller
    /// (or a future test elsewhere in this crate) can swap in any
    /// implementation, not just `RuleSetEngine`/`schematron-engine` — this
    /// mock never touches `schematron_engine` or `rules/*.sch` at all.
    struct MockEngine {
        result: Result<Vec<AssertionFailure>, EngineError>,
    }

    impl SchematronEngine for MockEngine {
        fn check(
            &self,
            _document: &crate::infoset::NormalizedHtmlDocument,
        ) -> Result<Vec<AssertionFailure>, EngineError> {
            self.result.clone()
        }
    }

    #[test]
    fn schematron_engine_trait_is_swappable_for_a_mock_implementation() {
        let parsed = parse("<p>irrelevant — the mock ignores the document</p>");
        let document = normalize(parsed.document(), parsed.source());

        let canned = vec![AssertionFailure {
            rule_id: "mock.rule".to_owned(),
            severity: Severity::Warning,
            message: "mock failure".to_owned(),
            location: None,
        }];
        let engine = MockEngine {
            result: Ok(canned.clone()),
        };
        assert_eq!(engine.check(&document).unwrap(), canned);

        let failing_engine = MockEngine {
            result: Err(EngineError("mock engine error".to_owned())),
        };
        assert!(failing_engine.check(&document).is_err());
    }
}