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
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
use std::cmp;

use rustc_data_structures::fx::FxIndexMap;
use rustc_data_structures::sorted_map::SortedMap;
use rustc_errors::{Diag, DiagMessage, MultiSpan};
use rustc_hir::{HirId, ItemLocalId};
use rustc_session::lint::{
    builtin::{self, FORBIDDEN_LINT_GROUPS},
    FutureIncompatibilityReason, Level, Lint, LintId,
};
use rustc_session::Session;
use rustc_span::hygiene::{ExpnKind, MacroKind};
use rustc_span::{symbol, DesugaringKind, Span, Symbol, DUMMY_SP};

use crate::ty::TyCtxt;

/// How a lint level was set.
#[derive(Clone, Copy, PartialEq, Eq, HashStable, Debug)]
pub enum LintLevelSource {
    /// Lint is at the default level as declared in rustc.
    Default,

    /// Lint level was set by an attribute.
    Node {
        name: Symbol,
        span: Span,
        /// RFC 2383 reason
        reason: Option<Symbol>,
    },

    /// Lint level was set by a command-line flag.
    /// The provided `Level` is the level specified on the command line.
    /// (The actual level may be lower due to `--cap-lints`.)
    CommandLine(Symbol, Level),
}

impl LintLevelSource {
    pub fn name(&self) -> Symbol {
        match *self {
            LintLevelSource::Default => symbol::kw::Default,
            LintLevelSource::Node { name, .. } => name,
            LintLevelSource::CommandLine(name, _) => name,
        }
    }

    pub fn span(&self) -> Span {
        match *self {
            LintLevelSource::Default => DUMMY_SP,
            LintLevelSource::Node { span, .. } => span,
            LintLevelSource::CommandLine(_, _) => DUMMY_SP,
        }
    }
}

/// A tuple of a lint level and its source.
pub type LevelAndSource = (Level, LintLevelSource);

/// Return type for the `shallow_lint_levels_on` query.
///
/// This map represents the set of allowed lints and allowance levels given
/// by the attributes for *a single HirId*.
#[derive(Default, Debug, HashStable)]
pub struct ShallowLintLevelMap {
    pub specs: SortedMap<ItemLocalId, FxIndexMap<LintId, LevelAndSource>>,
}

/// From an initial level and source, verify the effect of special annotations:
/// `warnings` lint level and lint caps.
///
/// The return of this function is suitable for diagnostics.
pub fn reveal_actual_level(
    level: Option<Level>,
    src: &mut LintLevelSource,
    sess: &Session,
    lint: LintId,
    probe_for_lint_level: impl FnOnce(LintId) -> (Option<Level>, LintLevelSource),
) -> Level {
    // If `level` is none then we actually assume the default level for this lint.
    let mut level = level.unwrap_or_else(|| lint.lint.default_level(sess.edition()));

    // If we're about to issue a warning, check at the last minute for any
    // directives against the warnings "lint". If, for example, there's an
    // `allow(warnings)` in scope then we want to respect that instead.
    //
    // We exempt `FORBIDDEN_LINT_GROUPS` from this because it specifically
    // triggers in cases (like #80988) where you have `forbid(warnings)`,
    // and so if we turned that into an error, it'd defeat the purpose of the
    // future compatibility warning.
    if level == Level::Warn && lint != LintId::of(FORBIDDEN_LINT_GROUPS) {
        let (warnings_level, warnings_src) = probe_for_lint_level(LintId::of(builtin::WARNINGS));
        if let Some(configured_warning_level) = warnings_level {
            if configured_warning_level != Level::Warn {
                level = configured_warning_level;
                *src = warnings_src;
            }
        }
    }

    // Ensure that we never exceed the `--cap-lints` argument unless the source is a --force-warn
    level = if let LintLevelSource::CommandLine(_, Level::ForceWarn(_)) = src {
        level
    } else {
        cmp::min(level, sess.opts.lint_cap.unwrap_or(Level::Forbid))
    };

    if let Some(driver_level) = sess.driver_lint_caps.get(&lint) {
        // Ensure that we never exceed driver level.
        level = cmp::min(*driver_level, level);
    }

    level
}

impl ShallowLintLevelMap {
    /// Perform a deep probe in the HIR tree looking for the actual level for the lint.
    /// This lint level is not usable for diagnostics, it needs to be corrected by
    /// `reveal_actual_level` beforehand.
    #[instrument(level = "trace", skip(self, tcx), ret)]
    fn probe_for_lint_level(
        &self,
        tcx: TyCtxt<'_>,
        id: LintId,
        start: HirId,
    ) -> (Option<Level>, LintLevelSource) {
        if let Some(map) = self.specs.get(&start.local_id)
            && let Some(&(level, src)) = map.get(&id)
        {
            return (Some(level), src);
        }

        let mut owner = start.owner;
        let mut specs = &self.specs;

        for parent in tcx.hir().parent_id_iter(start) {
            if parent.owner != owner {
                owner = parent.owner;
                specs = &tcx.shallow_lint_levels_on(owner).specs;
            }
            if let Some(map) = specs.get(&parent.local_id)
                && let Some(&(level, src)) = map.get(&id)
            {
                return (Some(level), src);
            }
        }

        (None, LintLevelSource::Default)
    }

    /// Fetch and return the user-visible lint level for the given lint at the given HirId.
    #[instrument(level = "trace", skip(self, tcx), ret)]
    pub fn lint_level_id_at_node(
        &self,
        tcx: TyCtxt<'_>,
        lint: LintId,
        cur: HirId,
    ) -> (Level, LintLevelSource) {
        let (level, mut src) = self.probe_for_lint_level(tcx, lint, cur);
        let level = reveal_actual_level(level, &mut src, tcx.sess, lint, |lint| {
            self.probe_for_lint_level(tcx, lint, cur)
        });
        (level, src)
    }
}

impl TyCtxt<'_> {
    /// Fetch and return the user-visible lint level for the given lint at the given HirId.
    pub fn lint_level_at_node(self, lint: &'static Lint, id: HirId) -> (Level, LintLevelSource) {
        self.shallow_lint_levels_on(id.owner).lint_level_id_at_node(self, LintId::of(lint), id)
    }
}

/// This struct represents a lint expectation and holds all required information
/// to emit the `unfulfilled_lint_expectations` lint if it is unfulfilled after
/// the `LateLintPass` has completed.
#[derive(Clone, Debug, HashStable)]
pub struct LintExpectation {
    /// The reason for this expectation that can optionally be added as part of
    /// the attribute. It will be displayed as part of the lint message.
    pub reason: Option<Symbol>,
    /// The [`Span`] of the attribute that this expectation originated from.
    pub emission_span: Span,
    /// Lint messages for the `unfulfilled_lint_expectations` lint will be
    /// adjusted to include an additional note. Therefore, we have to track if
    /// the expectation is for the lint.
    pub is_unfulfilled_lint_expectations: bool,
    /// This will hold the name of the tool that this lint belongs to. For
    /// the lint `clippy::some_lint` the tool would be `clippy`, the same
    /// goes for `rustdoc`. This will be `None` for rustc lints
    pub lint_tool: Option<Symbol>,
}

impl LintExpectation {
    pub fn new(
        reason: Option<Symbol>,
        emission_span: Span,
        is_unfulfilled_lint_expectations: bool,
        lint_tool: Option<Symbol>,
    ) -> Self {
        Self { reason, emission_span, is_unfulfilled_lint_expectations, lint_tool }
    }
}

pub fn explain_lint_level_source(
    lint: &'static Lint,
    level: Level,
    src: LintLevelSource,
    err: &mut Diag<'_, ()>,
) {
    let name = lint.name_lower();
    if let Level::Allow = level {
        // Do not point at `#[allow(compat_lint)]` as the reason for a compatibility lint
        // triggering. (#121009)
        return;
    }
    match src {
        LintLevelSource::Default => {
            err.note_once(format!("`#[{}({})]` on by default", level.as_str(), name));
        }
        LintLevelSource::CommandLine(lint_flag_val, orig_level) => {
            let flag = orig_level.to_cmd_flag();
            let hyphen_case_lint_name = name.replace('_', "-");
            if lint_flag_val.as_str() == name {
                err.note_once(format!(
                    "requested on the command line with `{flag} {hyphen_case_lint_name}`"
                ));
            } else {
                let hyphen_case_flag_val = lint_flag_val.as_str().replace('_', "-");
                err.note_once(format!(
                    "`{flag} {hyphen_case_lint_name}` implied by `{flag} {hyphen_case_flag_val}`"
                ));
                err.help_once(format!(
                    "to override `{flag} {hyphen_case_flag_val}` add `#[allow({name})]`"
                ));
            }
        }
        LintLevelSource::Node { name: lint_attr_name, span, reason, .. } => {
            if let Some(rationale) = reason {
                err.note(rationale.to_string());
            }
            err.span_note_once(span, "the lint level is defined here");
            if lint_attr_name.as_str() != name {
                let level_str = level.as_str();
                err.note_once(format!(
                    "`#[{level_str}({name})]` implied by `#[{level_str}({lint_attr_name})]`"
                ));
            }
        }
    }
}

/// The innermost function for emitting lints.
///
/// If you are looking to implement a lint, look for higher level functions,
/// for example:
/// - [`TyCtxt::emit_node_span_lint`]
/// - [`TyCtxt::node_span_lint`]
/// - [`TyCtxt::emit_node_lint`]
/// - [`TyCtxt::node_lint`]
/// - `LintContext::opt_span_lint`
///
/// ## `decorate`
///
/// It is not intended to call `emit`/`cancel` on the `Diag` passed in the `decorate` callback.
#[track_caller]
pub fn lint_level(
    sess: &Session,
    lint: &'static Lint,
    level: Level,
    src: LintLevelSource,
    span: Option<MultiSpan>,
    msg: impl Into<DiagMessage>,
    decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
) {
    // Avoid codegen bloat from monomorphization by immediately doing dyn dispatch of `decorate` to
    // the "real" work.
    #[track_caller]
    fn lint_level_impl(
        sess: &Session,
        lint: &'static Lint,
        level: Level,
        src: LintLevelSource,
        span: Option<MultiSpan>,
        msg: impl Into<DiagMessage>,
        decorate: Box<dyn '_ + for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>)>,
    ) {
        // Check for future incompatibility lints and issue a stronger warning.
        let future_incompatible = lint.future_incompatible;

        let has_future_breakage = future_incompatible.map_or(
            // Default allow lints trigger too often for testing.
            sess.opts.unstable_opts.future_incompat_test && lint.default_level != Level::Allow,
            |incompat| {
                matches!(
                    incompat.reason,
                    FutureIncompatibilityReason::FutureReleaseErrorReportInDeps
                )
            },
        );

        // Convert lint level to error level.
        let err_level = match level {
            Level::Allow => {
                if has_future_breakage {
                    rustc_errors::Level::Allow
                } else {
                    return;
                }
            }
            Level::Expect(expect_id) => {
                // This case is special as we actually allow the lint itself in this context, but
                // we can't return early like in the case for `Level::Allow` because we still
                // need the lint diagnostic to be emitted to `rustc_error::DiagCtxtInner`.
                //
                // We can also not mark the lint expectation as fulfilled here right away, as it
                // can still be cancelled in the decorate function. All of this means that we simply
                // create a `Diag` and continue as we would for warnings.
                rustc_errors::Level::Expect(expect_id)
            }
            Level::ForceWarn(Some(expect_id)) => rustc_errors::Level::ForceWarning(Some(expect_id)),
            Level::ForceWarn(None) => rustc_errors::Level::ForceWarning(None),
            Level::Warn => rustc_errors::Level::Warning,
            Level::Deny | Level::Forbid => rustc_errors::Level::Error,
        };
        let mut err = Diag::new(sess.dcx(), err_level, "");
        if let Some(span) = span {
            err.span(span);
        }

        // If this code originates in a foreign macro, aka something that this crate
        // did not itself author, then it's likely that there's nothing this crate
        // can do about it. We probably want to skip the lint entirely.
        if err.span.primary_spans().iter().any(|s| in_external_macro(sess, *s)) {
            // Any suggestions made here are likely to be incorrect, so anything we
            // emit shouldn't be automatically fixed by rustfix.
            err.disable_suggestions();

            // If this is a future incompatible that is not an edition fixing lint
            // it'll become a hard error, so we have to emit *something*. Also,
            // if this lint occurs in the expansion of a macro from an external crate,
            // allow individual lints to opt-out from being reported.
            let incompatible = future_incompatible.is_some_and(|f| f.reason.edition().is_none());

            if !incompatible && !lint.report_in_external_macro {
                err.cancel();

                // Don't continue further, since we don't want to have
                // `diag_span_note_once` called for a diagnostic that isn't emitted.
                return;
            }
        }

        // Delay evaluating and setting the primary message until after we've
        // suppressed the lint due to macros.
        err.primary_message(msg);

        err.is_lint(lint.name_lower(), has_future_breakage);

        // Lint diagnostics that are covered by the expect level will not be emitted outside
        // the compiler. It is therefore not necessary to add any information for the user.
        // This will therefore directly call the decorate function which will in turn emit
        // the diagnostic.
        if let Level::Expect(_) = level {
            decorate(&mut err);
            err.emit();
            return;
        }

        if let Some(future_incompatible) = future_incompatible {
            let explanation = match future_incompatible.reason {
                FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps
                | FutureIncompatibilityReason::FutureReleaseErrorReportInDeps => {
                    "this was previously accepted by the compiler but is being phased out; \
                         it will become a hard error in a future release!"
                        .to_owned()
                }
                FutureIncompatibilityReason::FutureReleaseSemanticsChange => {
                    "this will change its meaning in a future release!".to_owned()
                }
                FutureIncompatibilityReason::EditionError(edition) => {
                    let current_edition = sess.edition();
                    format!(
                        "this is accepted in the current edition (Rust {current_edition}) but is a hard error in Rust {edition}!"
                    )
                }
                FutureIncompatibilityReason::EditionSemanticsChange(edition) => {
                    format!("this changes meaning in Rust {edition}")
                }
                FutureIncompatibilityReason::Custom(reason) => reason.to_owned(),
            };

            if future_incompatible.explain_reason {
                err.warn(explanation);
            }
            if !future_incompatible.reference.is_empty() {
                let citation =
                    format!("for more information, see {}", future_incompatible.reference);
                err.note(citation);
            }
        }

        // Finally, run `decorate`.
        decorate(&mut err);
        explain_lint_level_source(lint, level, src, &mut err);
        err.emit()
    }
    lint_level_impl(sess, lint, level, src, span, msg, Box::new(decorate))
}

/// Returns whether `span` originates in a foreign crate's external macro.
///
/// This is used to test whether a lint should not even begin to figure out whether it should
/// be reported on the current node.
pub fn in_external_macro(sess: &Session, span: Span) -> bool {
    let expn_data = span.ctxt().outer_expn_data();
    match expn_data.kind {
        ExpnKind::Root
        | ExpnKind::Desugaring(
            DesugaringKind::ForLoop
            | DesugaringKind::WhileLoop
            | DesugaringKind::OpaqueTy
            | DesugaringKind::Async
            | DesugaringKind::Await,
        ) => false,
        ExpnKind::AstPass(_) | ExpnKind::Desugaring(_) => true, // well, it's "external"
        ExpnKind::Macro(MacroKind::Bang, _) => {
            // Dummy span for the `def_site` means it's an external macro.
            expn_data.def_site.is_dummy() || sess.source_map().is_imported(expn_data.def_site)
        }
        ExpnKind::Macro { .. } => true, // definitely a plugin
    }
}

/// Return whether `span` is generated by `async` or `await`.
pub fn is_from_async_await(span: Span) -> bool {
    let expn_data = span.ctxt().outer_expn_data();
    match expn_data.kind {
        ExpnKind::Desugaring(DesugaringKind::Async | DesugaringKind::Await) => true,
        _ => false,
    }
}