debug Span::ctxt() call detection

compiler/rustc_hir_typeck/src/callee.rs

@@ -650,7 +650,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .sess
                 .source_map()
                 .is_multiline(call_expr.span.with_lo(callee_expr.span.hi()))
-                && call_expr.span.ctxt() == callee_expr.span.ctxt();
+                && call_expr.span.eq_ctxt(callee_expr.span);
             if call_is_multiline {
                 err.span_suggestion(
                     callee_expr.span.shrink_to_hi(),

compiler/rustc_lint/messages.ftl

@@ -494,7 +494,7 @@ lint_renamed_lint = lint `{$name}` has been renamed to `{$replace}`
 
 lint_requested_level = requested on the command line with `{$level} {$lint_name}`
 
-lint_span_use_eq_ctxt = use `eq_ctxt()` not `ctxt() == ctxt()`
+lint_span_use_eq_ctxt = use `.eq_ctxt()` instead of `.ctxt() == .ctxt()`
 
 lint_supertrait_as_deref_target = `{$t}` implements `Deref` with supertrait `{$target_principal}` as target
     .label = target type is set here

compiler/rustc_lint/src/internal.rs

@@ -538,13 +538,9 @@ impl LateLintPass<'_> for BadOptAccess {
     }
 }
 
-// some things i'm not sure about:
-//   * is Warn the right level?
-//   * the way i verify that the right method is being called (path + diag item check)
-
 declare_tool_lint! {
     pub rustc::SPAN_USE_EQ_CTXT,
-    Warn, // is this the right level?
+    Allow,
     "Use of `==` with `Span::ctxt` rather than `Span::eq_ctxt`",
     report_in_external_macro: true
 }
@@ -555,11 +551,7 @@ impl<'tcx> LateLintPass<'tcx> for SpanUseEqCtxt {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
         if let ExprKind::Binary(BinOp { node: BinOpKind::Eq, .. }, lhs, rhs) = expr.kind {
             if is_span_ctxt_call(cx, lhs) && is_span_ctxt_call(cx, rhs) {
-                cx.emit_spanned_lint(
-                    SPAN_USE_EQ_CTXT,
-                    expr.span,
-                    SpanUseEqCtxtDiag { msg: "fail" },
-                );
+                cx.emit_spanned_lint(SPAN_USE_EQ_CTXT, expr.span, SpanUseEqCtxtDiag);
             }
         }
     }
@@ -567,13 +559,10 @@ impl<'tcx> LateLintPass<'tcx> for SpanUseEqCtxt {
 
 fn is_span_ctxt_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     match &expr.kind {
-        ExprKind::MethodCall(path, receiver, _, _) => {
-            path.ident.name.as_str() == "ctxt"
-                && cx
-                    .typeck_results()
-                    .type_dependent_def_id(receiver.hir_id)
-                    .is_some_and(|did| cx.tcx.is_diagnostic_item(sym::Span, did))
-        }
+        ExprKind::MethodCall(..) => cx
+            .typeck_results()
+            .type_dependent_def_id(expr.hir_id)
+            .is_some_and(|call_did| cx.tcx.is_diagnostic_item(sym::SpanCtxt, call_did)),
 
         _ => false,
     }

compiler/rustc_lint/src/lints.rs

@@ -902,9 +902,7 @@ pub struct QueryInstability {
 
 #[derive(LintDiagnostic)]
 #[diag(lint_span_use_eq_ctxt)]
-pub struct SpanUseEqCtxtDiag<'a> {
-    pub msg: &'a str,
-}
+pub struct SpanUseEqCtxtDiag;
 
 #[derive(LintDiagnostic)]
 #[diag(lint_tykind_kind)]

compiler/rustc_mir_transform/src/coverage/spans.rs

@@ -404,7 +404,7 @@ impl<'a> CoverageSpansGenerator<'a> {
 
         let Some(visible_macro) = curr.visible_macro(self.body_span) else { return };
         if let Some(prev) = &self.some_prev
-            && prev.expn_span.ctxt() == curr.expn_span.ctxt()
+            && prev.expn_span.eq_ctxt(curr.expn_span)
         {
             return;
         }

compiler/rustc_span/src/span_encoding.rs

@@ -75,7 +75,6 @@ use rustc_data_structures::fx::FxIndexSet;
 /// the dependency to the parent definition's span. This is performed
 /// using the callback `SPAN_TRACK` to access the query engine.
 ///
-#[cfg_attr(not(test), rustc_diagnostic_item = "Span")]
 #[derive(Clone, Copy, Eq, PartialEq, Hash)]
 #[rustc_pass_by_value]
 pub struct Span {
@@ -213,6 +212,7 @@ impl Span {
 
     /// This function is used as a fast path when decoding the full `SpanData` is not necessary.
     /// It's a cut-down version of `data_untracked`.
+    #[cfg_attr(not(test), rustc_diagnostic_item = "SpanCtxt")]
     #[inline]
     pub fn ctxt(self) -> SyntaxContext {
         if self.len_with_tag_or_marker != BASE_LEN_INTERNED_MARKER {

compiler/rustc_span/src/symbol.rs

@@ -303,7 +303,7 @@ symbols! {
         SliceIndex,
         SliceIter,
         Some,
-        Span,
+        SpanCtxt,
         String,
         StructuralEq,
         StructuralPartialEq,

tests/ui-fulldeps/internal-lints/span_use_eq_ctxt.rs

@@ -1,13 +1,13 @@
+// Test the `rustc::span_use_eq_ctxt` internal lint
 // compile-flags: -Z unstable-options
 
 #![feature(rustc_private)]
 #![deny(rustc::span_use_eq_ctxt)]
+#![crate_type = "lib"]
 
 extern crate rustc_span;
 use rustc_span::Span;
 
 pub fn f(s: Span, t: Span) -> bool {
-    s.ctxt() == t.ctxt() //~ ERROR use of span ctxt
+    s.ctxt() == t.ctxt() //~ ERROR use `.eq_ctxt()` instead of `.ctxt() == .ctxt()`
 }
-
-fn main() {}

tests/ui-fulldeps/internal-lints/span_use_eq_ctxt.stderr

@@ -0,0 +1,14 @@
+error: use `.eq_ctxt()` instead of `.ctxt() == .ctxt()`
+  --> $DIR/span_use_eq_ctxt.rs:12:5
+   |
+LL |     s.ctxt() == t.ctxt()
+   |     ^^^^^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/span_use_eq_ctxt.rs:5:9
+   |
+LL | #![deny(rustc::span_use_eq_ctxt)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+