basic lint v2 implemented

compiler/rustc_lint/messages.ftl

@@ -494,6 +494,8 @@ 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_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

@@ -3,14 +3,14 @@
 
 use crate::lints::{
     BadOptAccessDiag, DefaultHashTypesDiag, DiagOutOfImpl, LintPassByHand, NonExistentDocKeyword,
-    QueryInstability, TyQualified, TykindDiag, TykindKind, UntranslatableDiag,
+    QueryInstability, SpanUseEqCtxtDiag, TyQualified, TykindDiag, TykindKind, UntranslatableDiag,
     UntranslatableDiagnosticTrivial,
 };
 use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
 use rustc_ast as ast;
 use rustc_hir::def::Res;
 use rustc_hir::{def_id::DefId, Expr, ExprKind, GenericArg, PatKind, Path, PathSegment, QPath};
-use rustc_hir::{HirId, Impl, Item, ItemKind, Node, Pat, Ty, TyKind};
+use rustc_hir::{BinOp, BinOpKind, HirId, Impl, Item, ItemKind, Node, Pat, Ty, TyKind};
 use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::hygiene::{ExpnKind, MacroKind};
@@ -537,3 +537,44 @@ 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?
+    "Use of `==` with `Span::ctxt` rather than `Span::eq_ctxt`",
+    report_in_external_macro: true
+}
+
+declare_lint_pass!(SpanUseEqCtxt => [SPAN_USE_EQ_CTXT]);
+
+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" },
+                );
+            }
+        }
+    }
+}
+
+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))
+        }
+
+        _ => false,
+    }
+}

compiler/rustc_lint/src/lib.rs

@@ -83,7 +83,6 @@ mod passes;
 mod ptr_nulls;
 mod redundant_semicolon;
 mod reference_casting;
-mod span_use_eq_ctxt;
 mod traits;
 mod types;
 mod unused;
@@ -532,6 +531,8 @@ fn register_internals(store: &mut LintStore) {
     store.register_late_mod_pass(|_| Box::new(BadOptAccess));
     store.register_lints(&PassByValue::get_lints());
     store.register_late_mod_pass(|_| Box::new(PassByValue));
+    store.register_lints(&SpanUseEqCtxt::get_lints());
+    store.register_late_mod_pass(|_| Box::new(SpanUseEqCtxt));
     // FIXME(davidtwco): deliberately do not include `UNTRANSLATABLE_DIAGNOSTIC` and
     // `DIAGNOSTIC_OUTSIDE_OF_IMPL` here because `-Wrustc::internal` is provided to every crate and
     // these lints will trigger all of the time - change this once migration to diagnostic structs
@@ -549,6 +550,7 @@ fn register_internals(store: &mut LintStore) {
             LintId::of(USAGE_OF_QUALIFIED_TY),
             LintId::of(EXISTING_DOC_KEYWORD),
             LintId::of(BAD_OPT_ACCESS),
+            LintId::of(SPAN_USE_EQ_CTXT),
         ],
     );
 }

compiler/rustc_lint/src/lints.rs

@@ -900,6 +900,12 @@ pub struct QueryInstability {
     pub query: Symbol,
 }
 
+#[derive(LintDiagnostic)]
+#[diag(lint_span_use_eq_ctxt)]
+pub struct SpanUseEqCtxtDiag<'a> {
+    pub msg: &'a str,
+}
+
 #[derive(LintDiagnostic)]
 #[diag(lint_tykind_kind)]
 pub struct TykindKind {

compiler/rustc_lint/src/span_use_eq_ctxt.rs

@@ -1,38 +0,0 @@
-use crate::{LateContext, LateLintPass};
-use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind};
-use rustc_span::sym;
-
-declare_lint! {
-    pub SPAN_USE_EQ_CTXT,
-    Warn, // is this the right level?
-    "Use of `==` with `Span::ctxt` rather than `Span::eq_ctxt`"
-}
-
-declare_lint_pass!(SpanUseEqCtxt => [SPAN_USE_EQ_CTXT]);
-
-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) {
-                todo!(); // emit lint
-            }
-        }
-    }
-}
-
-fn is_span_ctxt_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
-    match &expr.kind {
-        ExprKind::MethodCall(..) => {
-            // i gave a method a diagnostic item -- FIXME: switch to a diagnostic
-            // item for the Span type and check:
-            //   * method call path == "ctxt"
-            //   * receiver type matches Span diag item
-            // also FIXME(todo) remove old SpanCtxt diagnostic item
-            cx.typeck_results()
-                .type_dependent_def_id(expr.hir_id)
-                .is_some_and(|did| cx.tcx.is_diagnostic_item(sym::SpanCtxt, did))
-        }
-
-        _ => false,
-    }
-}

compiler/rustc_span/src/span_encoding.rs

@@ -75,6 +75,7 @@ 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 {
@@ -212,7 +213,6 @@ 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`.
-    #[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,
-        SpanCtxt,
+        Span,
         String,
         StructuralEq,
         StructuralPartialEq,

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

@@ -0,0 +1,13 @@
+// compile-flags: -Z unstable-options
+
+#![feature(rustc_private)]
+#![deny(rustc::span_use_eq_ctxt)]
+
+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
+}
+
+fn main() {}