Fix #131977 parens mangled in shared mut static lint suggestion

compiler/rustc_lint/src/static_mut_refs.rs

@@ -3,8 +3,8 @@
 use rustc_middle::ty::{Mutability, TyKind};
 use rustc_session::lint::FutureIncompatibilityReason;
 use rustc_session::{declare_lint, declare_lint_pass};
-use rustc_span::Span;
 use rustc_span::edition::Edition;
+use rustc_span::{BytePos, Span};
 
 use crate::lints::{MutRefSugg, RefOfMutStatic};
 use crate::{LateContext, LateLintPass, LintContext};
@@ -71,13 +71,24 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
                 if matches!(borrow_kind, hir::BorrowKind::Ref)
                     && let Some(err_span) = path_is_static_mut(ex, err_span) =>
             {
-                emit_static_mut_refs(
-                    cx,
-                    err_span,
-                    err_span.with_hi(ex.span.lo()),
-                    m,
-                    !expr.span.from_expansion(),
-                );
+                let source_map = cx.sess().source_map();
+                let snippet = source_map.span_to_snippet(err_span);
+
+                let sugg_span = if let Ok(snippet) = snippet {
+                    // ( ( &IDENT ) )
+                    // ~~~~ exclude these from the suggestion span to avoid unmatching parens
+                    let exclude_n_bytes: u32 = snippet
+                        .chars()
+                        .take_while(|ch| ch.is_whitespace() || *ch == '(')
+                        .map(|ch| ch.len_utf8() as u32)
+                        .sum();
+
+                    err_span.with_lo(err_span.lo() + BytePos(exclude_n_bytes)).with_hi(ex.span.lo())
+                } else {
+                    err_span.with_hi(ex.span.lo())
+                };
+
+                emit_static_mut_refs(cx, err_span, sugg_span, m, !expr.span.from_expansion());
             }
             hir::ExprKind::MethodCall(_, e, _, _)
                 if let Some(err_span) = path_is_static_mut(e, expr.span)

tests/ui/statics/static-mut-shared-parens.rs

@@ -0,0 +1,13 @@
+//Missing paren in diagnostic msg: https://github.com/rust-lang/rust/issues/131977
+//@check-pass
+
+
+static mut TEST: usize = 0;
+
+fn main() {
+    let _ = unsafe { (&TEST) as *const usize };
+    //~^WARN creating a shared reference to mutable static is discouraged
+
+    let _ = unsafe { ((&mut TEST)) as *const usize };
+    //~^WARN creating a mutable reference to mutable static is discouraged
+}

tests/ui/statics/static-mut-shared-parens.stderr

@@ -0,0 +1,29 @@
+warning: creating a shared reference to mutable static is discouraged
+  --> $DIR/static-mut-shared-parens.rs:8:22
+   |
+LL |     let _ = unsafe { (&TEST) as *const usize };
+   |                      ^^^^^^^ shared reference to mutable static
+   |
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
+   = note: shared references to mutable statics are dangerous; it's undefined behavior if the static is mutated or if a mutable reference is created for it while the shared reference lives
+   = note: `#[warn(static_mut_refs)]` on by default
+help: use `&raw const` instead to create a raw pointer
+   |
+LL |     let _ = unsafe { (&raw const TEST) as *const usize };
+   |                       ~~~~~~~~~~
+
+warning: creating a mutable reference to mutable static is discouraged
+  --> $DIR/static-mut-shared-parens.rs:11:22
+   |
+LL |     let _ = unsafe { ((&mut TEST)) as *const usize };
+   |                      ^^^^^^^^^^^^^ mutable reference to mutable static
+   |
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
+   = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives
+help: use `&raw mut` instead to create a raw pointer
+   |
+LL |     let _ = unsafe { ((&raw mut TEST)) as *const usize };
+   |                        ~~~~~~~~
+
+warning: 2 warnings emitted
+