Account for macro invocation in let mut $pat diagnostic.

src/libsyntax/parse/parser/pat.rs

@@ -4,7 +4,7 @@ use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
 use crate::ptr::P;
 use crate::ast::{self, Attribute, Pat, PatKind, FieldPat, RangeEnd, RangeSyntax, Mac};
 use crate::ast::{BindingMode, Ident, Mutability, Path, QSelf, Expr, ExprKind};
-use crate::mut_visit::{noop_visit_pat, MutVisitor};
+use crate::mut_visit::{noop_visit_pat, noop_visit_mac, MutVisitor};
 use crate::parse::token::{self};
 use crate::print::pprust;
 use crate::source_map::{respan, Span, Spanned};
@@ -481,6 +481,10 @@ impl<'a> Parser<'a> {
     fn make_all_value_bindings_mutable(pat: &mut P<Pat>) -> bool {
         struct AddMut(bool);
         impl MutVisitor for AddMut {
+            fn visit_mac(&mut self, mac: &mut Mac) {
+                noop_visit_mac(mac, self);
+            }
+
             fn visit_pat(&mut self, pat: &mut P<Pat>) {
                 if let PatKind::Ident(BindingMode::ByValue(ref mut m @ Mutability::Immutable), ..)
                     = pat.kind

src/test/ui/parser/issue-65122-mac-invoc-in-mut-patterns.rs

@@ -0,0 +1,26 @@
+// Regression test; used to ICE with 'visit_mac disabled by default' due to a
+// `MutVisitor` in `fn make_all_value_bindings_mutable` (`parse/parser/pat.rs`).
+
+macro_rules! mac1 {
+    ($eval:expr) => {
+        let mut $eval = ();
+        //~^ ERROR `mut` must be followed by a named binding
+    };
+}
+
+macro_rules! mac2 {
+    ($eval:pat) => {
+        let mut $eval = ();
+        //~^ ERROR `mut` must be followed by a named binding
+        //~| ERROR expected identifier, found `does_not_exist!()`
+    };
+}
+
+fn foo() {
+    mac1! { does_not_exist!() }
+    //~^ ERROR cannot find macro `does_not_exist` in this scope
+    mac2! { does_not_exist!() }
+    //~^ ERROR cannot find macro `does_not_exist` in this scope
+}
+
+fn main() {}

src/test/ui/parser/issue-65122-mac-invoc-in-mut-patterns.stderr

@@ -0,0 +1,45 @@
+error: `mut` must be followed by a named binding
+  --> $DIR/issue-65122-mac-invoc-in-mut-patterns.rs:6:13
+   |
+LL |         let mut $eval = ();
+   |             ^^^^^^^^^ help: remove the `mut` prefix: `does_not_exist!()`
+...
+LL |     mac1! { does_not_exist!() }
+   |     --------------------------- in this macro invocation
+   |
+   = note: `mut` may be followed by `variable` and `variable @ pattern`
+
+error: expected identifier, found `does_not_exist!()`
+  --> $DIR/issue-65122-mac-invoc-in-mut-patterns.rs:13:17
+   |
+LL |         let mut $eval = ();
+   |                 ^^^^^ expected identifier
+...
+LL |     mac2! { does_not_exist!() }
+   |     --------------------------- in this macro invocation
+
+error: `mut` must be followed by a named binding
+  --> $DIR/issue-65122-mac-invoc-in-mut-patterns.rs:13:13
+   |
+LL |         let mut $eval = ();
+   |             ^^^ help: remove the `mut` prefix: `does_not_exist!()`
+...
+LL |     mac2! { does_not_exist!() }
+   |     --------------------------- in this macro invocation
+   |
+   = note: `mut` may be followed by `variable` and `variable @ pattern`
+
+error: cannot find macro `does_not_exist` in this scope
+  --> $DIR/issue-65122-mac-invoc-in-mut-patterns.rs:20:13
+   |
+LL |     mac1! { does_not_exist!() }
+   |             ^^^^^^^^^^^^^^
+
+error: cannot find macro `does_not_exist` in this scope
+  --> $DIR/issue-65122-mac-invoc-in-mut-patterns.rs:22:13
+   |
+LL |     mac2! { does_not_exist!() }
+   |             ^^^^^^^^^^^^^^
+
+error: aborting due to 5 previous errors
+