Only suggest turbofish in patterns if we may recover

Author: fmease

compiler/rustc_parse/src/parser/pat.rs

@@ -830,7 +830,8 @@ impl<'a> Parser<'a> {
     ) -> PResult<'a, PatKind> {
         let ident = self.parse_ident()?;
 
-        if !matches!(syntax_loc, Some(PatternLocation::FunctionParameter))
+        if self.may_recover()
+            && !matches!(syntax_loc, Some(PatternLocation::FunctionParameter))
             && self.check_noexpect(&token::Lt)
             && self.look_ahead(1, |t| t.can_begin_type())
         {

tests/ui/parser/issues/issue-115780-pat-lt-bracket-in-macro-call.rs

@@ -0,0 +1,21 @@
+// Regression test for issue #115780.
+// Ensure that we don't emit a parse error for the token sequence `Ident "<" Ty` in pattern position
+// if we are inside a macro call since it can be valid input for a subsequent macro rule.
+// See also #103534.
+
+// check-pass
+
+macro_rules! mdo {
+    ($p: pat =<< $e: expr ; $( $t: tt )*) => {
+        $e.and_then(|$p| mdo! { $( $t )* })
+    };
+    (ret<$ty: ty> $e: expr;) => { Some::<$ty>($e) };
+}
+
+fn main() {
+    mdo! {
+        x_val =<< Some(0);
+        y_val =<< Some(1);
+        ret<(i32, i32)> (x_val, y_val);
+    };
+}