Account for const fn with type params calls in const expr recovery

Author: estebank

src/librustc_parse/parser/path.rs

@@ -456,8 +456,10 @@ impl<'a> Parser<'a> {
                 }
             })
             .is_some();
-        // This will be true when a trait object type `Foo +` has been parsed.
-        let was_op = self.prev_token.kind == token::BinOp(token::Plus);
+        // This will be true when a trait object type `Foo +` or a path which was a `const fn` with
+        // type params has been parsed.
+        let was_op =
+            matches!(self.prev_token.kind, token::BinOp(token::Plus | token::Shr) | token::Gt);
         if !is_op && !was_op {
             // We perform these checks and early return to avoid taking a snapshot unnecessarily.
             return Err(err);

src/test/ui/const-generics/const-expression-missing-braces.rs

@@ -27,4 +27,27 @@ fn e() {
 fn f() {
     foo::<100 - BAR>(); // ok
 }
+fn g() {
+    foo::<bar<i32>()>(); //~ ERROR expected one of
+}
+fn h() {
+    foo::<bar::<i32>()>(); //~ ERROR expected one of
+}
+fn i() {
+    foo::<bar::<i32>() + BAR>(); //~ ERROR expected one of
+}
+fn j() {
+    foo::<bar::<i32>() - BAR>(); //~ ERROR expected one of
+}
+fn k() {
+    foo::<BAR - bar::<i32>()>(); //~ ERROR expected one of
+}
+fn l() {
+    foo::<BAR - bar::<i32>()>(); //~ ERROR expected one of
+}
+
+const fn bar<const C: usize>() -> usize {
+    C
+}
+
 fn main() {}

src/test/ui/const-generics/const-expression-missing-braces.stderr

@@ -31,6 +31,72 @@ help: to write a `const` expression, surround it with braces for it to be unambi
 LL |     foo::<{ BAR - BAR }>();
    |           ^           ^
 
+error: expected one of `,` or `>`, found `(`
+  --> $DIR/const-expression-missing-braces.rs:31:19
+   |
+LL |     foo::<bar<i32>()>();
+   |                   ^ expected one of `,` or `>`
+   |
+help: to write a `const` expression, surround it with braces for it to be unambiguous
+   |
+LL |     foo::<{ bar<i32>() }>();
+   |           ^            ^
+
+error: expected one of `,` or `>`, found `(`
+  --> $DIR/const-expression-missing-braces.rs:34:21
+   |
+LL |     foo::<bar::<i32>()>();
+   |                     ^ expected one of `,` or `>`
+   |
+help: to write a `const` expression, surround it with braces for it to be unambiguous
+   |
+LL |     foo::<{ bar::<i32>() }>();
+   |           ^              ^
+
+error: expected one of `,` or `>`, found `(`
+  --> $DIR/const-expression-missing-braces.rs:37:21
+   |
+LL |     foo::<bar::<i32>() + BAR>();
+   |                     ^ expected one of `,` or `>`
+   |
+help: to write a `const` expression, surround it with braces for it to be unambiguous
+   |
+LL |     foo::<{ bar::<i32>() + BAR }>();
+   |           ^                    ^
+
+error: expected one of `,` or `>`, found `(`
+  --> $DIR/const-expression-missing-braces.rs:40:21
+   |
+LL |     foo::<bar::<i32>() - BAR>();
+   |                     ^ expected one of `,` or `>`
+   |
+help: to write a `const` expression, surround it with braces for it to be unambiguous
+   |
+LL |     foo::<{ bar::<i32>() - BAR }>();
+   |           ^                    ^
+
+error: expected one of `,` or `>`, found `-`
+  --> $DIR/const-expression-missing-braces.rs:43:15
+   |
+LL |     foo::<BAR - bar::<i32>()>();
+   |               ^ expected one of `,` or `>`
+   |
+help: to write a `const` expression, surround it with braces for it to be unambiguous
+   |
+LL |     foo::<{ BAR - bar::<i32>() }>();
+   |           ^                    ^
+
+error: expected one of `,` or `>`, found `-`
+  --> $DIR/const-expression-missing-braces.rs:46:15
+   |
+LL |     foo::<BAR - bar::<i32>()>();
+   |               ^ expected one of `,` or `>`
+   |
+help: to write a `const` expression, surround it with braces for it to be unambiguous
+   |
+LL |     foo::<{ BAR - bar::<i32>() }>();
+   |           ^                    ^
+
 error: likely `const` expression parsed as trait bounds
   --> $DIR/const-expression-missing-braces.rs:13:11
    |
@@ -42,5 +108,5 @@ help: if you meant to write a `const` expression, surround the expression with b
 LL |     foo::<{ BAR + BAR }>();
    |           ^           ^
 
-error: aborting due to 4 previous errors
+error: aborting due to 10 previous errors