Fixed cast expression parsing in ra_syntax.

The cast expression expected any type via types::type_() function,
but the language spec does only allow TypeNoBounds (types without direct extra bounds
via `+`).

**Example:**

```rust
fn test() {
	6i8 as i32 + 5;
}
```

This fails, because the types::type_() function which should parse the type after the
as keyword is greedy, and takes all plus sign after path types as extra.

My proposed fix is to replace the not implemented `type_no_plus()` just calls (`type_()`)
function, which is used at several places. The replacement is `type_with_bounds_cond(p: &mut Parser, allow_bounds: bool)`, which passes the condition to relevant sub-parsers.

This function is then called by `type_()` and the new public `type_no_bounds()`.

2 files changed, 18 insertions, 9 deletions

diff --git a/crates/ra_syntax/src/grammar/expressions.rs b/crates/ra_syntax/src/grammar/expressions.rs
index 60c8602f9..a9449c7bf 100644
--- a/crates/ra_syntax/src/grammar/expressions.rs
+++ b/crates/ra_syntax/src/grammar/expressions.rs
@@ -368,12 +368,16 @@ fn try_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
 // test cast_expr
 // fn foo() {
 //     82 as i32;
+//     81 as i8 + 1;
+//     79 as i16 - 1;
 // }
 fn cast_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
     assert!(p.at(AS_KW));
     let m = lhs.precede(p);
     p.bump();
-    types::type_(p);
+    // Use type_no_bounds(), because cast expressions are not
+    // allowed to have bounds.
+    types::type_no_bounds(p);
     m.complete(p, CAST_EXPR)
 }
 
diff --git a/crates/ra_syntax/src/grammar/types.rs b/crates/ra_syntax/src/grammar/types.rs
index ed2718e73..811d399d4 100644
--- a/crates/ra_syntax/src/grammar/types.rs
+++ b/crates/ra_syntax/src/grammar/types.rs
@@ -11,6 +11,14 @@ pub(super) const TYPE_FIRST: TokenSet = token_set_union![
 const TYPE_RECOVERY_SET: TokenSet = token_set![R_PAREN, COMMA];
 
 pub(super) fn type_(p: &mut Parser) {
+    type_with_bounds_cond(p, true);
+}
+
+pub(super) fn type_no_bounds(p: &mut Parser) {
+    type_with_bounds_cond(p, false);
+}
+
+fn type_with_bounds_cond(p: &mut Parser, allow_bounds: bool) {
     match p.current() {
         L_PAREN => paren_or_tuple_type(p),
         EXCL => never_type(p),
@@ -22,8 +30,9 @@ pub(super) fn type_(p: &mut Parser) {
         FOR_KW => for_type(p),
         IMPL_KW => impl_trait_type(p),
         DYN_KW => dyn_trait_type(p),
-        L_ANGLE => path_type(p),
-        _ if paths::is_path_start(p) => path_type(p),
+        // Some path types are not allowed to have bounds (no plus)
+        L_ANGLE => path_type_(p, allow_bounds),
+        _ if paths::is_path_start(p) => path_type_(p, allow_bounds),
         _ => {
             p.err_recover("expected type", TYPE_RECOVERY_SET);
         }
@@ -35,10 +44,6 @@ pub(super) fn ascription(p: &mut Parser) {
     type_(p)
 }
 
-fn type_no_plus(p: &mut Parser) {
-    type_(p);
-}
-
 fn paren_or_tuple_type(p: &mut Parser) {
     assert!(p.at(L_PAREN));
     let m = p.start();
@@ -101,7 +106,7 @@ fn pointer_type(p: &mut Parser) {
         }
     };
 
-    type_no_plus(p);
+    type_no_bounds(p);
     m.complete(p, POINTER_TYPE);
 }
 
@@ -147,7 +152,7 @@ fn reference_type(p: &mut Parser) {
     p.bump();
     p.eat(LIFETIME);
     p.eat(MUT_KW);
-    type_no_plus(p);
+    type_no_bounds(p);
     m.complete(p, REFERENCE_TYPE);
 }