Merge #1077

1077: Improve parsing of type bounds r=matklad a=vipentti

This adds new TYPE_BOUND_LIST and TYPE_BOUND syntax kinds. These are now used when parsing type bounds. In addition parsing paths inside a bound now does not recursively parse paths, rather they are treated as separate bounds, separated by +.

Basically now the generic params `struct S<T: 'a + ?Sized + (Copy)>;` in will be parsed as 

```
TYPE_PARAM_LIST@[8; 33)
  L_ANGLE@[8; 9)
  TYPE_PARAM@[9; 32)
    NAME@[9; 10)
      IDENT@[9; 10) "T"
    COLON@[10; 11)
    WHITESPACE@[11; 12)
    TYPE_BOUND_LIST@[12; 32)
      TYPE_BOUND@[12; 14)
        LIFETIME@[12; 14) "'a"
      WHITESPACE@[14; 15)
      PLUS@[15; 16)
      WHITESPACE@[16; 17)
      TYPE_BOUND@[17; 23)
        QUESTION@[17; 18)
        PATH_TYPE@[18; 23)
          PATH@[18; 23)
            PATH_SEGMENT@[18; 23)
              NAME_REF@[18; 23)
                IDENT@[18; 23) "Sized"
      WHITESPACE@[23; 24)
      PLUS@[24; 25)
      WHITESPACE@[25; 26)
      TYPE_BOUND@[26; 32)
        L_PAREN@[26; 27)
        PATH_TYPE@[27; 31)
          PATH@[27; 31)
            PATH_SEGMENT@[27; 31)
              NAME_REF@[27; 31)
                IDENT@[27; 31) "Copy"
        R_PAREN@[31; 32)
  R_ANGLE@[32; 33)
```

Previously it was parsed, with the paths nested:

```
TYPE_PARAM_LIST@[8; 33)
  L_ANGLE@[8; 9)
  TYPE_PARAM@[9; 32)
    NAME@[9; 10)
      IDENT@[9; 10) "T"
    COLON@[10; 11)
    WHITESPACE@[11; 12)
    LIFETIME@[12; 14) "'a"
    WHITESPACE@[14; 15)
    PLUS@[15; 16)
    WHITESPACE@[16; 17)
    QUESTION@[17; 18)
    PATH_TYPE@[18; 32)
      PATH@[18; 23)
        PATH_SEGMENT@[18; 23)
          NAME_REF@[18; 23)
            IDENT@[18; 23) "Sized"
      WHITESPACE@[23; 24)
      PLUS@[24; 25)
      WHITESPACE@[25; 26)
      L_PAREN@[26; 27)
      PATH_TYPE@[27; 31)
        PATH@[27; 31)
          PATH_SEGMENT@[27; 31)
            NAME_REF@[27; 31)
              IDENT@[27; 31) "Copy"
      R_PAREN@[31; 32)
  R_ANGLE@[32; 33)
```

Looking for feedback.



Co-authored-by: Ville Penttinen <[email protected]>

1 files changed, 33 insertions, 7 deletions

diff --git a/crates/ra_parser/src/grammar/types.rs b/crates/ra_parser/src/grammar/types.rs
index fdd4f2c52..a46da9b44 100644
--- a/crates/ra_parser/src/grammar/types.rs
+++ b/crates/ra_parser/src/grammar/types.rs
@@ -261,21 +261,47 @@ fn path_or_macro_type_(p: &mut Parser, allow_bounds: bool) {
         PATH_TYPE
     };
 
-    if allow_bounds && p.eat(PLUS) {
-        type_params::bounds_without_colon(p);
-    }
+    let path = m.complete(p, kind);
 
-    m.complete(p, kind);
+    if allow_bounds {
+        opt_path_type_bounds_as_dyn_trait_type(p, path);
+    }
 }
 
 pub(super) fn path_type_(p: &mut Parser, allow_bounds: bool) {
     assert!(paths::is_path_start(p) || p.at(L_ANGLE));
     let m = p.start();
     paths::type_path(p);
+
     // test path_type_with_bounds
     // fn foo() -> Box<T + 'f> {}
-    if allow_bounds && p.eat(PLUS) {
-        type_params::bounds_without_colon(p);
+    // fn foo() -> Box<dyn T + 'f> {}
+    let path = m.complete(p, PATH_TYPE);
+    if allow_bounds {
+        opt_path_type_bounds_as_dyn_trait_type(p, path);
     }
-    m.complete(p, PATH_TYPE);
+}
+
+/// This turns a parsed PATH_TYPE optionally into a DYN_TRAIT_TYPE
+/// with a TYPE_BOUND_LIST
+fn opt_path_type_bounds_as_dyn_trait_type(p: &mut Parser, path_type_marker: CompletedMarker) {
+    if !p.at(PLUS) {
+        return;
+    }
+
+    // First create a TYPE_BOUND from the completed PATH_TYPE
+    let m = path_type_marker.precede(p).complete(p, TYPE_BOUND);
+
+    // Next setup a marker for the TYPE_BOUND_LIST
+    let m = m.precede(p);
+
+    // This gets consumed here so it gets properly set
+    // in the TYPE_BOUND_LIST
+    p.eat(PLUS);
+
+    // Parse rest of the bounds into the TYPE_BOUND_LIST
+    let m = type_params::bounds_without_colon_m(p, m);
+
+    // Finally precede everything with DYN_TRAIT_TYPE
+    m.precede(p).complete(p, DYN_TRAIT_TYPE);
 }