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, 7 insertions, 5 deletions

diff --git a/crates/ra_syntax/tests/data/parser/ok/0038_where_pred_type.txt b/crates/ra_syntax/tests/data/parser/ok/0038_where_pred_type.txt
index 4842e9b90..fe3fca5cd 100644
--- a/crates/ra_syntax/tests/data/parser/ok/0038_where_pred_type.txt
+++ b/crates/ra_syntax/tests/data/parser/ok/0038_where_pred_type.txt
@@ -29,11 +29,13 @@ SOURCE_FILE@[0; 34)
           R_PAREN@[25; 26)
         COLON@[26; 27)
         WHITESPACE@[27; 28)
-        PATH_TYPE@[28; 31)
-          PATH@[28; 31)
-            PATH_SEGMENT@[28; 31)
-              NAME_REF@[28; 31)
-                IDENT@[28; 31) "Foo"
+        TYPE_BOUND_LIST@[28; 31)
+          TYPE_BOUND@[28; 31)
+            PATH_TYPE@[28; 31)
+              PATH@[28; 31)
+                PATH_SEGMENT@[28; 31)
+                  NAME_REF@[28; 31)
+                    IDENT@[28; 31) "Foo"
     WHITESPACE@[31; 32)
     BLOCK@[32; 34)
       L_CURLY@[32; 33)