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, 23 insertions, 5 deletions

diff --git a/crates/ra_syntax/src/grammar.ron b/crates/ra_syntax/src/grammar.ron
index ad6d74162..18730a894 100644
--- a/crates/ra_syntax/src/grammar.ron
+++ b/crates/ra_syntax/src/grammar.ron
@@ -243,6 +243,8 @@ Grammar(
         "PARAM",
         "SELF_PARAM",
         "ARG_LIST",
+        "TYPE_BOUND",
+        "TYPE_BOUND_LIST",
     ],
     ast: {
         "SourceFile": (
@@ -293,7 +295,7 @@ Grammar(
         "EnumVariantList": ( collections: [["variants", "EnumVariant"]] ),
         "EnumVariant": ( traits: ["NameOwner", "DocCommentsOwner", "AttrsOwner"], options: ["Expr"] ),
         "TraitDef": (
-            traits: ["VisibilityOwner", "NameOwner", "AttrsOwner", "DocCommentsOwner", "TypeParamsOwner"],
+            traits: ["VisibilityOwner", "NameOwner", "AttrsOwner", "DocCommentsOwner", "TypeParamsOwner", "TypeBoundsOwner"],
             options: ["ItemList"]
         ),
         "Module": (
@@ -330,7 +332,8 @@ Grammar(
                 "NameOwner",
                 "TypeParamsOwner",
                 "AttrsOwner",
-                "DocCommentsOwner"
+                "DocCommentsOwner",
+                "TypeBoundsOwner",
             ],
             options: ["TypeRef"]
         ),
@@ -347,8 +350,12 @@ Grammar(
         "PlaceholderType": (),
         "FnPointerType": (options: ["ParamList", "RetType"]),
         "ForType": (options: ["TypeRef"]),
-        "ImplTraitType": (),
-        "DynTraitType": (),
+        "ImplTraitType": (
+            traits: ["TypeBoundsOwner"],
+        ),
+        "DynTraitType": (
+            traits: ["TypeBoundsOwner"],
+        ),
 
         "TypeRef": ( enum: [
             "ParenType",
@@ -571,12 +578,23 @@ Grammar(
                 ["lifetime_params", "LifetimeParam" ],
             ]
         ),
-        "TypeParam": ( traits: ["NameOwner", "AttrsOwner"] ),
+        "TypeParam": ( traits: ["NameOwner", "AttrsOwner", "TypeBoundsOwner"] ),
         "LifetimeParam": (
             options: [ "Lifetime"],
             traits: ["AttrsOwner"],
         ),
         "Lifetime": ( traits: ["AstToken"] ),
+        "TypeBound": (
+            options: [
+                "TypeRef",
+                "Lifetime",
+            ]
+        ),
+        "TypeBoundList": (
+            collections: [
+                ["bounds", "TypeBound"],
+            ]
+        ),
         "WhereClause": (),
         "ExprStmt": (
             options: [ ["expr", "Expr"] ]