rust highlights: clean up constructor logic (helix-editor#8957)

Enum variants and (tuple) structs are indistinguishable in general, so we
mark any PascalCase pattern or expression as a "constructor", which
covers all three.

runtime/queries/rust/highlights.scm

@@ -189,6 +189,33 @@
 
 ; TODO: variable.mut to highlight mutable identifiers via locals.scm
 
+; -------
+; Constructors
+; -------
+; TODO: this is largely guesswork, remove it once we get actual info from locals.scm or r-a
+
+(struct_expression
+  name: (type_identifier) @constructor)
+
+(tuple_struct_pattern
+  type: [
+    (identifier) @constructor
+    (scoped_identifier
+      name: (identifier) @constructor)
+  ])
+(struct_pattern
+  type: [
+    ((type_identifier) @constructor)
+    (scoped_type_identifier
+      name: (type_identifier) @constructor)
+  ])
+(match_pattern
+  ((identifier) @constructor) (#match? @constructor "^[A-Z]"))
+(or_pattern
+  ((identifier) @constructor)
+  ((identifier) @constructor)
+  (#match? @constructor "^[A-Z]"))
+
 ; -------
 ; Guess Other Types
 ; -------
@@ -203,33 +230,28 @@
 
 (call_expression
   function: [
-    ((identifier) @type.enum.variant
-      (#match? @type.enum.variant "^[A-Z]"))
+    ((identifier) @constructor
+      (#match? @constructor "^[A-Z]"))
     (scoped_identifier
-      name: ((identifier) @type.enum.variant
-        (#match? @type.enum.variant "^[A-Z]")))
+      name: ((identifier) @constructor
+        (#match? @constructor "^[A-Z]")))
   ])
 
 ; ---
-; Assume that types in match arms are enums and not
-; tuple structs. Same for `if let` expressions.
+; PascalCase identifiers under a path which is also PascalCase
+; are assumed to be constructors if they have methods or fields.
 ; ---
 
-(match_pattern
-    (scoped_identifier
-      name: (identifier) @constructor))
-(tuple_struct_pattern
-    type: [
-      ((identifier) @constructor)
-      (scoped_identifier  
-        name: (identifier) @constructor)
-      ])
-(struct_pattern
-  type: [
-    ((type_identifier) @constructor)
-    (scoped_type_identifier
-      name: (type_identifier) @constructor)
-    ])
+(field_expression
+  value: (scoped_identifier
+    path: [
+      (identifier) @type
+      (scoped_identifier
+        name: (identifier) @type)
+    ]
+    name: (identifier) @constructor
+      (#match? @type "^[A-Z]")
+      (#match? @constructor "^[A-Z]")))
 
 ; ---
 ; Other PascalCase identifiers are assumed to be structs.