Fixes for csharp-ts-mode fontification (bug#79406)

- hightlight reserved keywords agressively, dont allow misuse as
  variables etc (the compiler will fail!)
- highlight lambda-valued variables as funtions.
- improve semantics of function/class annotations using attributes
  (maps closer to using-something than declaring it). also: rename to
  "attribute". "property" has a different, defined meaning in C#.
- better highlight variable-use in different scenarios (function-calls,
  if-statements, assignment-expressions, property-use, anonymous object
  initializers).
- better highlight for property-use (anonymous object initializers).
- highlight field-declaration using font-lock-variable-face.
- fontify attributes using new face csharp-ts-mode-attribute-face
  (defaults to font-lock-property-use-face).
- remove extensive use of "override" making evalutation hard-to-reason about.

* lisp/progmodes/csharp-mode.el (csharp-ts-mode--indent-rules):
Update indent rules.
(csharp-ts-mode-faces): New group.
(csharp-ts-mode-attribute-face): New face.
(csharp-ts-mode--font-lock-settings): Rule updates.
(csharp-ts-mode): Change property feature to attribute

2 files changed, 76 insertions, 19 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 1a54de9de2e..1d8e85f7d1a 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -972,6 +972,12 @@ are highlighted like other comments.  When non-nil, Doxygen comment
 blocks are syntax-highlighted if the Doxygen grammar library is
 available.
 
+** Csharp-ts-mode
+
+*** Renamed feature in 'treesit-font-lock-feature-list'
+The feature 'property' has been renamed to 'attribute', since this is
+what it is called in the general C# community.
+
 ** Go-ts mode
 
 +++
diff --git a/lisp/progmodes/csharp-mode.el b/lisp/progmodes/csharp-mode.el
index 0c44fff18bf..d8b20e1f6f0 100644
--- a/lisp/progmodes/csharp-mode.el
+++ b/lisp/progmodes/csharp-mode.el
@@ -673,7 +673,7 @@ compilation and evaluation time conflicts."
      ((parent-is "namespace_declaration") parent-bol 0)
      ((parent-is "class_declaration") parent-bol 0)
      ((parent-is "constructor_declaration") parent-bol 0)
-     ((parent-is "array_creation_expression") parent-bol 0) ;; actual initialization is in contained initializer_expression
+     ((parent-is "array_creation_expression") parent-bol 0) ;; actual initialization is in contained initializer_expression.
      ((match "{" "initializer_expression" ) parent-bol 0)
      ((parent-is "initializer_expression") parent-bol csharp-ts-mode-indent-offset)
      ((match "{" "anonymous_object_creation_expression") parent-bol 0)
@@ -735,6 +735,15 @@ compilation and evaluation time conflicts."
     "readonly" "unmanaged")
   "C# keywords for tree-sitter font-locking.")
 
+(defgroup csharp-ts-mode-faces nil
+  "Font faces."
+  :group 'cshap)
+
+(defface csharp-ts-mode-attribute-face
+  '((t . (:inherit font-lock-property-use-face)))
+  "Font face used for fontification of attributes."
+  :group 'csharp-ts-mode-faces)
+
 (defun csharp-ts-mode--test-this-expression ()
   "Return non-nil if (this_expression) is named in csharp grammar."
   (treesit-query-valid-p 'c-sharp "(this_expression)"))
@@ -782,6 +791,18 @@ compilation and evaluation time conflicts."
    '((conditional_expression (identifier) @font-lock-variable-use-face)
      (postfix_unary_expression (identifier)* @font-lock-variable-use-face)
      (initializer_expression (assignment_expression left: (identifier) @font-lock-property-use-face))
+     (anonymous_object_creation_expression
+      (identifier) @font-lock-property-use-face
+      (identifier) @font-lock-variable-use-face)
+     (anonymous_object_creation_expression
+      (identifier) @font-lock-property-use-face
+      [(object_creation_expression)
+       (integer_literal)
+       (string_literal)
+       (binary_expression)
+       (invocation_expression)
+       (member_access_expression)
+       (conditional_expression)])
      (interpolated_string_expression
       (interpolation
        (identifier) @font-lock-variable-use-face))
@@ -823,7 +844,24 @@ compilation and evaluation time conflicts."
       (:match "^[a-z][A-Za-z0-9]+" @font-lock-variable-use-face))
      ((binary_expression
        right: (identifier) @font-lock-variable-use-face)
-      (:match "^[a-z][A-Za-z0-9]+" @font-lock-variable-use-face)))
+      (:match "^[a-z][A-Za-z0-9]+" @font-lock-variable-use-face))
+     (assignment_expression
+      right: (identifier) @font-lock-variable-use-face)
+     (expression_statement ;; capture parent node to NOT shadow variable_declaration.
+      (assignment_expression
+       left: (identifier) @font-lock-variable-use-face))
+     (if_statement condition: (identifier) @font-lock-variable-use-face)
+
+     ;; handle more specific matchers before generalized variable-use fallback.
+     (invocation_expression
+      function: (member_access_expression
+                 name: (identifier) @font-lock-function-call-face))
+     (invocation_expression
+      function: (member_access_expression
+                 name: (generic_name (identifier) @font-lock-function-call-face)))
+     (member_access_expression
+      expression: (identifier) @font-lock-variable-use-face
+      name: (identifier) @font-lock-property-use-face))
 
    :language 'c-sharp
    :feature 'bracket
@@ -849,13 +887,19 @@ compilation and evaluation time conflicts."
      (modifier) @font-lock-keyword-face
      ,@(if (csharp-ts-mode--test-this-expression)
            '((this_expression) @font-lock-keyword-face)
-         '("this" @font-lock-keyword-face)))
+         '("this" @font-lock-keyword-face))
+
+     ;; avoid fontifying indentifiers with a keyword-values as identifiers.
+     ((identifier) @font-lock-keyword-face
+      (:match ,(concat "\\`" (regexp-opt csharp-ts-mode--keywords t) "\\'") @font-lock-keyword-face)))
 
    :language 'c-sharp
    :override t
-   :feature 'property
-   `((attribute (identifier) @font-lock-property-use-face (attribute_argument_list))
-     (attribute (identifier) @font-lock-property-use-face))
+   :feature 'attribute
+   `((attribute_list
+      "[" @csharp-ts-mode-attribute-face
+      (attribute name: (identifier) @csharp-ts-mode-attribute-face)
+      "]" @csharp-ts-mode-attribute-face))
 
    :language 'c-sharp
    :override t
@@ -890,7 +934,6 @@ compilation and evaluation time conflicts."
      @font-lock-string-face)
 
    :language 'c-sharp
-   :override t
    :feature 'type
    `((predefined_type) @font-lock-type-face
      (implicit_type) @font-lock-type-face
@@ -935,7 +978,6 @@ compilation and evaluation time conflicts."
 
    :language 'c-sharp
    :feature 'definition
-   :override t
    `((qualified_name (identifier) @font-lock-type-face)
      (using_directive (identifier) @font-lock-type-face)
      ,@(when (csharp-ts-mode--test-name-equals)
@@ -944,6 +986,8 @@ compilation and evaluation time conflicts."
 
      (enum_declaration (identifier) @font-lock-type-face)
      (enum_member_declaration (identifier) @font-lock-variable-name-face)
+     (field_declaration (variable_declaration (variable_declarator
+        name: (identifier) @font-lock-variable-name-face)))
 
      (interface_declaration (identifier) @font-lock-type-face)
 
@@ -974,6 +1018,18 @@ compilation and evaluation time conflicts."
      (method_declaration ,csharp-ts-mode--type-field (generic_name (identifier) @font-lock-type-face))
      (method_declaration name: (_) @font-lock-function-name-face)
 
+     ;; only fontify known expression-types, to avoid the need to use :override
+     ;; for lambda-expressions in 'function below.
+     (variable_declarator
+      name: (identifier) @font-lock-variable-name-face
+      [(object_creation_expression)
+       (integer_literal)
+       (string_literal)
+       (binary_expression)
+       (invocation_expression)
+       (member_access_expression)
+       (conditional_expression)])
+
      (catch_declaration
       ((identifier) @font-lock-type-face))
      (catch_declaration
@@ -984,7 +1040,6 @@ compilation and evaluation time conflicts."
      (variable_declaration (qualified_name
                             name: (generic_name (identifier) @font-lock-type-face)))
      (variable_declaration (generic_name (identifier) @font-lock-type-face))
-     (variable_declarator (identifier) @font-lock-variable-name-face)
 
      (parameter type: (identifier) @font-lock-type-face)
      (parameter type: (generic_name (identifier) @font-lock-type-face))
@@ -1001,14 +1056,6 @@ compilation and evaluation time conflicts."
    :feature 'function
    '((invocation_expression
       function: (identifier) @font-lock-function-call-face)
-     (invocation_expression
-      function: (member_access_expression
-                 name: (identifier) @font-lock-function-call-face))
-     (invocation_expression
-      function: (member_access_expression
-                 name: (generic_name (identifier) @font-lock-function-call-face)))
-     (invocation_expression
-      function: (generic_name (identifier) @font-lock-function-call-face))
      ((invocation_expression
        function: (member_access_expression
                   expression: (identifier) @font-lock-variable-use-face))
@@ -1018,7 +1065,11 @@ compilation and evaluation time conflicts."
                  expression: (identifier) @font-lock-variable-use-face))
       (:match "^[a-z][A-Za-z0-9]+" @font-lock-variable-use-face))
      (argument (member_access_expression
-                name: (identifier) @font-lock-property-use-face)))
+                name: (identifier) @font-lock-property-use-face))
+     ;; only highlight as function if variable contains lambda expression
+     (variable_declarator
+      name: (identifier) @font-lock-function-name-face
+      (lambda_expression)))
 
    :language 'c-sharp
    :feature 'escape-sequence
@@ -1198,7 +1249,7 @@ Key bindings:
   (setq-local treesit-font-lock-feature-list
               '(( comment definition)
                 ( keyword string type directives)
-                ( constant escape-sequence expression literal property)
+                ( constant escape-sequence expression literal attribute)
                 ( function bracket delimiter error)))
 
   ;; Imenu.