Fix highlighting of package and project names in variable references.

There are ambiguities in variable references (such as Foo'Bar) where
it's ambiguous whether this is a reference to attribute Bar in package
Foo of the current project or a reference to a top-level attribute Bar
in project Foo.  Another ambiguity is Foo.X'Bar, as it's unclear if X
is a package in project Foo with attribute Bar or if Foo.X is a child
project and Bar is a top-level attribute of the child project.  This
issue applies to variable references as well the variable attribute
references demonstrated above, since variables can be declared both at
the project level as well as within a package.

These ambiguities can't be resolved by the syntax tree itself and
would require active checking of package declaration names in the file
or project references (with, extends, etc.) or maintaining a list of
known package names.

If we can't correctly identify package names in variable references,
that leaves a highlighting inconsistency where package declaration
names would be highlighted, but variable references wouldn't.  This
would mean that for consistency, all package name highlighting would
need to be removed.

None of these options are ideal.  Package name highlighting gives
visual cues to the reader, indicating if a variable attribute
reference is for a package or a project.  Since it seems useful for
the user to distinguish this information, the option to maintain a
list of known packages is implemented.  This list is a user option
which contains the currently known package names, however if custom
packages are created, this list can easily be updated.

README.org

@@ -162,6 +162,30 @@ the different font lock levels.
 - Level 3 :: attribute, function, number, operator, package, variable
 - Level 4 :: bracket, delimiter, error
 
+The following user options can be customized to modify the syntax
+highlighting characteristics:
+
+- User Option: gpr-ts-mode-package-names :: List of known package
+  names to highlight within variable references.  There are
+  ambiguities in the syntax tree for variable references.  For
+  example, ~Foo'Bar~ could be a reference to the ~Bar~ attribute in the
+  package ~Foo~ of the current project, or it could be a reference to
+  the top-level ~Bar~ attribute in the project ~Foo~.  There are
+  additional ambiguities when child packages are involved since
+  references such as ~Foo.X'Bar~ exhibit the same problem.  This
+  ambiguity applies not just to variable attribute references but also
+  to regular variable references since variables can exist at the
+  project level as well as within a package.  If package names in
+  variable references are not properly highlighted, this causes an
+  inconsistency between highlighting of package names in package
+  declarations and not properly highlighting package names in variable
+  references.  Actively monitoring package names in the current
+  project as well as all withed projects is considered too heavy
+  handed and instead we settle for maintaining a list of package
+  names.  Since custom package names can be introduced (although
+  uncommon), the list of names can be customized, but is initialized
+  with the set of well-known names.
+
 * Indentation
 
 Indentation follows the nesting structure of the language.  Each

doc/gpr-ts-mode.texi

@@ -235,6 +235,32 @@ attribute, function, number, operator, package, variable
 bracket, delimiter, error
 @end table
 
+The following user options can be customized to modify the syntax
+highlighting characteristics:
+
+@defopt gpr-ts-mode-package-names
+List of known package
+  names to highlight within variable references.  There are
+  ambiguities in the syntax tree for variable references.  For
+  example, @code{Foo'Bar} could be a reference to the @code{Bar} attribute in the
+  package @code{Foo} of the current project, or it could be a reference to
+  the top-level @code{Bar} attribute in the project @code{Foo}.  There are
+  additional ambiguities when child packages are involved since
+  references such as @code{Foo.X'Bar} exhibit the same problem.  This
+  ambiguity applies not just to variable attribute references but also
+  to regular variable references since variables can exist at the
+  project level as well as within a package.  If package names in
+  variable references are not properly highlighted, this causes an
+  inconsistency between highlighting of package names in package
+  declarations and not properly highlighting package names in variable
+  references.  Actively monitoring package names in the current
+  project as well as all withed projects is considered too heavy
+  handed and instead we settle for maintaining a list of package
+  names.  Since custom package names can be introduced (although
+  uncommon), the list of names can be customized, but is initialized
+  with the set of well-known names.
+@end defopt
+
 @node Indentation
 @chapter Indentation
 
@@ -403,4 +429,4 @@ and configuration of recommended supporting packages and modes.
 
 @printindex vr
 
-@bye
+@bye

gpr-ts-mode.el

@@ -1,10 +1,10 @@
 ;;; gpr-ts-mode.el --- Major mode for GNAT project files using Tree-Sitter  -*- lexical-binding: t; -*-
 
-;; Copyright (C) 2023 Troy Brown
+;; Copyright (C) 2023-2024 Troy Brown
 
 ;; Author: Troy Brown <[email protected]>
 ;; Created: February 2023
-;; Version: 0.5.4
+;; Version: 0.5.5
 ;; Keywords: gpr gnat ada languages tree-sitter
 ;; URL: https://github.com/brownts/gpr-ts-mode
 ;; Package-Requires: ((emacs "29.1"))
@@ -111,6 +111,17 @@ specified.  See `treesit-language-source-alist' for full details."
   :link '(custom-manual :tag "Grammar Installation" "(gpr-ts-mode)Grammar Installation")
   :package-version "0.5.0")
 
+(defcustom gpr-ts-mode-package-names
+  '("binder" "builder" "check" "clean" "compiler" "cross_reference"
+    "documentation" "eliminate" "finder" "gnatls" "gnatstub"
+    "ide" "install" "linker" "metrics" "naming" "pretty_printer"
+    "remote" "stack" "synchronize")
+  "List of known package names."
+  :type '(repeat string)
+  :group 'gpr-ts
+  :link '(custom-manual :tag "Syntax Highlighting" "(gpr-ts-mode)Syntax Highlighting")
+  :package-version "0.5.5")
+
 (defvar gpr-ts-mode-syntax-table
   (let ((table (make-syntax-table)))
     (modify-syntax-entry ?-  ". 12" table)
@@ -472,7 +483,8 @@ Return nil if no child of that type is found."
    '((package_declaration
       [ origname: (name (identifier) @font-lock-function-call-face :anchor)
         basename: (name (identifier) @font-lock-function-call-face :anchor)])
-     (variable_reference (name (identifier) @font-lock-function-call-face :anchor) "'"))
+     ((variable_reference (name (identifier) @font-lock-function-call-face))
+      (:pred gpr-ts-mode--package-name-p @font-lock-function-call-face)))
 
    ;; String literals
    :language 'gpr
@@ -487,6 +499,7 @@ Return nil if no child of that type is found."
    ;; Variables
    :language 'gpr
    :feature 'variable
+   :override t
    '((variable_reference (name (identifier) @font-lock-variable-use-face :anchor) :anchor))
 
    ;; Operators
@@ -502,6 +515,13 @@ Return nil if no child of that type is found."
 
   "Font-lock settings for `gpr-ts-mode'.")
 
+(defun gpr-ts-mode--package-name-p (node)
+  "Check if NODE identifier matches a known package name."
+  (let ((identifier (downcase (treesit-node-text node t)))
+        (packages (mapcar #'downcase gpr-ts-mode-package-names)))
+    (seq-find (apply-partially #'string-equal identifier) packages)))
+
+
 ;;; Imenu
 
 (defun gpr-ts-mode--defun-name (node)

test/gpr-ts-mode-tests.el

@@ -20,6 +20,7 @@
 ;;; Code:
 
 (require 'ert)
+(require 'ert-font-lock nil 'noerror) ; Emacs 30+
 (require 'ert-x)
 (require 'gpr-ts-mode)
 (require 'treesit)
@@ -102,8 +103,15 @@ otherwise check that there is no error in the parse tree."
                           ((string-prefix-p "filling" file-noext) #'filling-transform)
                           ((string-prefix-p "indent" file-noext) #'indent-transform)
                           (t #'default-transform))))
-    (eval `(ert-deftest ,(intern (concat "gpr-ts-mode-test-" file-noext)) ()
-             (ert-test-erts-file ,file-path #',transform)))))
+    (if (string-prefix-p "font-lock" file-noext)
+        (eval `(ert-deftest ,(intern (concat "gpr-ts-mode-" file-noext)) ()
+                 (skip-unless (featurep 'ert-font-lock))
+                 (with-temp-buffer
+                   (insert-file-contents ,file-path)
+                   (funcall #',transform))
+                 (ert-font-lock-test-file ,file-path 'gpr-ts-mode)))
+      (eval `(ert-deftest ,(intern (concat "gpr-ts-mode-test-" file-noext)) ()
+               (ert-test-erts-file ,file-path #',transform))))))
 
 (provide 'gpr-ts-mode-tests)
 

test/resources/font-lock-variable_reference.gpr

@@ -0,0 +1,49 @@
+with "shared";
+
+project Test is
+
+   for Source_Dirs use Shared'Source_Dirs &
+                         -- <- nil
+                         --   ^ font-lock-property-use-face
+                         Test'Source_Dirs &
+                         -- <- nil
+                         --   ^ font-lock-property-use-face
+                         Project'Source_Dirs;
+   --                    ^ nil
+   --                            ^ font-lock-property-use-face
+
+   package Compiler is
+      for Default_Switches ("Ada") use Compiler'Default_Switches ("Ada") & ("-gnata");
+      --                               ^ font-lock-function-call-face
+      --                                        ^ font-lock-property-use-face
+
+      for Default_Switches ("Ada") use Shared.Compiler'Default_Switches ("Ada");
+      --                               ^ nil
+      --                                      ^ font-lock-function-call-face
+      --                                               ^ font-lock-property-use-face
+
+      for Default_Switches ("Ada") use Shared.Child.Compiler'Default_Switches ("Ada");
+      --                               ^      ^ nil
+      --                                            ^ font-lock-function-call-face
+      --                                                     ^ font-lock-property-use-face
+
+      for Default_Switches ("Ada") use Compiler.My_Switches;
+      --                               ^ font-lock-function-call-face
+      --                                        ^ font-lock-variable-use-face
+
+      for Default_Switches ("Ada") use Shared.My_Switches;
+      --                               ^ nil
+      --                                      ^ font-lock-variable-use-face
+
+      for Default_Switches ("Ada") use Shared.Compiler.My_Switches;
+      --                               ^ nil
+      --                                      ^ font-lock-function-call-face
+      --                                               ^ font-lock-variable-use-face
+
+      for Default_Switches ("Ada") use Shared.Child.Compiler.My_Switches;
+      --                               ^      ^ nil
+      --                                            ^ font-lock-function-call-face
+      --                                                     ^ font-lock-variable-use-face
+   end Compiler;
+
+end Test;