Syntax: Add highlighting for extends values

Add special scopes for `extends`'s values to be able to provide completions
and easily identify/find them.

Author: deathaxe

Package/Sublime Text Syntax Definition/Sublime Text Syntax Definition.sublime-syntax

@@ -133,6 +133,7 @@ contexts:
       captures:
         1: string.unquoted.plain.out.yaml storage.type.extends.sublime-syntax
         2: punctuation.separator.key-value.yaml
+      push: expect_extends_list
 
     - match: ((?:hidden_)?file_extensions)\s*(:)(?=\s|$)
       captures:
@@ -162,6 +163,52 @@ contexts:
 
     - include: scope:source.yaml
 
+  expect_extends_list:
+    - meta_content_scope: meta.extends.sublime-syntax
+    - include: comment
+    - include: yaml-tags-anchors
+    # array-like context list
+    - match: \[
+      scope: punctuation.definition.array.begin.sublime-syntax
+      set:
+        - meta_scope: meta.extends.sublime-syntax meta.flow-sequence.yaml
+        - match: \]
+          scope: punctuation.definition.array.end.sublime-syntax
+          pop: true
+        - match: ','
+          scope: punctuation.separator.array-element.sublime-syntax
+        - match: '{{plain_scalar_but_not_block_key}}'
+          push: extended_syntax_file
+        - include: comment
+        - include: yaml-tags-anchors
+    # multi-line context list
+    - match: ^([ ]+)(?=-\s*{{plain_scalar_but_not_block_key}})
+      set:
+        - meta_scope: meta.extends.sublime-syntax meta.block-sequence.yaml
+        # pop off at none-empty line with different indention than first item
+        - match: ^(?!(\s*$|\1-))
+          pop: true
+        - match: '{{plain_scalar_but_not_block_key}}'
+          push: extended_syntax_file
+        - include: comment
+        - include: yaml-block-sequence
+        - match: \S.*$
+          scope: invalid.illegal.extends.sublime-syntax
+    # maybe single include
+    - match: '{{plain_scalar_but_not_block_key}}'
+      set:
+        - meta_scope: meta.extends.sublime-syntax meta.path.sublime-syntax string.unquoted.plain.out.yaml
+        - include: extended_syntax_file
+    - match: ^\s*$
+      pop: 1
+
+  extended_syntax_file:
+    - meta_scope: meta.path.sublime-syntax string.unquoted.plain.out.yaml
+    - match: '{{_flow_scalar_end_plain_in}}'
+      pop: true
+    - match: /
+      scope: punctuation.separator.path.sublime-syntax
+
   variables_block:
     - meta_scope: meta.block.variables.sublime-syntax
     - include: comment

Package/Sublime Text Syntax Definition/syntax_test_sublime-syntax.yaml

@@ -13,7 +13,26 @@ version: 2
 extends: Packages/Default/Text.sublime-syntax
 #^^^^^^ string.unquoted.plain.out.yaml storage.type.extends.sublime-syntax
 #      ^ punctuation.separator.key-value.yaml
-#        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ string.unquoted.plain.out.yaml
+#       ^ meta.extends - meta.path
+#        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ meta.extends.sublime-syntax meta.path.sublime-syntax string.unquoted.plain.out.yaml
+#                ^ punctuation.separator.path.sublime-syntax
+#                        ^ punctuation.separator.path.sublime-syntax
+#                                            ^ - meta.extends - meta.path
+extends: [ Text.sublime-syntax , Source.sublime-syntax ]
+#        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ meta.extends.sublime-syntax meta.flow-sequence.yaml
+#         ^ - meta.path
+#          ^^^^^^^^^^^^^^^^^^^ meta.path.sublime-syntax string.unquoted.plain.out.yaml
+#                             ^^^ - meta.path
+#                                ^^^^^^^^^^^^^^^^^^^^^ meta.path.sublime-syntax string.unquoted.plain.out.yaml
+#                                                     ^^ - meta.path
+extends:
+  - Packages/Default/Text.sublime-syntax
+# <- meta.extends.sublime-syntax meta.block-sequence.yaml
+#^^^ meta.extends.sublime-syntax meta.block-sequence.yaml
+#   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ meta.extends.sublime-syntax meta.block-sequence.yaml meta.path.sublime-syntax string.unquoted.plain.out.yaml
+#           ^ punctuation.separator.path.sublime-syntax
+#                   ^ punctuation.separator.path.sublime-syntax
+#                                       ^ meta.extends.sublime-syntax meta.block-sequence.yaml - meta.path
 file_extensions: [a, b]
 #^^^^^^^^^^^^^^ string.unquoted.plain.out.yaml entity.name.tag.yaml
 #                ^^^^^^ meta.flow-sequence.yaml, meta.sequence.flow.yaml