Add support for custom @import modifier functions (#2)

This commit adds patterns to scope function calls of unknown names
within import at-rules, as PostCSS can add additional language features
via plugins' custom parsers.

Author: deathaxe

PostCSS.sublime-syntax

@@ -57,6 +57,14 @@ contexts:
     - include: postcss-variable-definitions
     - include: postcss-variables
 
+  at-import-body:
+    - meta_prepend: true
+    - match: (?:(?!layer|supports|url){{ident}})(?=\()
+      scope: meta.function-call.identifier.css variable.function.css
+      push:
+        - other-function-arguments-list-body
+        - function-arguments-list-begin
+
   at-other:
     - meta_prepend: true
     - include: postcss-at-apply

tests/syntax_test_scope.postcss

@@ -24,6 +24,25 @@
 //        ^^^ variable.other.postcss
 //           ^ punctuation.section.interpolation.end.postcss
 
+/*
+ * import at-rules
+ */
+
+    @import "url" prefix(tw);
+//^^^^^^^^^^^^^^^^^^^^^^^^^^^ source.css.postcss
+//  ^^^^^^^^^^^^^^^^^^^^^^^^ meta.at-rule.import.css
+//  ^^^^^^^ keyword.control.directive.css
+//  ^ punctuation.definition.keyword.css
+//          ^^^^^ meta.string.css string.quoted.double.css
+//          ^ punctuation.definition.string.begin.css
+//              ^ punctuation.definition.string.end.css
+//                ^^^^^^ variable.function.css
+//                      ^^^^ meta.function-call.arguments.css meta.group.css
+//                      ^ punctuation.section.group.begin.css
+//                       ^^ support.constant.property-value.css
+//                         ^ punctuation.section.group.end.css
+//                          ^ punctuation.terminator.rule.css
+
 /*
  * unknown at-rules
  */