Fix false error when placeholder used as part of a rule

Fixes microsoft#59

Author: mjbvz

e2e/tests/errors.js

@@ -257,13 +257,26 @@ describe('Errors', () => {
 
     it('should not return an error for a placeholder as the declaration name (#52)', () => {
         return getSemanticDiagnosticsForFile(
-            `function css(strings, ...) { return ""; }; const value = 1; const q = css\`
+            `function css(strings, ...) { return ""; }; const q = css\`
             $\{'width'}: 1px;
         \``
         ).then(errorResponse => {
             assert.isTrue(errorResponse.success);
             assert.strictEqual(errorResponse.body.length, 0);
         });
     });
+
+    it('should not return an error for a placeholder as part of a rule (#59)', () => {
+        return getSemanticDiagnosticsForFile(
+            `function css(strings, ...) { return ""; }; const q = css\`
+                $\{'a'}, \${'button'} {
+                    width: 1px;
+                }
+        \``
+        ).then(errorResponse => {
+            assert.isTrue(errorResponse.success);
+            assert.strictEqual(errorResponse.body.length, 0);
+        });
+    });
 });
 

src/substituter.ts

@@ -73,7 +73,7 @@ function getReplacementCharacter(
     post: string
 ) {
     if (pre.match(/(^|\n)\s*$/g)) {
-        if (!post.match(/^\s*[\{\:]/)) {  // ${'button'} {
+        if (!post.match(/^\s*[{:,]/)) {  // ${'button'} {
             return ' ';
         }
     }

src/test/substituter.test.ts

@@ -87,6 +87,21 @@ describe('substituter', () => {
             ].join('\n')
         );
     });
+
+    it('should insert x for placeholder used as part of a rule (#59)', () => {
+        assert.deepEqual(
+            performSubstitutions([
+                '${"button"}, ${"a"} {',
+                'color: ${"red"};',
+                '}',
+            ].join('\n')),
+            [
+                'xxxxxxxxxxx, xxxxxx {',
+                'color: xxxxxxxx;',
+                '}',
+            ].join('\n')
+        );
+    });
 });
 
 function performSubstitutions(value: string) {