(GH-1336) Add syntax folding for braces and brackets

This commit adds detection of text regions bounded by braces { } and brackets
( ).  This provides syntax aware folding for functions, arrays and hash tables.

Author: glennsarti

src/features/Folding.ts

@@ -159,10 +159,47 @@ export class FoldingProvider implements vscode.FoldingRangeProvider {
         return foldingRanges;
     }
 
+    // Given a start and end textmate scope name, find matching grammar tokens
+    // and pair them together.  Uses a simple FIFO stack to take into account
+    // nested regions.
+    private matchScopeElements(tokens,
+                               startScopeName: string,
+                               endScopeName: string,
+                               matchType: MatchType,
+                               document: vscode.TextDocument): IMatchedTokenList {
+        const result = [];
+        const tokenStack = [];
+
+        tokens.forEach((token) => {
+            if (token.scopes.includes(startScopeName)) {
+                tokenStack.push(token);
+            }
+            if (token.scopes.includes(endScopeName)) {
+                result.push(new MatchedToken(tokenStack.pop(), token, null, null, matchType, document));
+            }
+        });
+
+        return result.reverse();
+    }
+
     // Given a list of tokens, return a list of matched tokens/line numbers regions
     private matchGrammarTokens(tokens, document: vscode.TextDocument): IMatchedTokenList {
         const matchedTokens = [];
 
+        // Find matching Braces   { -> }
+        this.matchScopeElements(tokens,
+                                "punctuation.section.braces.begin.powershell",
+                                "punctuation.section.braces.end.powershell",
+                                MatchType.Region, document)
+            .forEach((x) => { matchedTokens.push(x); });
+
+        // Find matching brackets   ( -> )
+        this.matchScopeElements(tokens,
+                                "punctuation.section.group.begin.powershell",
+                                "punctuation.section.group.end.powershell",
+                                MatchType.Region, document)
+            .forEach((x) => { matchedTokens.push(x); });
+
         return matchedTokens;
     }