Add string literal completion for equality expression

Author: mhegazy

src/services/completions.ts

@@ -173,6 +173,11 @@ namespace ts.Completions {
             //      var y = require("/*completion position*/");
             return getStringLiteralCompletionEntriesFromModuleNames(<StringLiteral>node, compilerOptions, host, typeChecker);
         }
+        else if (isEqualityExpression(node.parent)) {
+            // Get all known external module names or complete a path to a module
+            // i.e. x === '/*completion position'
+            return getStringLiteralCompletionEntriesFromBinaryExpression(<StringLiteral>node, node.parent, typeChecker);
+        }
         else {
             const argumentInfo = SignatureHelp.getImmediatelyContainingArgumentInfo(node, position, sourceFile);
             if (argumentInfo) {
@@ -240,6 +245,18 @@ namespace ts.Completions {
         return undefined;
     }
 
+    function getStringLiteralCompletionEntriesFromBinaryExpression(node: StringLiteral, parent: BinaryExpression, typeChecker: TypeChecker): CompletionInfo | undefined {
+        const type = typeChecker.getTypeAtLocation(parent.left === node ? parent.right : parent.left);
+        if (type) {
+            const entries: CompletionEntry[] = [];
+            addStringLiteralCompletionsFromType(type, entries, typeChecker);
+            if (entries.length) {
+                return { isGlobalCompletion: false, isMemberCompletion: false, isNewIdentifierLocation: false, entries };
+            }
+        }
+        return undefined;
+    }
+
     function addStringLiteralCompletionsFromType(type: Type, result: Push<CompletionEntry>, typeChecker: TypeChecker): void {
         if (type && type.flags & TypeFlags.TypeParameter) {
             type = typeChecker.getApparentType(type);
@@ -1756,4 +1773,11 @@ namespace ts.Completions {
         catch (e) {}
         return undefined;
     }
+
+    function isEqualityExpression(node: Node): node is BinaryExpression {
+        return isBinaryExpression(node) && (node.operatorToken.kind == SyntaxKind.EqualsEqualsToken ||
+            node.operatorToken.kind === SyntaxKind.ExclamationEqualsToken ||
+            node.operatorToken.kind === SyntaxKind.EqualsEqualsEqualsToken ||
+            node.operatorToken.kind === SyntaxKind.ExclamationEqualsEqualsToken);
+    }
 }

tests/cases/fourslash/completionForStringLiteral10.ts

@@ -0,0 +1,12 @@
+/// <reference path='fourslash.ts'/>
+
+////type As = 'arf' | 'abacus' | 'abaddon';
+////let a: As;
+////if ('/**/' != a
+
+goTo.marker();
+verify.completionListContains("arf");
+verify.completionListContains("abacus");
+verify.completionListContains("abaddon");
+verify.completionListCount(3);
+

tests/cases/fourslash/completionForStringLiteral8.ts

@@ -0,0 +1,12 @@
+/// <reference path='fourslash.ts'/>
+
+////type As = 'arf' | 'abacus' | 'abaddon';
+////let a: As;
+////if (a === '/**/
+
+goTo.marker();
+verify.completionListContains("arf");
+verify.completionListContains("abacus");
+verify.completionListContains("abaddon");
+verify.completionListCount(3);
+