prefer-const: special handling for destructuring in for-of

src/rules/preferConstRule.ts

@@ -273,7 +273,8 @@ class PreferConstWalker extends Lint.AbstractWalker<Options> {
                 canBeConst: true,
                 declarationList,
                 isBlockScoped: kind === utils.VariableDeclarationKind.Let,
-                isForLoop: declarationList.parent!.kind === ts.SyntaxKind.ForStatement,
+                isForLoop: declarationList.parent!.kind === ts.SyntaxKind.ForStatement ||
+                           declarationList.parent!.kind === ts.SyntaxKind.ForOfStatement,
                 reassignedSiblings: false,
             };
         }

test/rules/prefer-const/default/test.ts.fix

@@ -56,7 +56,7 @@ function myFunc2() {
 for (const n of [1, 1]) { // failure for 'n'
     console.log(n);
 }
-for (let {o, p} of [{1, 1}, {1, 1}]) { // failure for 'o'
+for (let {o, p} of [{1, 1}, {1, 1}]) {
     console.log(o);
     p = 2;
 }
@@ -211,4 +211,11 @@ declare namespace ambient {
     let someVar: string, someObj: any;
     for ({someVar: someObj.val} of someArr) {}
 }
+for (let [var1, var2] of someArr) {
+    var1 = null;
+}
+for (const [var1, var2] of someArr) {}
+for (let {var1, var2} of someArr) {
+    var2 = null;
+}
 

test/rules/prefer-const/default/test.ts.lint

@@ -68,8 +68,7 @@ for (let n of [1, 1]) { // failure for 'n'
          ~                                 [let % ('n')]
     console.log(n);
 }
-for (let {o, p} of [{1, 1}, {1, 1}]) { // failure for 'o'
-          ~                                               [let % ('o')]
+for (let {o, p} of [{1, 1}, {1, 1}]) {
     console.log(o);
     p = 2;
 }
@@ -249,6 +248,15 @@ declare namespace ambient {
                          ~~~~~~~ [let % ('someObj')]
     for ({someVar: someObj.val} of someArr) {}
 }
+for (let [var1, var2] of someArr) {
+    var1 = null;
+}
+for (let [var1, var2] of someArr) {}
+          ~~~~ [let % ('var1')]
+                ~~~~ [let % ('var2')]
+for (let {var1, var2} of someArr) {
+    var2 = null;
+}
 
 [_base]: Identifier '%%s' is never reassigned; use 'const' instead of '%s'.
 [let]: _base % ('let')