From 75be9a1042919147178ebb9f9eec94922c2c26c5 Mon Sep 17 00:00:00 2001
From: Klaus Meinhardt <klaus.meinhardt1@gmail.com>
Date: Tue, 28 Nov 2017 17:35:44 +0100
Subject: [PATCH] prefer-const: don't treat index signatures as parameters
 (#3385)

The `k` in `{[k: string]: string}` is a `ts.ParameterDeclaration`. This should not be treated like a parameter in the value domain.
---
 src/rules/preferConstRule.ts                 | 10 ++++++----
 test/rules/prefer-const/default/test.ts.fix  |  7 +++++++
 test/rules/prefer-const/default/test.ts.lint |  7 +++++++
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/rules/preferConstRule.ts b/src/rules/preferConstRule.ts
index e66f9cbf830..984f95dd782 100644
--- a/src/rules/preferConstRule.ts
+++ b/src/rules/preferConstRule.ts
@@ -175,10 +175,12 @@ class PreferConstWalker extends Lint.AbstractWalker<Options> {
                     });
                 }
             } else if (node.kind === ts.SyntaxKind.Parameter) {
-                this.handleBindingName((node as ts.ParameterDeclaration).name, {
-                    canBeConst: false,
-                    isBlockScoped: true,
-                });
+                if (node.parent!.kind !== ts.SyntaxKind.IndexSignature) {
+                    this.handleBindingName((node as ts.ParameterDeclaration).name, {
+                        canBeConst: false,
+                        isBlockScoped: true,
+                    });
+                }
             } else if (utils.isPostfixUnaryExpression(node) ||
                        utils.isPrefixUnaryExpression(node) &&
                        (node.operator === ts.SyntaxKind.PlusPlusToken || node.operator === ts.SyntaxKind.MinusMinusToken)) {
diff --git a/test/rules/prefer-const/default/test.ts.fix b/test/rules/prefer-const/default/test.ts.fix
index e7f2b6d749d..987b880694e 100644
--- a/test/rules/prefer-const/default/test.ts.fix
+++ b/test/rules/prefer-const/default/test.ts.fix
@@ -219,3 +219,10 @@ for (let {var1, var2} of someArr) {
     var2 = null;
 }
 
+{
+    let k: any = 0;
+    function foo(param: {[k: string]: string}) {
+        k = param;
+    }
+}
+
diff --git a/test/rules/prefer-const/default/test.ts.lint b/test/rules/prefer-const/default/test.ts.lint
index acd8cee48eb..5b379fce273 100644
--- a/test/rules/prefer-const/default/test.ts.lint
+++ b/test/rules/prefer-const/default/test.ts.lint
@@ -258,6 +258,13 @@ for (let {var1, var2} of someArr) {
     var2 = null;
 }
 
+{
+    let k: any = 0;
+    function foo(param: {[k: string]: string}) {
+        k = param;
+    }
+}
+
 [_base]: Identifier '%%s' is never reassigned; use 'const' instead of '%s'.
 [let]: _base % ('let')
 [var]: _base % ('var')