Merge pull request github#3166 from erik-krogh/DeadLocal

Approved by asgerf

Author: semmle-qlci

javascript/ql/src/Declarations/DeadStoreOfLocal.ql

@@ -63,8 +63,10 @@ where
   (
     // To avoid confusion about the meaning of "definition" and "declaration" we avoid
     // the term "definition" when the alert location is a variable declaration.
-    if dead instanceof VariableDeclarator
+    if
+      dead instanceof VariableDeclarator and
+      not exists(SsaImplicitInit init | init.getVariable().getSourceVariable() = v) // the variable is dead at the hoisted implicit initialization.
     then msg = "The initial value of " + v.getName() + " is unused, since it is always overwritten."
-    else msg = "This definition of " + v.getName() + " is useless, since its value is never read."
+    else msg = "The value assigned to " + v.getName() + " here is unused."
   )
 select dead, msg

javascript/ql/test/query-tests/Declarations/DeadStoreOfLocal/DeadStoreOfLocal.expected

@@ -1,12 +1,13 @@
-| overload.ts:10:12:10:14 | baz | This definition of baz is useless, since its value is never read. |
+| overload.ts:10:12:10:14 | baz | The value assigned to baz here is unused. |
 | tst2.js:26:9:26:14 | x = 23 | The initial value of x is unused, since it is always overwritten. |
-| tst2.js:28:9:28:14 | x = 42 | This definition of x is useless, since its value is never read. |
-| tst3.js:2:1:2:36 | exports ... a: 23 } | This definition of exports is useless, since its value is never read. |
-| tst3b.js:2:18:2:36 | exports = { a: 23 } | This definition of exports is useless, since its value is never read. |
-| tst.js:6:2:6:7 | y = 23 | This definition of y is useless, since its value is never read. |
+| tst2.js:28:9:28:14 | x = 42 | The value assigned to x here is unused. |
+| tst3.js:2:1:2:36 | exports ... a: 23 } | The value assigned to exports here is unused. |
+| tst3b.js:2:18:2:36 | exports = { a: 23 } | The value assigned to exports here is unused. |
+| tst.js:6:2:6:7 | y = 23 | The value assigned to y here is unused. |
 | tst.js:13:6:13:11 | a = 23 | The initial value of a is unused, since it is always overwritten. |
-| tst.js:13:14:13:19 | a = 42 | This definition of a is useless, since its value is never read. |
+| tst.js:13:14:13:19 | a = 42 | The value assigned to a here is unused. |
 | tst.js:45:6:45:11 | x = 23 | The initial value of x is unused, since it is always overwritten. |
 | tst.js:51:6:51:11 | x = 23 | The initial value of x is unused, since it is always overwritten. |
 | tst.js:132:7:132:13 | {x} = o | The initial value of x is unused, since it is always overwritten. |
 | tst.js:162:6:162:14 | [x] = [0] | The initial value of x is unused, since it is always overwritten. |
+| tst.js:172:7:172:17 | nSign = foo | The value assigned to nSign here is unused. |

javascript/ql/test/query-tests/Declarations/DeadStoreOfLocal/tst.js

@@ -166,3 +166,11 @@ function v() {
 	x;
 	y;
 });
+
+(function() {
+	if (something()) {
+		var nSign = foo;
+	} else {
+		console.log(nSign);
+	}
+})()