JS: Avoid duplicate alerts

Author: asgerf

javascript/ql/src/LanguageFeatures/NonLinearPattern.ql

@@ -14,12 +14,35 @@
 
 import javascript
 
-from BindingPattern p, string n, VarDecl v, VarDecl w
+class RootDestructuringPattern extends BindingPattern {
+  RootDestructuringPattern() {
+    this instanceof DestructuringPattern and
+    not this = any(PropertyPattern p).getValuePattern() and
+    not this = any(ArrayPattern p).getAnElement()
+  }
+
+  /** Holds if this pattern has multiple bindings for `name`. */
+  predicate hasConflictingBindings(string name) {
+    exists(VarRef v, VarRef w |
+      v = getABindingVarRef() and
+      w = getABindingVarRef() and
+      name = v.getName() and
+      name = w.getName() and
+      v != w
+    )
+  }
+
+  /** Gets the first occurrence of the conflicting binding `name`. */
+  VarDecl getFirstClobberedVarDecl(string name) {
+    hasConflictingBindings(name) and
+    result = min(VarDecl decl | decl = getABindingVarRef() and decl.getName() = name | decl order by decl.getLocation().getStartLine(), decl.getLocation().getStartColumn())
+  }
+}
+
+from RootDestructuringPattern p, string n, VarDecl v, VarDecl w
 where
-  v = p.getABindingVarRef() and
+  v = p.getFirstClobberedVarDecl(n) and
   w = p.getABindingVarRef() and
-  v.getName() = n and
   w.getName() = n and
-  v != w and
-  v.getLocation().startsBefore(w.getLocation())
+  v != w
 select w, "Repeated binding of pattern variable '" + n + "' previously bound $@.", v, "here"

javascript/ql/test/query-tests/LanguageFeatures/NonLinearPattern/NonLinearPattern.expected

@@ -4,7 +4,6 @@
 | ts-test.ts:21:8:21:13 | string | Repeated binding of pattern variable 'string' previously bound $@. | ts-test.ts:20:8:20:13 | string | here |
 | ts-test.ts:32:16:32:16 | x | Repeated binding of pattern variable 'x' previously bound $@. | ts-test.ts:30:12:30:12 | x | here |
 | ts-test.ts:34:20:34:20 | x | Repeated binding of pattern variable 'x' previously bound $@. | ts-test.ts:30:12:30:12 | x | here |
-| ts-test.ts:34:20:34:20 | x | Repeated binding of pattern variable 'x' previously bound $@. | ts-test.ts:32:16:32:16 | x | here |
 | tst.js:3:13:3:13 | x | Repeated binding of pattern variable 'x' previously bound $@. | tst.js:3:10:3:10 | x | here |
 | tst.js:8:16:8:16 | x | Repeated binding of pattern variable 'x' previously bound $@. | tst.js:8:10:8:10 | x | here |
 | tst.js:11:10:11:10 | x | Repeated binding of pattern variable 'x' previously bound $@. | tst.js:11:7:11:7 | x | here |