Fix for array constructor with length is not eliminated

src/com/google/javascript/jscomp/AstAnalyzer.java

@@ -162,6 +162,14 @@ boolean functionCallHasSideEffects(Node callNode) {
       if (assumeKnownBuiltinsArePure && BUILTIN_FUNCTIONS_WITHOUT_SIDEEFFECTS.contains(name)) {
         return false;
       }
+      // Array constructor with a single numeric length argument has no side effects
+      // This handles Array() called without the 'new' keyword
+      if (assumeKnownBuiltinsArePure && "Array".equals(name)) {
+        Node arg = callee.getNext();
+        if (arg != null && arg.isNumber()) {
+          return false;
+        }
+      }
     } else if (callee.isGetProp() || callee.isOptChainGetProp()) {
       if (callNode.hasOneChild()
           && assumeKnownBuiltinsArePure
@@ -523,6 +531,15 @@ boolean constructorCallHasSideEffects(Node newNode) {
     }
 
     Node nameNode = newNode.getFirstChild();
+    if (assumeKnownBuiltinsArePure && nameNode.isName() && "Array".equals(nameNode.getString())) {
+      // Array constructor with a single numeric length argument has no side effects
+      // Array(length) creates an empty array of the given length
+      Node arg = nameNode.getNext();
+      if (arg != null && arg.isNumber()) {
+        return false;
+      }
+    }
+
     return !nameNode.isName()
         || !assumeKnownBuiltinsArePure
         || !CONSTRUCTORS_WITHOUT_SIDE_EFFECTS.contains(nameNode.getString());

test/com/google/javascript/jscomp/AstAnalyzerTest.java

@@ -314,6 +314,10 @@ public static ImmutableList<AnalysisCase> cases() {
           kase().js("new Array").token(NEW).expect(true),
           kase().js("new Array(4)").token(NEW).expect(true),
           kase().js("new Array('a', 'b', 'c')").token(NEW).expect(true),
+          kase().js("Array(10)").token(CALL).expect(false),
+          kase().js("Array(1,2,3)").token(CALL).expect(false),
+          kase().js("Array(10)").token(CALL).assumeBuiltinsPure(false).expect(true),
+          kase().js("Array(1,2,3)").token(CALL).assumeBuiltinsPure(false).expect(true),
           kase().js("new SomeClassINeverHeardOf()").token(NEW).expect(true),
 
           // Getters and setters - object rest and spread

test/com/google/javascript/jscomp/PeepholeRemoveDeadCodeTest.java

@@ -2285,4 +2285,18 @@ public void testSwitchCase() {
         "function f() { switch(x) { default: return; case 1: return 5;bar()}}",
         "function f() { switch(x) { default: return; case 1: return 5;}}");
   }
+
+  @Test
+  public void testArrayConstructor() {
+    // Array constructor with length argument only should be eliminated when unused
+    fold("Array(10)", "");
+    fold("Array(5)", "");
+
+    // Array constructor with elements should also be eliminated
+    fold("Array(1,2,3)", "");
+
+    // Array constructor used in expression with side effects
+    fold("Array(10).push(5)", "Array(10).push(5)"); // push has side effects
+    fold("Array(10)[0] = 2", "Array(10)[0] = 2"); // assignment has side effects
+  }
 }