Mark (bigint|number).toString(radix) nosideeffects (fixes #4169)

 - Object.toString() was marked nosideeffects in AstAnalyzer through a
   special code path.
 - We extend this to (number|bigint).toString(radix) as well.

Author: mnsaglam

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

@@ -163,9 +163,9 @@ boolean functionCallHasSideEffects(Node callNode) {
         return false;
       }
     } else if (callee.isGetProp() || callee.isOptChainGetProp()) {
-      if (callNode.hasOneChild()
-          && assumeKnownBuiltinsArePure
-          && OBJECT_METHODS_WITHOUT_SIDEEFFECTS.contains(callee.getString())) {
+      if (assumeKnownBuiltinsArePure
+          && OBJECT_METHODS_WITHOUT_SIDEEFFECTS.contains(callee.getString())
+          && (callNode.hasOneChild() || isNumericToStringCall(callee))) {
         return false;
       }
 
@@ -277,6 +277,32 @@ private boolean isTypedAsString(Node n) {
     return false;
   }
 
+  private boolean isNumericToStringCall(Node callee) {
+    return (callee.isGetProp() || callee.isOptChainGetProp())
+        && "toString".equals(callee.getString())
+        && isTypedAsNumberOrBigInt(callee.getFirstChild());
+  }
+
+  private boolean isTypedAsNumberOrBigInt(Node n) {
+    if (n.isNumber() || n.isBigInt()) {
+      return true;
+    }
+    if (useTypesForLocalOptimization) {
+      Color color = n.getColor();
+      if (color != null) {
+        return color.equals(StandardColors.NUMBER) || color.equals(StandardColors.BIGINT);
+      }
+      JSType type = n.getJSType();
+      if (type != null) {
+        return type.isNumberValueType()
+            || type.isNumberObjectType()
+            || type.isBigIntValueType()
+            || type.isBigIntObjectType();
+      }
+    }
+    return false;
+  }
+
   /**
    * Returns true if some node in n's subtree changes application state. If {@code
    * checkForNewObjects} is true, we assume that newly created mutable objects (like object

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

@@ -657,10 +657,18 @@ public static ImmutableList<AnalysisCase> cases() {
           // IObject methods
           // "toString" and "valueOf" are by default assumed to be side-effect free
           kase().expect(false).js("o.toString()"),
+          kase().expect(false).js("(0).toString(16)"),
+          kase().expect(false).js("(0n).toString(16)"),
+          kase().expect(false).js("(0)?.toString(16)"),
+          kase().expect(false).js("(0n)?.toString(16)"),
           kase().expect(false).js("o.valueOf()"),
           // "toString" and "valueOf" are not assumed to be side-effect free when
           // assumeKnownBuiltinsArePure is false.
           kase().expect(true).js("o.toString()").assumeBuiltinsPure(false),
+          kase().expect(true).js("(0).toString(16)").assumeBuiltinsPure(false),
+          kase().expect(true).js("(0n).toString(16)").assumeBuiltinsPure(false),
+          kase().expect(true).js("(0)?.toString(16)").assumeBuiltinsPure(false),
+          kase().expect(true).js("(0n)?.toString(16)").assumeBuiltinsPure(false),
           kase().expect(true).js("o.valueOf()").assumeBuiltinsPure(false),
           // other methods depend on the extern definitions
           kase().expect(true).js("o.watch()"),

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

@@ -452,4 +452,14 @@ public void testIgnoresRuntimeLibRequireStatementsOnly() {
         srcs(SourceFile.fromCode("other/file.js", "'require base'")),
         warning(CheckSideEffects.USELESS_CODE_ERROR));
   }
+
+  @Test
+  public void testNumberToStringWithRadixIsUselessCode() {
+    testWarning("(0).toString(16);", e);
+  }
+
+  @Test
+  public void testOptionalChainNumberToStringWithRadixIsUselessCode() {
+    testWarning("(0)?.toString(16);", e);
+  }
 }

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

@@ -3668,6 +3668,16 @@ public void testCallCache_propagatesSideEffects() {
         });
   }
 
+  @Test
+  public void testNumberToStringWithRadixIsPure() {
+    assertPureCallsMarked("var x = 0; x.toString(16);", ImmutableList.of("x.toString"));
+  }
+
+  @Test
+  public void testOptionalChainNumberToStringWithRadixIsPure() {
+    assertPureCallsMarked("var x = 0; x?.toString(16);", ImmutableList.of("x?.toString"));
+  }
+
   @Test
   public void testDynamicImport() {
     ignoreWarnings(DiagnosticGroups.MODULE_LOAD);