Add reaching definition analysis for Optional Chaining

PiperOrigin-RevId: 321995452

Author: rishipal

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

@@ -247,14 +247,11 @@ private void computeMustDef(
       case WHILE:
       case DO:
       case IF:
+      case FOR:
         computeMustDef(
             NodeUtil.getConditionExpression(n), cfgNode, output, conditional);
         return;
 
-      case FOR:
-        computeMustDef(NodeUtil.getConditionExpression(n), cfgNode, output, conditional);
-        return;
-
       case FOR_IN:
       case FOR_OF:
       case FOR_AWAIT_OF:
@@ -278,10 +275,19 @@ private void computeMustDef(
       case AND:
       case OR:
       case COALESCE:
+      case OPTCHAIN_GETPROP:
+      case OPTCHAIN_GETELEM:
         computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
         computeMustDef(n.getLastChild(), cfgNode, output, true);
         return;
 
+      case OPTCHAIN_CALL:
+        computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
+        for (Node c = n.getSecondChild(); c != null; c = c.getNext()) {
+          computeMustDef(c, cfgNode, output, true);
+        }
+        return;
+
       case HOOK:
         computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
         computeMustDef(n.getSecondChild(), cfgNode, output, true);

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

@@ -31,6 +31,8 @@
 /**
  * Tests for {@link MustBeReachingVariableDef}.
  *
+ * <p>Tests in this class look for the labels 'D:' and 'U:' in the input code and check whether the
+ * definition of a var `x` at label `D:` is the must-reaching definition for its use at label `U:`.
  */
 @RunWith(JUnit4.class)
 public final class MustBeReachingVariableDefTest {
@@ -76,14 +78,31 @@ public void testLoops() {
   public void testConditional() {
     assertMatch("var x=0,y; D:(x=1)&&y; U:x");
     assertNotMatch("var x=0,y; D:y&&(x=1); U:x");
+    assertNotMatch("D:var x=0; var y; y&&(x=1); U:x");
   }
 
   @Test
   public void nullishCoalesce() {
-    // LHS is always executed so the definition of  x = 1 must be reached
+    // LHS is always executed so the definition of x = 1 must be reached
     assertMatch("var x=0,y; D:(x=1)??y; U:x");
     // definitions in RHS are not always executed
-    assertNotMatch("var x=0,y; D:y??(x=1); U:x");
+    assertNotMatch("var x=0; var y; D:y??(x=1); U:x");
+    assertNotMatch("D:var x=0; var y; y??(x=1); U:x");
+  }
+
+  @Test
+  public void optionalChaining() {
+    // LHS is always executed so the definition of x = 1 must be reached
+    assertMatch("var x=0,y; D:(x=1)?.y; U:x");
+    assertMatch("var x=0,y; D:(x=1)?.[y]; U:x");
+    assertMatch("var x=0,y; D:(x=1)?.(y); U:x");
+    assertMatch("var x=0,y,z; D:z(x=1)?.y; U:x");
+    assertMatch("var x=0,y,z; D:z[x=1]?.y; U:x");
+
+    // definitions in RHS are not always executed
+    assertNotMatch("var x = 0,y; D:y?.(x=1); U:x");
+    assertNotMatch("D:var x = 0; var y; y?.(x=1); U:x");
+    assertNotMatch("var x=0,y; D:y?.[x=1]; U:x");
   }
 
   @Test