Update Varifier to only suggest var in builder chains where the factory is on the resulting type

So _don't_ suggest `var` if we have `Foo foo = Bar.builder().build()`.

PiperOrigin-RevId: 817691542

Author: dwoffinden

core/src/main/java/com/google/errorprone/bugpatterns/Varifier.java

@@ -22,6 +22,7 @@
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
 import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+import static com.google.errorprone.util.ASTHelpers.getReceiverType;
 import static com.google.errorprone.util.ASTHelpers.getSymbol;
 import static com.google.errorprone.util.ASTHelpers.getType;
 import static com.google.errorprone.util.ASTHelpers.hasImplicitType;
@@ -104,8 +105,13 @@ && isSameType(getType(newClassTree.getIdentifier()), getType(tree.getType()), st
       return fix(tree);
     }
     // Foo foo = Foo.builder()...build();
+    // (but not Bar bar = Foo.builder()...build())
     if (BUILD_METHOD.matches(initializer, state)
-        && streamReceivers(initializer).anyMatch(t -> BUILDER_FACTORY.matches(t, state))) {
+        && streamReceivers(initializer)
+            .anyMatch(
+                t ->
+                    BUILDER_FACTORY.matches(t, state)
+                        && isSameType(getReceiverType(t), getType(tree.getType()), state))) {
       return fix(tree);
     }
     // Foo foo = Foo.createFoo(..);

core/src/test/java/com/google/errorprone/bugpatterns/VarifierTest.java

@@ -183,6 +183,74 @@ public void t() {
         .doTest();
   }
 
+  @Test
+  public void builderChainGeneric() {
+    refactoringHelper
+        .addInputLines(
+            "Test.java",
+            """
+            import com.google.common.collect.ImmutableList;
+
+            class Test {
+              static class Foo {}
+
+              public void t() {
+                ImmutableList<Foo> foos = ImmutableList.<Foo>builder().add(new Foo()).build();
+              }
+            }
+            """)
+        .addOutputLines(
+            "Test.java",
+            """
+            import com.google.common.collect.ImmutableList;
+
+            class Test {
+              static class Foo {}
+
+              public void t() {
+                var foos = ImmutableList.<Foo>builder().add(new Foo()).build();
+              }
+            }
+            """)
+        .doTest();
+  }
+
+  @Test
+  public void builderChain_typeMismatch() {
+    refactoringHelper
+        .addInputLines(
+            "Test.java",
+            """
+            import com.google.common.collect.ImmutableList;
+
+            class Test {
+              static class Foo {
+                static Builder newBuilder() {
+                  return new Builder();
+                }
+
+                static class Builder {
+                  Builder setX(int x) {
+                    return this;
+                  }
+
+                  Bar build() {
+                    return new Bar();
+                  }
+                }
+              }
+
+              static class Bar {}
+
+              public void t() {
+                Bar bar = Foo.newBuilder().setX(1).build();
+              }
+            }
+            """)
+        .expectUnchanged()
+        .doTest();
+  }
+
   @Test
   public void fromFactoryMethod() {
     refactoringHelper