Visit subtrees of the AST in evaluation order

For instance, it makes more sense to visit the RHS of an assignment
first because this is evaluated first.

This also fixes a bug in the validator, which allowed definitions
like "a = a"

RELNOTES: None
PiperOrigin-RevId: 166709589

2 files changed, 9 insertions, 1 deletions

diff --git a/src/test/java/com/google/devtools/build/lib/syntax/SyntaxTreeVisitorTest.java b/src/test/java/com/google/devtools/build/lib/syntax/SyntaxTreeVisitorTest.java
index 79afdb9703..39f46d03b2 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/SyntaxTreeVisitorTest.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/SyntaxTreeVisitorTest.java
@@ -62,7 +62,7 @@ public class SyntaxTreeVisitorTest {
             "  return h + i.j()");
     IdentVisitor visitor = new IdentVisitor();
     ast.accept(visitor);
-    assertThat(idents).containsExactly("a", "b", "c", "d", "e", "f", "g", "h", "i", "j").inOrder();
+    assertThat(idents).containsExactly("b", "a", "c", "e", "d", "f", "g", "h", "i", "j").inOrder();
     assertThat(params).containsExactly("p1", "p2=4", "**p3").inOrder();
   }
 }
diff --git a/src/test/java/com/google/devtools/build/lib/syntax/ValidationTest.java b/src/test/java/com/google/devtools/build/lib/syntax/ValidationTest.java
index 604c53fe4b..49f5dbb293 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/ValidationTest.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/ValidationTest.java
@@ -105,6 +105,14 @@ public class ValidationTest extends EvaluationTestCase {
   }
 
   @Test
+  public void testDefinitionByItself() throws Exception {
+    checkError("name 'a' is not defined", "a = a");
+    checkError("name 'a' is not defined", "a += a");
+    checkError("name 'a' is not defined", "[[] for a in a]");
+    checkError("name 'a' is not defined", "def f():", "  for a in a: pass");
+  }
+
+  @Test
   public void testLocalValidationEnvironmentsAreSeparated() throws Exception {
     parse("def func1():", "  a = 1", "def func2():", "  a = 'abc'\n");
   }