Fix string representations for root objects

Root objects should not expose their absolute paths as they break hermeticity.

PiperOrigin-RevId: 168363549

Author: vladmos

src/main/java/com/google/devtools/build/lib/actions/Root.java

@@ -222,6 +222,11 @@ public String toString() {
 
   @Override
   public void repr(SkylarkPrinter printer) {
+    printer.append(isSourceRoot() ? "<source root>" : "<derived root>");
+  }
+
+  @Override
+  public void reprLegacy(SkylarkPrinter printer) {
     printer.append(toString());
   }
 }

src/test/java/com/google/devtools/build/lib/skylark/SkylarkStringRepresentationsTest.java

@@ -179,6 +179,8 @@ private void generateFilesToTestStrings() throws Exception {
         ")",
         "",
         "def _check_impl(ctx):",
+        "  source_file = ctx.attr.srcs[0].files.to_list()[0]",
+        "  generated_file = ctx.attr.srcs[1].files.to_list()[0]",
         "  objects = {",
         "    'target': ctx.attr.deps[0],",
         "    'alias_target': ctx.attr.deps[1],",
@@ -188,8 +190,10 @@ private void generateFilesToTestStrings() throws Exception {
         "    'rule_ctx': ctx,",
         "    'aspect_ctx': ctx.attr.asp_deps[0][aspect_ctx_provider].ctx,",
         "    'aspect_ctx.rule': ctx.attr.asp_deps[0][aspect_ctx_provider].rule,",
-        "    'source_file': ctx.attr.srcs[0].files.to_list()[0],",
-        "    'generated_file': ctx.attr.srcs[1].files.to_list()[0],",
+        "    'source_file': source_file,",
+        "    'generated_file': generated_file,",
+        "    'source_root': source_file.root,",
+        "    'generated_root': generated_file.root,",
         "  }",
         "  return struct(**prepare_params(objects))",
         "check = rule(",
@@ -334,6 +338,19 @@ public void testStringRepresentations_Files() throws Exception {
     }
   }
 
+  @Test
+  public void testStringRepresentations_Root() throws Exception {
+    setSkylarkSemanticsOptions("--incompatible_descriptive_string_representations=true");
+
+    generateFilesToTestStrings();
+    ConfiguredTarget target = getConfiguredTarget("//test/skylark:check");
+
+    for (String suffix : SUFFIXES) {
+      assertThat(target.get("source_root" + suffix)).isEqualTo("<source root>");
+      assertThat(target.get("generated_root" + suffix)).isEqualTo("<derived root>");
+    }
+  }
+
   @Test
   public void testStringRepresentations_Glob() throws Exception {
     setSkylarkSemanticsOptions("--incompatible_descriptive_string_representations=true");