From 18ba53f84224f76fa140b1af12248b1d43f0e0e3 Mon Sep 17 00:00:00 2001
From: Fabian Meumertzheim <fabian@meumertzhe.im>
Date: Fri, 14 Apr 2023 16:16:51 +0200
Subject: [PATCH] Add `alias_label` struct field to all targets

This allows rules to obtain the label of an `alias` target rather than
only the label of the target an alias chain ultimately resolves to. The
former is the label as specified by the user on the rule, which can be
important to know for e.g. fixup messages and manual implementations of
location expansion.
---
 .../build/lib/analysis/ConfiguredTarget.java  |  3 ++
 .../AbstractConfiguredTarget.java             |  4 +++
 .../lib/rules/AliasConfiguredTarget.java      | 20 ++++++-----
 .../core/TransitiveInfoCollectionApi.java     |  9 ++++-
 .../lib/starlark/StarlarkRuleContextTest.java | 33 +++++++++++++++++++
 5 files changed, 60 insertions(+), 9 deletions(-)

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTarget.java b/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTarget.java
index a53fea14973223..19da56f205364c 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTarget.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTarget.java
@@ -39,6 +39,9 @@ public interface ConfiguredTarget extends TransitiveInfoCollection, Structure {
   /** All <code>ConfiguredTarget</code>s have a "label" field. */
   String LABEL_FIELD = "label";
 
+  /** All <code>ConfiguredTarget</code>s have an "alias_label" field. */
+  String ALIAS_LABEL_FIELD = "alias_label";
+
   /** All <code>ConfiguredTarget</code>s have a "files" field. */
   String FILES_FIELD = "files";
 
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/AbstractConfiguredTarget.java b/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/AbstractConfiguredTarget.java
index 0c3330d0f5586c..8d1515a651d5ab 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/AbstractConfiguredTarget.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/AbstractConfiguredTarget.java
@@ -66,6 +66,7 @@ public abstract class AbstractConfiguredTarget implements ConfiguredTarget, Visi
   // attributed to normal user-specified providers).
   private static final ImmutableSet<String> SPECIAL_FIELD_NAMES =
       ImmutableSet.of(
+          ALIAS_LABEL_FIELD,
           LABEL_FIELD,
           FILES_FIELD,
           DEFAULT_RUNFILES_FIELD,
@@ -141,6 +142,9 @@ public Object getValue(String name) {
     switch (name) {
       case LABEL_FIELD:
         return getLabel();
+      case ALIAS_LABEL_FIELD:
+        // Overridden in AliasConfiguredTarget.
+        return Starlark.NONE;
       case ACTIONS_FIELD_NAME:
         // Depending on subclass, the 'actions' field will either be unsupported or of type
         // java.util.List, which needs to be converted to Sequence before being returned.
diff --git a/src/main/java/com/google/devtools/build/lib/rules/AliasConfiguredTarget.java b/src/main/java/com/google/devtools/build/lib/rules/AliasConfiguredTarget.java
index 14711711471c24..ab4a9033169844 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/AliasConfiguredTarget.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/AliasConfiguredTarget.java
@@ -163,15 +163,19 @@ public BuildConfigurationKey getConfigurationKey() {
 
   @Override
   public Object getValue(String name) {
-    if (name.equals(LABEL_FIELD)) {
-      return getLabel();
-    } else if (name.equals(FILES_FIELD)) {
-      // A shortcut for files to build in Starlark. FileConfiguredTarget and RuleConfiguredTarget
-      // always has FileProvider and Error- and PackageGroupConfiguredTarget-s shouldn't be
-      // accessible in Starlark.
-      return Depset.of(Artifact.class, getProvider(FileProvider.class).getFilesToBuild());
+    switch (name) {
+      case LABEL_FIELD:
+        return getLabel();
+      case ALIAS_LABEL_FIELD:
+        return getOriginalLabel();
+      case FILES_FIELD:
+        // A shortcut for files to build in Starlark. FileConfiguredTarget and RuleConfiguredTarget
+        // always has FileProvider and Error- and PackageGroupConfiguredTarget-s shouldn't be
+        // accessible in Starlark.
+        return Depset.of(Artifact.class, getProvider(FileProvider.class).getFilesToBuild());
+      default:
+        return actual.getValue(name);
     }
-    return actual.getValue(name);
   }
 
   @Override
diff --git a/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/core/TransitiveInfoCollectionApi.java b/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/core/TransitiveInfoCollectionApi.java
index 3b7485c5b79712..ecbe5312405939 100644
--- a/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/core/TransitiveInfoCollectionApi.java
+++ b/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/core/TransitiveInfoCollectionApi.java
@@ -33,7 +33,14 @@
             + "<ul>\n" //
             + "<li><h3 id='modules.Target.label'>label</h3>\n" //
             + "<code><a href='../builtins/Label.html'>Label</a> Target.label</code><br/>\n" //
-            + "The identifier of the target.</li>\n" //
+            + "The label of the target after following all <code><a " //
+            + "href='general.html#alias>alias</a></code>es.</li>\n" //
+            //
+            + "<ul>\n" //
+            + "<li><h3 id='modules.Target.alias_label'>alias_label</h3>\n" //
+            + "<code><a href='../builtins/Label.html'>Label</a> Target.alias_label</code><br/>\n" //
+            + "The label of the target if it is an <code><a" //
+            + "href='general.html#alias>alias</a></code>, otherwise <code>None</code>.</li>\n" //
             //
             + "<li><h3 id='modules.Target.files'>files</h3>\n" //
             + "<code><a href='../builtins/depset.html'>depset</a> Target.files </code><br/>\n" //
diff --git a/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleContextTest.java b/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleContextTest.java
index 4460e5d652e112..3dc2085e4075f1 100644
--- a/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleContextTest.java
+++ b/src/test/java/com/google/devtools/build/lib/starlark/StarlarkRuleContextTest.java
@@ -4062,4 +4062,37 @@ public void testTemplateExpansionComputedSubstitutionMapEachMustBeTopLevel() thr
 
     checkError("//test:testing", "must be declared by a top-level def statement");
   }
+
+  @Test
+  public void testTargetAliasLabel() throws Exception {
+    scratch.file(
+        "test/rules.bzl",
+        "def _my_rule_impl(ctx):",
+        "  direct_dep = ctx.attr.deps[0]",
+        "  direct_dep.label == Label('//test:target') or fail()",
+        "  direct_dep.alias_label == None or fail()",
+        "  alias_dep = ctx.attr.deps[1]",
+        "  alias_dep.label == Label('//test:target') or fail()",
+        "  alias_dep.alias_label == Label('//test:alias') or fail()",
+        "my_rule = rule(",
+        "  implementation = _my_rule_impl,",
+        "  attrs = {'deps': attr.label_list()},",
+        ")");
+    scratch.file(
+        "test/BUILD",
+        "load(':rules.bzl', 'my_rule')",
+        "my_rule(",
+        "    name = 'my_rule',",
+        "    deps = [",
+        "        ':target',",
+        "        ':alias',",
+        "    ],",
+        ")",
+        "",
+        "cc_binary(name = 'target')",
+        "alias(name = 'alias', actual = ':further_alias')",
+        "alias(name = 'further_alias', actual = ':target')");
+
+    getConfiguredTarget("//test:my_rule");
+  }
 }