From 645d471e2a7c78d9cb5c22b6de4558966f8bae6a Mon Sep 17 00:00:00 2001
From: salma-samy <salmasamy@google.com>
Date: Fri, 16 Feb 2024 02:25:54 -0800
Subject: [PATCH] Mod command fails if bzlmod is disabled (fixes: #21303)

PiperOrigin-RevId: 607621058
Change-Id: Id58e92d4f80e408e5bf4deabe08e8a864940de63
---
 .../build/lib/bazel/commands/ModCommand.java  | 21 +++++++------------
 .../devtools/build/lib/bazel/commands/mod.txt |  1 +
 src/test/py/bazel/bzlmod/mod_command_test.py  | 10 +++++++++
 3 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/src/main/java/com/google/devtools/build/lib/bazel/commands/ModCommand.java b/src/main/java/com/google/devtools/build/lib/bazel/commands/ModCommand.java
index 611764b553e274..ec08bfafd50d55 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/commands/ModCommand.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/commands/ModCommand.java
@@ -56,6 +56,7 @@
 import com.google.devtools.build.lib.cmdline.RepositoryMapping;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
 import com.google.devtools.build.lib.events.Event;
+import com.google.devtools.build.lib.packages.semantics.BuildLanguageOptions;
 import com.google.devtools.build.lib.pkgcache.PackageOptions;
 import com.google.devtools.build.lib.runtime.BlazeCommand;
 import com.google.devtools.build.lib.runtime.BlazeCommandResult;
@@ -82,8 +83,6 @@
 import com.google.devtools.build.skyframe.SkyFunctionException;
 import com.google.devtools.build.skyframe.SkyKey;
 import com.google.devtools.build.skyframe.SkyValue;
-import com.google.devtools.common.options.OptionPriority.PriorityCategory;
-import com.google.devtools.common.options.OptionsParser;
 import com.google.devtools.common.options.OptionsParsingException;
 import com.google.devtools.common.options.OptionsParsingResult;
 import com.google.gson.Gson;
@@ -120,20 +119,14 @@ public final class ModCommand implements BlazeCommand {
   public static final String NAME = "mod";
 
   @Override
-  public void editOptions(OptionsParser optionsParser) {
-    try {
-      optionsParser.parse(
-          PriorityCategory.SOFTWARE_REQUIREMENT,
-          "Option required by the mod command",
-          ImmutableList.of("--enable_bzlmod"));
-    } catch (OptionsParsingException e) {
-      // Should never happen.
-      throw new IllegalStateException("Unexpected exception", e);
+  public BlazeCommandResult exec(CommandEnvironment env, OptionsParsingResult options) {
+    if (!options.getOptions(BuildLanguageOptions.class).enableBzlmod) {
+      return reportAndCreateFailureResult(
+          env,
+          "Bzlmod has to be enabled for mod command to work, run with --enable_bzlmod",
+          Code.MISSING_ARGUMENTS);
     }
-  }
 
-  @Override
-  public BlazeCommandResult exec(CommandEnvironment env, OptionsParsingResult options) {
     env.getEventBus()
         .post(
             new NoBuildEvent(
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/commands/mod.txt b/src/main/java/com/google/devtools/build/lib/bazel/commands/mod.txt
index efd63df44df19b..f81995a286db83 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/commands/mod.txt
+++ b/src/main/java/com/google/devtools/build/lib/bazel/commands/mod.txt
@@ -2,6 +2,7 @@
 Usage: %{product} %{command} [<option> ...] tidy|<query_type> [<args> ...]
 
 When invoked as %{product} %{command} tidy, the command will format the MODULE.bazel file and update all use_repo calls for supported module extensions.
+Only works when bzlmod is enabled via --enable_bzlmod.
 
 The command will display the external dependency graph or parts thereof, structured to display different kinds of insights depending on the query type.
 
diff --git a/src/test/py/bazel/bzlmod/mod_command_test.py b/src/test/py/bazel/bzlmod/mod_command_test.py
index 40e850ddb39b18..cc78dbad5f54c2 100644
--- a/src/test/py/bazel/bzlmod/mod_command_test.py
+++ b/src/test/py/bazel/bzlmod/mod_command_test.py
@@ -133,6 +133,16 @@ def setUp(self):
     scratchFile(self.projects_dir.joinpath('ext2', 'BUILD'))
     scratchFile(self.projects_dir.joinpath('ext2', 'ext.bzl'), ext_src)
 
+  def testFailWithoutBzlmod(self):
+    _, _, stderr = self.RunBazel(
+        ['mod', 'graph', '--noenable_bzlmod'], allow_failure=True
+    )
+    self.assertIn(
+        'ERROR: Bzlmod has to be enabled for mod command to work, run with '
+        "--enable_bzlmod. Type 'bazel help mod' for syntax and help.",
+        stderr,
+    )
+
   def testGraph(self):
     _, stdout, _ = self.RunBazel(['mod', 'graph'], rstrip=True)
     self.assertListEqual(