Bug 2018245 - Give firefox-devtools-mcp better defaults r=ai4dev-reviewers,padenot

Differential Revision: https://phabricator.services.mozilla.com/D294087

.codex/config.toml

@@ -3,4 +3,4 @@ url = "https://mcp-dev.moz.tools/mcp"
 
 [mcp_servers.firefox-devtools]
 command = "./mach"
-args = ["npx", "@mozilla/firefox-devtools-mcp-moz", "--pref", "browser.ml.enable=true", "--enable-scripting", "--enable-privileged-context"]
+args = ["npx", "@mozilla/firefox-devtools-mcp-moz", "--pref", "browser.ml.enable=true", "--enable-script", "--enable-privileged-context"]

.mcp.json

@@ -9,12 +9,13 @@
       "command": "./mach",
       "args": [
         "--quiet",
-        "npx",
-        "@mozilla/firefox-devtools-mcp-moz",
+        "devtools-mcp",
         "--pref",
-        "browser.ml.enable=true",
-        "--enable-scripting",
-        "--enable-privileged-context"
+        "remote.prefs.recommended=false",
+        "--pref",
+        "browser.smartwindow.enabled=true",
+        "--enable-privileged-context",
+        "--enable-script"
       ]
     }
   }

python/mach/mach/command_util.py

@@ -95,6 +95,7 @@ MACH_COMMANDS = {
     "data-review": MachCommandReference(
         "toolkit/components/glean/build_scripts/mach_commands.py"
     ),
+    "devtools-mcp": MachCommandReference("tools/mach_commands.py"),
     "devtools-node-test": MachCommandReference("devtools/mach_commands.py"),
     "doc": MachCommandReference("tools/moztreedocs/mach_commands.py"),
     "doctor": MachCommandReference("python/mozbuild/mozbuild/mach_commands.py"),

python/mozbuild/mozbuild/test/python.toml

@@ -91,6 +91,8 @@ subsuite = "mozbuild"
 
 ["test_containers.py"]
 
+["test_devtools_mcp.py"]
+
 ["test_dotproperties.py"]
 
 ["test_expression.py"]

python/mozbuild/mozbuild/test/test_devtools_mcp.py

@@ -0,0 +1,161 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import os
+import sys
+import unittest
+from unittest.mock import MagicMock, patch
+
+import buildconfig
+from mach.registrar import Registrar
+from mozunit import main
+
+sys.path.insert(0, os.path.join(buildconfig.topsrcdir, "tools"))
+
+
+class TestDevtoolsMcp(unittest.TestCase):
+    def setUp(self):
+        self.remove_cats = []
+        for cat in ("build", "post-build", "misc", "testing", "devenv"):
+            if cat in Registrar.categories:
+                continue
+            Registrar.register_category(cat, cat, cat)
+            self.remove_cats.append(cat)
+
+    def tearDown(self):
+        for cat in self.remove_cats:
+            del Registrar.categories[cat]
+            del Registrar.commands_by_category[cat]
+
+    def _mock_context(self, topobjdir="/obj", binary_path="/obj/dist/bin/firefox"):
+        ctx = MagicMock()
+        ctx.topobjdir = topobjdir
+        ctx.get_binary_path.return_value = binary_path
+        return ctx
+
+    @patch("os.path.exists", return_value=True)
+    @patch("mach_commands.npx")
+    def test_delegates_to_npx_with_build_args(self, mock_npx, mock_exists):
+        from mach_commands import devtools_mcp
+
+        mock_context = self._mock_context()
+        mock_npx.return_value = 0
+
+        devtools_mcp(mock_context, args=["--pref", "x=1"])
+
+        mock_context.get_binary_path.assert_called_once_with(validate_exists=True)
+        mock_npx.assert_called_once_with(
+            mock_context,
+            [
+                "@mozilla/firefox-devtools-mcp-moz",
+                "--firefox-path",
+                "/obj/dist/bin/firefox",
+                "--profile-path",
+                "/obj/tmp/profile-default",
+                "--pref",
+                "x=1",
+            ],
+        )
+
+    @patch("mach_commands.npx")
+    def test_starts_without_binary_when_no_build(self, mock_npx):
+        from mach_commands import devtools_mcp
+
+        from mozbuild.base import BinaryNotFoundException
+
+        mock_context = self._mock_context()
+        mock_context.get_binary_path.side_effect = BinaryNotFoundException(
+            "/obj/dist/bin/firefox"
+        )
+        mock_npx.return_value = 0
+
+        result = devtools_mcp(mock_context, args=[])
+
+        self.assertEqual(result, 0)
+        mock_npx.assert_called_once_with(
+            mock_context,
+            ["@mozilla/firefox-devtools-mcp-moz"],
+        )
+
+    @patch("mach_commands.npx")
+    def test_starts_without_binary_when_no_build_environment(self, mock_npx):
+        from mach_commands import devtools_mcp
+
+        from mozbuild.base import BuildEnvironmentNotFoundException
+
+        mock_context = self._mock_context()
+        mock_context.get_binary_path.side_effect = BuildEnvironmentNotFoundException(
+            "no build environment"
+        )
+        mock_npx.return_value = 0
+
+        result = devtools_mcp(mock_context, args=[])
+
+        self.assertEqual(result, 0)
+        mock_npx.assert_called_once_with(
+            mock_context,
+            ["@mozilla/firefox-devtools-mcp-moz"],
+        )
+
+    @patch("os.path.exists", return_value=True)
+    @patch("mach_commands.npx")
+    def test_works_with_no_extra_args(self, mock_npx, mock_exists):
+        from mach_commands import devtools_mcp
+
+        mock_context = self._mock_context()
+        mock_npx.return_value = 0
+
+        devtools_mcp(mock_context, args=[])
+
+        mock_npx.assert_called_once_with(
+            mock_context,
+            [
+                "@mozilla/firefox-devtools-mcp-moz",
+                "--firefox-path",
+                "/obj/dist/bin/firefox",
+                "--profile-path",
+                "/obj/tmp/profile-default",
+            ],
+        )
+
+    @patch("os.path.exists", return_value=True)
+    @patch("mach_commands.npx")
+    def test_profile_path_derives_from_topobjdir(self, mock_npx, mock_exists):
+        from mach_commands import devtools_mcp
+
+        mock_context = self._mock_context(
+            topobjdir="/builds/objdir",
+            binary_path="/somewhere/else/dist/bin/firefox",
+        )
+        mock_npx.return_value = 0
+
+        devtools_mcp(mock_context, args=[])
+
+        call_args = mock_npx.call_args[0][1]
+        profile_idx = call_args.index("--profile-path")
+        self.assertEqual(
+            call_args[profile_idx + 1], "/builds/objdir/tmp/profile-default"
+        )
+
+    @patch("os.path.exists", return_value=True)
+    @patch("mach_commands.npx")
+    def test_skips_binary_detection_when_firefox_path_provided(
+        self, mock_npx, mock_exists
+    ):
+        from mach_commands import devtools_mcp
+
+        mock_context = self._mock_context()
+        mock_npx.return_value = 0
+
+        devtools_mcp(mock_context, args=["--firefox-path", "/custom/firefox"])
+
+        mock_context.get_binary_path.assert_not_called()
+        mock_npx.assert_called_once_with(
+            mock_context,
+            ["@mozilla/firefox-devtools-mcp-moz", "--firefox-path", "/custom/firefox"],
+        )
+
+
+if __name__ == "__main__":
+    main()

tools/mach_commands.py

@@ -310,6 +310,41 @@ def npx(command_context, args):
     )
 
 
+@Command(
+    "devtools-mcp",
+    category="devenv",
+    description="Run the firefox-devtools-mcp server with the local build.",
+)
+@CommandArgument("args", nargs=argparse.REMAINDER)
+def devtools_mcp(command_context, args):
+    import os
+    from pathlib import Path
+
+    from mozbuild.base import BinaryNotFoundException, BuildEnvironmentNotFoundException
+
+    extra_args = []
+
+    if "--firefox-path" not in args and "--firefoxPath" not in args:
+        binary_path = None
+        try:
+            binary_path = command_context.get_binary_path(validate_exists=True)
+        except (BuildEnvironmentNotFoundException, BinaryNotFoundException) as e:
+            print(f"Warning: Local build not found: {e}")
+
+        if binary_path and os.path.exists(binary_path):
+            extra_args += ["--firefox-path", binary_path]
+            if "--profile-path" not in args and "--profilePath" not in args:
+                profile_path = (
+                    Path(command_context.topobjdir) / "tmp" / "profile-default"
+                ).as_posix()
+                extra_args += ["--profile-path", profile_path]
+
+    return npx(
+        command_context,
+        ["@mozilla/firefox-devtools-mcp-moz"] + extra_args + args,
+    )
+
+
 def logspam_create_parser(subcommand):
     # Create the logspam command line parser.
     # if logspam is not installed, or not up to date, it will