Scala: answer Metals' build-import prompt

CHANGELOG.md

@@ -33,6 +33,13 @@ Status of the `main` branch. Changes prior to the next official version change w
   - Language servers and their dependency providers now go through the `subprocess_run` helper instead of
     calling `subprocess.run` directly (e.g. for installation processes), so all such subprocesses get 
     `stdin=DEVNULL` and can no longer interfere with the stdio MCP connection #1748
+  - `scala`: Fix: Metals asks via `window/showMessageRequest` whether to import a workspace it has not
+    seen before, and Serena had no handler, so the request failed with `MethodNotFound` and Metals gave
+    up on the import ("Unexpected error initializing server"). No build server was ever connected and
+    every cross-file query fell back to the presentation compiler, which sees one file at a time, unless
+    the project happened to have been imported beforehand by another editor. The three prompts that lead
+    to a build server are now answered; anything else is dismissed, including the choice between several
+    build definitions in one workspace. `ls_specific_settings.scala.auto_import_build: false` opts out
 
 * Hooks:
   - Add `serena-hooks --client=grok`, including Grok-native PreToolUse allow/deny output.

docs/01-about/020_programming-languages.md

@@ -146,7 +146,7 @@ Some languages require additional installations or setup steps, as noted.
 * **Rust**  
   (requires [rustup](https://rustup.rs/) - uses rust-analyzer from your toolchain)
 * **Scala**  
-  (requires some [manual setup](../03-special-guides/scala_setup_guide_for_serena); uses Metals LSP)
+  (uses Metals LSP, which imports the build on first use — see the [setup guide](../03-special-guides/scala_setup_guide_for_serena))
 * **SCSS / Sass / CSS**
   (experimental; requires Node.js + npm; uses [some-sass-language-server](https://github.com/wkillerud/some-sass) to handle
   `.scss`, `.sass`, and `.css`)

docs/03-special-guides/scala_setup_guide_for_serena.md

@@ -15,7 +15,16 @@ Install the following on your system and ensure they are available on `PATH`:
   - Serena uses `cs` if available; if only `coursier` exists, it will attempt to install `cs`. If neither is present, install Coursier first.
 
 ---
-## Quick Start (Recommended: VS Code + Metals auto‑import)
+## Quick Start
+
+Start Serena in your project root. Metals asks whether to import a workspace it has not seen before, and Serena answers that prompt for it — the build is imported (for sbt, by running `sbt bloopInstall`), `.bloop/` and `.metals/` are created, and cross-file navigation works from there. The first run therefore takes as long as your build takes to load.
+
+Set `auto_import_build: false` under `ls_specific_settings.scala` to decline instead; you then need to import the build yourself by one of the routes below, or cross-file queries will be served by the fallback presentation compiler and see only one file at a time.
+
+Serena answers three of Metals' prompts — “Import build”, “Import changes”, “Connect”. Anything else Metals asks is dismissed and logged, including “Multiple build definitions found. Which would you like to use?”, so a workspace holding more than one kind of build (say both an sbt and a Maven definition) still needs importing by one of the routes below.
+
+---
+## Importing the build yourself (VS Code)
 
 1. Open your Scala project in VS Code.
 2. When prompted by Metals, accept “Import build”. Wait until the import and initial compile/indexing finish.
@@ -25,7 +34,7 @@ Install the following on your system and ensure they are available on `PATH`:
 This flow ensures the `.bloop/` and (if applicable) `.metals/` directories are created and your build is known to the build server that Metals uses.
 
 ---
-## Manual Setup (No VS Code)
+## Importing the build yourself (No VS Code)
 
 Follow these steps if you prefer a manual setup or you are not using VS Code:
 

src/solidlsp/language_servers/scala_language_server.py

@@ -28,6 +28,22 @@
 DEFAULT_CLIENT_NAME = "Serena"
 DEFAULT_ON_STALE_LOCK = "auto-clean"
 DEFAULT_LOG_MULTI_INSTANCE_NOTICE = True
+DEFAULT_AUTO_IMPORT_BUILD = True
+
+# The `window/showMessageRequest` actions Serena answers affirmatively: the ones standing between
+# an un-imported workspace and a build server. Everything else is dismissed, since a prompt we do
+# not recognise is one whose consequences we cannot judge — `Messages.OldBloopVersionRunning`
+# offers to kill a process, `Messages.NewScalaProject` to open a window. "Don't show again" is
+# never chosen: Metals persists that dismissal in the project's own state.
+# (scala/meta/internal/metals/Messages.scala, at `ImportBuild`, `ImportBuildChanges`,
+# `GenerateBspAndConnect`.)
+#
+# Not answered, deliberately: `Messages.ChooseBuildTool` ("Multiple build definitions found. Which
+# would you like to use?"), whose actions are the build tools' own executable names. It precedes
+# the import prompt in a workspace holding more than one kind of build, so such a workspace is
+# still not imported — but choosing a build tool for the user is a guess of a different order, and
+# Metals offers no way to say "whichever you would have picked".
+BUILD_IMPORT_PROMPT_ACTIONS = ("Import build", "Import changes", "Connect")
 
 
 class StaleLockMode(Enum):
@@ -43,6 +59,28 @@ class StaleLockMode(Enum):
     """Raise an error and refuse to start."""
 
 
+def choose_show_message_request_action(params: dict, auto_import_build: bool = DEFAULT_AUTO_IMPORT_BUILD) -> dict | None:
+    """
+    Choose Serena's answer to a `window/showMessageRequest`, which Metals uses to ask whether to
+    import the build.
+
+    :param params: the request's `ShowMessageRequestParams`
+    :param auto_import_build: whether to answer the build-import prompts affirmatively
+    :return: the action to select, or None to select none — which is what the LSP spec provides
+        for, and what leaving the request unanswered fails to say
+    """
+    message = params.get("message", "")
+    actions = params.get("actions") or []
+    if auto_import_build:
+        for action in actions:
+            if isinstance(action, dict) and action.get("title") in BUILD_IMPORT_PROMPT_ACTIONS:
+                log.info(f"Metals asked: {message!r}; answering {action['title']!r}")
+                return action
+    offered = [action.get("title") for action in actions if isinstance(action, dict)]
+    log.info(f"Metals asked: {message!r}; dismissing (offered: {offered})")
+    return None
+
+
 def _get_scala_settings(solidlsp_settings: SolidLSPSettings) -> dict[str, object]:
     """
     Extract Scala-specific settings with defaults applied.
@@ -52,6 +90,7 @@ def _get_scala_settings(solidlsp_settings: SolidLSPSettings) -> dict[str, object
         - client_name: str
         - on_stale_lock: StaleLockMode
         - log_multi_instance_notice: bool
+        - auto_import_build: bool
     """
     from solidlsp.ls_config import LanguageServerId
 
@@ -60,6 +99,7 @@ def _get_scala_settings(solidlsp_settings: SolidLSPSettings) -> dict[str, object
         "client_name": DEFAULT_CLIENT_NAME,
         "on_stale_lock": StaleLockMode.AUTO_CLEAN,
         "log_multi_instance_notice": DEFAULT_LOG_MULTI_INSTANCE_NOTICE,
+        "auto_import_build": DEFAULT_AUTO_IMPORT_BUILD,
     }
 
     if not solidlsp_settings.ls_specific_settings:
@@ -80,6 +120,7 @@ def _get_scala_settings(solidlsp_settings: SolidLSPSettings) -> dict[str, object
         "client_name": scala_settings.get("client_name", DEFAULT_CLIENT_NAME),
         "on_stale_lock": on_stale_lock,
         "log_multi_instance_notice": scala_settings.get("log_multi_instance_notice", DEFAULT_LOG_MULTI_INSTANCE_NOTICE),
+        "auto_import_build": scala_settings.get("auto_import_build", DEFAULT_AUTO_IMPORT_BUILD),
     }
 
 
@@ -100,6 +141,14 @@ class ScalaLanguageServer(SolidLanguageServer):
             metals_version: '1.6.4'
             # Client identifier sent to Metals (default: DEFAULT_CLIENT_NAME)
             client_name: 'Serena'
+            # Answer Metals' build-import prompts affirmatively, which lets it run the project's
+            # build tool (e.g. sbt bloopInstall). Set false to leave the build un-imported.
+            auto_import_build: true
+
+    Build import:
+        Metals asks, via `window/showMessageRequest`, whether to import a workspace it has not
+        seen before; until that is answered it has no build server and so no build target, and
+        every cross-file query is served by the fallback presentation compiler.
 
     Multi-instance support:
         Metals uses H2 AUTO_SERVER mode (enabled by default) to support multiple
@@ -116,6 +165,8 @@ def __init__(self, config: LanguageServerConfig, repository_root_path: str, soli
         # Check for stale locks before setting up dependencies (fail-fast)
         self._check_metals_db_status(repository_root_path, solidlsp_settings)
 
+        self._auto_import_build: bool = _get_scala_settings(solidlsp_settings)["auto_import_build"]  # type: ignore[assignment]
+
         scala_lsp_executable_path = self._setup_runtime_dependencies(config, solidlsp_settings)
         super().__init__(
             config,
@@ -300,10 +351,15 @@ def _create_base_initialize_params(self) -> dict:
         }
         return initialize_params
 
+    def _answer_show_message_request(self, params: dict) -> dict | None:
+        return choose_show_message_request_action(params, auto_import_build=self._auto_import_build)
+
     def _start_server(self) -> None:
         """
         Starts the Scala Language Server
         """
+        self.server.on_request("window/showMessageRequest", self._answer_show_message_request)
+
         log.info("Starting Scala server process")
         self.server.start()
 

test/solidlsp/scala/test_scala_show_message_request.py

@@ -0,0 +1,94 @@
+"""
+Unit tests for Serena's answer to Metals' `window/showMessageRequest` prompts.
+"""
+
+import pytest
+
+from solidlsp.language_servers.scala_language_server import (
+    _get_scala_settings,
+    choose_show_message_request_action,
+)
+from solidlsp.ls_config import LanguageServerId
+from solidlsp.settings import SolidLSPSettings
+
+# Metals' own prompts, with the message and action titles as its `Messages` object builds them
+# (scala/meta/internal/metals/Messages.scala) and `type` as lsp4j serialises `MessageType.Info`.
+IMPORT_BUILD = {
+    "message": "New sbt workspace detected, would you like to import the build?",
+    "type": 3,
+    "actions": [{"title": "Import build"}, {"title": "Not now"}, {"title": "Don't show again"}],
+}
+IMPORT_CHANGES = {
+    "message": "sbt build needs to be re-imported",
+    "type": 3,
+    "actions": [{"title": "Import changes"}, {"title": "Not now"}, {"title": "Don't show again"}],
+}
+GENERATE_BSP_AND_CONNECT = {
+    "message": "New sbt workspace detected, would you like connect to the Bloop build server?",
+    "type": 3,
+    "actions": [{"title": "Connect"}, {"title": "Not now"}, {"title": "Don't show again"}],
+}
+OLD_BLOOP_VERSION_RUNNING = {
+    "message": "Deprecated Bloop server is still running and is taking up resources, do you want to kill the process?",
+    "type": 3,
+    "actions": [{"title": "Yes"}, {"title": "Not now"}],
+}
+CHOOSE_BUILD_TOOL = {
+    "message": "Multiple build definitions found. Which would you like to use?",
+    "type": 3,
+    "actions": [{"title": "sbt"}, {"title": "mill"}],
+}
+
+
+@pytest.mark.scala
+class TestChooseShowMessageRequestAction:
+    @pytest.mark.parametrize("params", [IMPORT_BUILD, IMPORT_CHANGES, GENERATE_BSP_AND_CONNECT])
+    def test_build_import_prompts_are_answered_affirmatively(self, params: dict) -> None:
+        chosen = choose_show_message_request_action(params)
+        assert chosen is not None
+        assert chosen["title"] in ("Import build", "Import changes", "Connect")
+
+    @pytest.mark.parametrize("params", [IMPORT_BUILD, IMPORT_CHANGES, GENERATE_BSP_AND_CONNECT])
+    def test_auto_import_build_can_be_turned_off(self, params: dict) -> None:
+        assert choose_show_message_request_action(params, auto_import_build=False) is None
+
+    def test_dont_show_again_is_never_chosen(self) -> None:
+        """Metals persists that dismissal in the project's own state."""
+        params = {"message": "…", "actions": [{"title": "Don't show again"}, {"title": "Not now"}]}
+        assert choose_show_message_request_action(params) is None
+
+    def test_an_unrecognised_prompt_is_dismissed(self) -> None:
+        """Answering "Yes" here would kill a process on the user's machine."""
+        assert choose_show_message_request_action(OLD_BLOOP_VERSION_RUNNING) is None
+
+    def test_a_prompt_with_no_actions_is_dismissed(self) -> None:
+        assert choose_show_message_request_action({"message": "just so you know"}) is None
+        assert choose_show_message_request_action({"message": "just so you know", "actions": None}) is None
+
+    def test_malformed_actions_do_not_raise(self) -> None:
+        params = {"message": "…", "actions": ["Import build", None, {"title": "Import build"}]}
+        assert choose_show_message_request_action(params) == {"title": "Import build"}
+
+    def test_choosing_between_build_tools_is_left_alone(self) -> None:
+        """Naming the build tool for the user is a guess of a different order; see the comment
+        on BUILD_IMPORT_PROMPT_ACTIONS. A workspace with several build definitions is therefore
+        still not imported.
+        """
+        assert choose_show_message_request_action(CHOOSE_BUILD_TOOL) is None
+
+
+@pytest.mark.scala
+class TestAutoImportBuildSetting:
+    """`auto_import_build` has to reach the handler from the project configuration."""
+
+    @staticmethod
+    def setting(**scala_settings) -> object:
+        settings = SolidLSPSettings(ls_specific_settings={LanguageServerId.SCALA: scala_settings})
+        return _get_scala_settings(settings)["auto_import_build"]
+
+    def test_defaults_to_true(self) -> None:
+        assert self.setting() is True
+        assert _get_scala_settings(SolidLSPSettings())["auto_import_build"] is True
+
+    def test_can_be_disabled(self) -> None:
+        assert self.setting(auto_import_build=False) is False