toolchains: Allow users to provide custom paths to toolchains (#37009)

- **toolchains: Add new state to toolchain selector**
- **Use toolchain term for Add Toolchain button**
- **Hoist out a meta function for toolchain listers**

Closes #27332

Release Notes:

- python: Users can now specify a custom path to their virtual
environment from within the picker.

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

crates/language/src/language.rs

@@ -69,6 +69,7 @@ pub use text_diff::{
 use theme::SyntaxTheme;
 pub use toolchain::{
     LanguageToolchainStore, LocalLanguageToolchainStore, Toolchain, ToolchainList, ToolchainLister,
+    ToolchainMetadata, ToolchainScope,
 };
 use tree_sitter::{self, Query, QueryCursor, WasmStore, wasmtime};
 use util::serde::default_true;

crates/language/src/toolchain.rs

@@ -29,6 +29,40 @@ pub struct Toolchain {
     pub as_json: serde_json::Value,
 }
 
+/// Declares a scope of a toolchain added by user.
+///
+/// When the user adds a toolchain, we give them an option to see that toolchain in:
+/// - All of their projects
+/// - A project they're currently in.
+/// - Only in the subproject they're currently in.
+#[derive(Clone, Debug, Eq, PartialEq, Ord, PartialOrd)]
+pub enum ToolchainScope {
+    Subproject(WorktreeId, Arc<Path>),
+    Project,
+    /// Available in all projects on this box. It wouldn't make sense to show suggestions across machines.
+    Global,
+}
+
+impl ToolchainScope {
+    pub fn label(&self) -> &'static str {
+        match self {
+            ToolchainScope::Subproject(_, _) => "Subproject",
+            ToolchainScope::Project => "Project",
+            ToolchainScope::Global => "Global",
+        }
+    }
+
+    pub fn description(&self) -> &'static str {
+        match self {
+            ToolchainScope::Subproject(_, _) => {
+                "Available only in the subproject you're currently in."
+            }
+            ToolchainScope::Project => "Available in all locations in your current project.",
+            ToolchainScope::Global => "Available in all of your projects on this machine.",
+        }
+    }
+}
+
 impl std::hash::Hash for Toolchain {
     fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
         let Self {
@@ -58,23 +92,41 @@ impl PartialEq for Toolchain {
 }
 
 #[async_trait]
-pub trait ToolchainLister: Send + Sync {
+pub trait ToolchainLister: Send + Sync + 'static {
+    /// List all available toolchains for a given path.
     async fn list(
         &self,
         worktree_root: PathBuf,
         subroot_relative_path: Arc<Path>,
         project_env: Option<HashMap<String, String>>,
     ) -> ToolchainList;
-    // Returns a term which we should use in UI to refer to a toolchain.
-    fn term(&self) -> SharedString;
-    /// Returns the name of the manifest file for this toolchain.
-    fn manifest_name(&self) -> ManifestName;
+
+    /// Given a user-created toolchain, resolve lister-specific details.
+    /// Put another way: fill in the details of the toolchain so the user does not have to.
+    async fn resolve(
+        &self,
+        path: PathBuf,
+        project_env: Option<HashMap<String, String>>,
+    ) -> anyhow::Result<Toolchain>;
+
     async fn activation_script(
         &self,
         toolchain: &Toolchain,
         shell: ShellKind,
         fs: &dyn Fs,
     ) -> Vec<String>;
+    /// Returns various "static" bits of information about this toolchain lister. This function should be pure.
+    fn meta(&self) -> ToolchainMetadata;
+}
+
+#[derive(Clone, PartialEq, Eq, Hash)]
+pub struct ToolchainMetadata {
+    /// Returns a term which we should use in UI to refer to toolchains produced by a given `[ToolchainLister]`.
+    pub term: SharedString,
+    /// A user-facing placeholder describing the semantic meaning of a path to a new toolchain.
+    pub new_toolchain_placeholder: SharedString,
+    /// The name of the manifest file for this toolchain.
+    pub manifest_name: ManifestName,
 }
 
 #[async_trait(?Send)]