Add language toolchains (#19576)

This PR adds support for selecting toolchains for a given language (e.g.
Rust toolchains or Python virtual environments) with support for SSH
projects provided out of the box. For Python we piggy-back off of
[PET](https://github.com/microsoft/python-environment-tools), a library
maintained by Microsoft.
Closes #16421
Closes #7646

Release Notes:

- Added toolchain selector to the status bar (with initial support for
Python virtual environments)

crates/extension/src/extension_lsp_adapter.rs

@@ -8,7 +8,8 @@ use collections::HashMap;
 use futures::{Future, FutureExt};
 use gpui::AsyncAppContext;
 use language::{
-    CodeLabel, HighlightId, Language, LanguageServerName, LspAdapter, LspAdapterDelegate,
+    CodeLabel, HighlightId, Language, LanguageServerName, LanguageToolchainStore, LspAdapter,
+    LspAdapterDelegate,
 };
 use lsp::{CodeActionKind, LanguageServerBinary, LanguageServerBinaryOptions};
 use serde::Serialize;
@@ -194,6 +195,7 @@ impl LspAdapter for ExtensionLspAdapter {
     async fn workspace_configuration(
         self: Arc<Self>,
         delegate: &Arc<dyn LspAdapterDelegate>,
+        _: Arc<dyn LanguageToolchainStore>,
         _cx: &mut AsyncAppContext,
     ) -> Result<Value> {
         let delegate = delegate.clone();

crates/extension/src/extension_store.rs

@@ -37,7 +37,7 @@ use http_client::{AsyncBody, HttpClient, HttpClientWithUrl};
 use indexed_docs::{IndexedDocsRegistry, ProviderId};
 use language::{
     LanguageConfig, LanguageMatcher, LanguageName, LanguageQueries, LanguageRegistry,
-    QUERY_FILENAME_PREFIXES,
+    LoadedLanguage, QUERY_FILENAME_PREFIXES,
 };
 use node_runtime::NodeRuntime;
 use project::ContextProviderWithTasks;
@@ -1102,14 +1102,21 @@ impl ExtensionStore {
                     let config = std::fs::read_to_string(language_path.join("config.toml"))?;
                     let config: LanguageConfig = ::toml::from_str(&config)?;
                     let queries = load_plugin_queries(&language_path);
-                    let tasks = std::fs::read_to_string(language_path.join("tasks.json"))
-                        .ok()
-                        .and_then(|contents| {
-                            let definitions = serde_json_lenient::from_str(&contents).log_err()?;
-                            Some(Arc::new(ContextProviderWithTasks::new(definitions)) as Arc<_>)
-                        });
+                    let context_provider =
+                        std::fs::read_to_string(language_path.join("tasks.json"))
+                            .ok()
+                            .and_then(|contents| {
+                                let definitions =
+                                    serde_json_lenient::from_str(&contents).log_err()?;
+                                Some(Arc::new(ContextProviderWithTasks::new(definitions)) as Arc<_>)
+                            });
 
-                    Ok((config, queries, tasks))
+                    Ok(LoadedLanguage {
+                        config,
+                        queries,
+                        context_provider,
+                        toolchain_provider: None,
+                    })
                 },
             );
         }