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/language/src/language.rs

@@ -15,6 +15,7 @@ mod outline;
 pub mod proto;
 mod syntax_map;
 mod task_context;
+mod toolchain;
 
 #[cfg(test)]
 pub mod buffer_tests;
@@ -28,7 +29,7 @@ use futures::Future;
 use gpui::{AppContext, AsyncAppContext, Model, SharedString, Task};
 pub use highlight_map::HighlightMap;
 use http_client::HttpClient;
-pub use language_registry::LanguageName;
+pub use language_registry::{LanguageName, LoadedLanguage};
 use lsp::{CodeActionKind, LanguageServerBinary, LanguageServerBinaryOptions};
 use parking_lot::Mutex;
 use regex::Regex;
@@ -61,6 +62,7 @@ use syntax_map::{QueryCursorHandle, SyntaxSnapshot};
 use task::RunnableTag;
 pub use task_context::{ContextProvider, RunnableRange};
 use theme::SyntaxTheme;
+pub use toolchain::{LanguageToolchainStore, Toolchain, ToolchainList, ToolchainLister};
 use tree_sitter::{self, wasmtime, Query, QueryCursor, WasmStore};
 use util::serde::default_true;
 
@@ -502,6 +504,7 @@ pub trait LspAdapter: 'static + Send + Sync {
     async fn workspace_configuration(
         self: Arc<Self>,
         _: &Arc<dyn LspAdapterDelegate>,
+        _: Arc<dyn LanguageToolchainStore>,
         _cx: &mut AsyncAppContext,
     ) -> Result<Value> {
         Ok(serde_json::json!({}))
@@ -855,6 +858,7 @@ pub struct Language {
     pub(crate) config: LanguageConfig,
     pub(crate) grammar: Option<Arc<Grammar>>,
     pub(crate) context_provider: Option<Arc<dyn ContextProvider>>,
+    pub(crate) toolchain: Option<Arc<dyn ToolchainLister>>,
 }
 
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy)]
@@ -983,6 +987,7 @@ impl Language {
                 })
             }),
             context_provider: None,
+            toolchain: None,
         }
     }
 
@@ -991,6 +996,11 @@ impl Language {
         self
     }
 
+    pub fn with_toolchain_lister(mut self, provider: Option<Arc<dyn ToolchainLister>>) -> Self {
+        self.toolchain = provider;
+        self
+    }
+
     pub fn with_queries(mut self, queries: LanguageQueries) -> Result<Self> {
         if let Some(query) = queries.highlights {
             self = self
@@ -1361,6 +1371,10 @@ impl Language {
         self.context_provider.clone()
     }
 
+    pub fn toolchain_lister(&self) -> Option<Arc<dyn ToolchainLister>> {
+        self.toolchain.clone()
+    }
+
     pub fn highlight_text<'a>(
         self: &'a Arc<Self>,
         text: &'a Rope,