Add new extension crate (#20089)

This PR adds a new `extension` crate, containing some contents extracted
from the `extension_host`.

Right now it contains just the `ExtensionManifest` and
`ExtensionBuilder`, although we may move more of the extension interface
into here.

The introduction of the `extension` crate allows us to depend on it in
the `extension_cli`, thereby eliminating the need for the `no-webrtc`
feature on a number of crates.

Release Notes:

- N/A

crates/extension/src/extension_manifest.rs

@@ -0,0 +1,212 @@
+use anyhow::{anyhow, Context, Result};
+use collections::{BTreeMap, HashMap};
+use fs::Fs;
+use language::{LanguageName, LanguageServerName};
+use semantic_version::SemanticVersion;
+use serde::{Deserialize, Serialize};
+use std::{
+    ffi::OsStr,
+    fmt,
+    path::{Path, PathBuf},
+    sync::Arc,
+};
+
+/// This is the old version of the extension manifest, from when it was `extension.json`.
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
+pub struct OldExtensionManifest {
+    pub name: String,
+    pub version: Arc<str>,
+
+    #[serde(default)]
+    pub description: Option<String>,
+    #[serde(default)]
+    pub repository: Option<String>,
+    #[serde(default)]
+    pub authors: Vec<String>,
+
+    #[serde(default)]
+    pub themes: BTreeMap<Arc<str>, PathBuf>,
+    #[serde(default)]
+    pub languages: BTreeMap<Arc<str>, PathBuf>,
+    #[serde(default)]
+    pub grammars: BTreeMap<Arc<str>, PathBuf>,
+}
+
+/// The schema version of the [`ExtensionManifest`].
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy, Serialize, Deserialize)]
+pub struct SchemaVersion(pub i32);
+
+impl fmt::Display for SchemaVersion {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl SchemaVersion {
+    pub const ZERO: Self = Self(0);
+
+    pub fn is_v0(&self) -> bool {
+        self == &Self::ZERO
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
+pub struct ExtensionManifest {
+    pub id: Arc<str>,
+    pub name: String,
+    pub version: Arc<str>,
+    pub schema_version: SchemaVersion,
+
+    #[serde(default)]
+    pub description: Option<String>,
+    #[serde(default)]
+    pub repository: Option<String>,
+    #[serde(default)]
+    pub authors: Vec<String>,
+    #[serde(default)]
+    pub lib: LibManifestEntry,
+
+    #[serde(default)]
+    pub themes: Vec<PathBuf>,
+    #[serde(default)]
+    pub languages: Vec<PathBuf>,
+    #[serde(default)]
+    pub grammars: BTreeMap<Arc<str>, GrammarManifestEntry>,
+    #[serde(default)]
+    pub language_servers: BTreeMap<LanguageServerName, LanguageServerManifestEntry>,
+    #[serde(default)]
+    pub slash_commands: BTreeMap<Arc<str>, SlashCommandManifestEntry>,
+    #[serde(default)]
+    pub indexed_docs_providers: BTreeMap<Arc<str>, IndexedDocsProviderEntry>,
+    #[serde(default)]
+    pub snippets: Option<PathBuf>,
+}
+
+#[derive(Clone, Default, PartialEq, Eq, Debug, Deserialize, Serialize)]
+pub struct LibManifestEntry {
+    pub kind: Option<ExtensionLibraryKind>,
+    pub version: Option<SemanticVersion>,
+}
+
+#[derive(Clone, PartialEq, Eq, Debug, Deserialize, Serialize)]
+pub enum ExtensionLibraryKind {
+    Rust,
+}
+
+#[derive(Clone, Default, PartialEq, Eq, Debug, Deserialize, Serialize)]
+pub struct GrammarManifestEntry {
+    pub repository: String,
+    #[serde(alias = "commit")]
+    pub rev: String,
+    #[serde(default)]
+    pub path: Option<String>,
+}
+
+#[derive(Clone, PartialEq, Eq, Debug, Deserialize, Serialize)]
+pub struct LanguageServerManifestEntry {
+    /// Deprecated in favor of `languages`.
+    #[serde(default)]
+    language: Option<LanguageName>,
+    /// The list of languages this language server should work with.
+    #[serde(default)]
+    languages: Vec<LanguageName>,
+    #[serde(default)]
+    pub language_ids: HashMap<String, String>,
+    #[serde(default)]
+    pub code_action_kinds: Option<Vec<lsp::CodeActionKind>>,
+}
+
+impl LanguageServerManifestEntry {
+    /// Returns the list of languages for the language server.
+    ///
+    /// Prefer this over accessing the `language` or `languages` fields directly,
+    /// as we currently support both.
+    ///
+    /// We can replace this with just field access for the `languages` field once
+    /// we have removed `language`.
+    pub fn languages(&self) -> impl IntoIterator<Item = LanguageName> + '_ {
+        let language = if self.languages.is_empty() {
+            self.language.clone()
+        } else {
+            None
+        };
+        self.languages.iter().cloned().chain(language)
+    }
+}
+
+#[derive(Clone, PartialEq, Eq, Debug, Deserialize, Serialize)]
+pub struct SlashCommandManifestEntry {
+    pub description: String,
+    pub requires_argument: bool,
+}
+
+#[derive(Clone, PartialEq, Eq, Debug, Deserialize, Serialize)]
+pub struct IndexedDocsProviderEntry {}
+
+impl ExtensionManifest {
+    pub async fn load(fs: Arc<dyn Fs>, extension_dir: &Path) -> Result<Self> {
+        let extension_name = extension_dir
+            .file_name()
+            .and_then(OsStr::to_str)
+            .ok_or_else(|| anyhow!("invalid extension name"))?;
+
+        let mut extension_manifest_path = extension_dir.join("extension.json");
+        if fs.is_file(&extension_manifest_path).await {
+            let manifest_content = fs
+                .load(&extension_manifest_path)
+                .await
+                .with_context(|| format!("failed to load {extension_name} extension.json"))?;
+            let manifest_json = serde_json::from_str::<OldExtensionManifest>(&manifest_content)
+                .with_context(|| {
+                    format!("invalid extension.json for extension {extension_name}")
+                })?;
+
+            Ok(manifest_from_old_manifest(manifest_json, extension_name))
+        } else {
+            extension_manifest_path.set_extension("toml");
+            let manifest_content = fs
+                .load(&extension_manifest_path)
+                .await
+                .with_context(|| format!("failed to load {extension_name} extension.toml"))?;
+            toml::from_str(&manifest_content)
+                .with_context(|| format!("invalid extension.json for extension {extension_name}"))
+        }
+    }
+}
+
+fn manifest_from_old_manifest(
+    manifest_json: OldExtensionManifest,
+    extension_id: &str,
+) -> ExtensionManifest {
+    ExtensionManifest {
+        id: extension_id.into(),
+        name: manifest_json.name,
+        version: manifest_json.version,
+        description: manifest_json.description,
+        repository: manifest_json.repository,
+        authors: manifest_json.authors,
+        schema_version: SchemaVersion::ZERO,
+        lib: Default::default(),
+        themes: {
+            let mut themes = manifest_json.themes.into_values().collect::<Vec<_>>();
+            themes.sort();
+            themes.dedup();
+            themes
+        },
+        languages: {
+            let mut languages = manifest_json.languages.into_values().collect::<Vec<_>>();
+            languages.sort();
+            languages.dedup();
+            languages
+        },
+        grammars: manifest_json
+            .grammars
+            .into_keys()
+            .map(|grammar_name| (grammar_name, Default::default()))
+            .collect(),
+        language_servers: Default::default(),
+        slash_commands: BTreeMap::default(),
+        indexed_docs_providers: BTreeMap::default(),
+        snippets: None,
+    }
+}