Windows: Fix issues with paths in extensions (#37811)

### Background

Zed extensions use WASI to access the file-system. They only have
read-write access to one specific folder called their work dir. But
extensions do need to be able to *refer* to other arbitrary files on the
user's machine. For instance, extensions need to be able to look up
existing binaries on the user's `PATH`, and request that Zed invoke them
as language servers. Similarly, extensions can create paths to files in
the user's project, and use them as arguments in commands that Zed
should run. For these reasons, we pass *real* paths back and forth
between the host and extensions; we don't try to abstract over the
file-system with some virtualization scheme.

On Windows, this results in a bit of mismatch, because `wasi-libc` uses
*unix-like* path conventions (and thus, so does the Rust standard
library when compiling to WASI).

### Change 1 - Fixing `current_dir`

In order to keep the extension API minimal, extensions use the standard
library function`env::current_dir()` to query the location of their
"work" directory. Previously, when initializing extensions, we used the
`env::set_current_dir` function to set their work directory, but on
Windows, where absolute paths typically begin with a drive letter, like
`C:`, the [`wasi-libc` implementation of
`chdir`](d1793637d8/libc-bottom-half/sources/chdir.c (L21))
was prepending an extra forward slash to the path, which caused
`current_dir()` to return an invalid path.

See https://github.com/bytecodealliance/wasmtime/issues/10415

In this PR, I've switched our extension initialization function to
*bypass* wasi-libc's `chdir` function, and instead write directly to
wasi-libc's private, internal state. This is a bit of a hack, but it
causes the `current_dir()` function to do what we want on Windows
without any changes to extensions' source code.

### Change 2 - Working around WASI's relative path handling

Once `current_dir` was fixed (giving us correct absolute paths on
Windows), @kubkon and I discovered that without the spurious leading `/`
character, windows absolute paths were no longer accepted by Rust's
`std::fs` APIs, because they were now recognized as relative paths, and
were being appended to the working directory.

We first tried to override the `__wasilibc_find_abspath` function in
`wasi-libc` to make it recognize windows absolute paths as being
absolute, but that functionality is difficult to override. Eventually
@kubkon realized that we could prevent WASI-libc's CWD handling from
being linked into the WASM file by overriding the `chdir` function.
wasi-libc is designed so that if you don't use their `chdir` function,
then all paths will be interpreted as relative to `/`. This makes
absolute paths behave correctly. Then, in order to make *relative* paths
work again, we simply add a preopen for `.`. Relative paths will match
that.

### Next Steps

This is a change to `zed-extension-api`, so we do need to update every
Zed extension to use the new version, in order for them to work on
windows.

Release Notes:

- N/A

---------

Co-authored-by: Jakub Konka <kubkon@jakubkonka.com>

Cargo.lock

@@ -9108,6 +9108,7 @@ dependencies = [
  "futures 0.3.31",
  "gpui",
  "language",
+ "log",
  "lsp",
  "project",
  "serde",
@@ -20675,7 +20676,7 @@ dependencies = [
 
 [[package]]
 name = "zed_extension_api"
-version = "0.6.0"
+version = "0.7.0"
 dependencies = [
  "serde",
  "serde_json",
@@ -20722,7 +20723,7 @@ dependencies = [
 name = "zed_test_extension"
 version = "0.1.0"
 dependencies = [
- "zed_extension_api 0.6.0",
+ "zed_extension_api 0.7.0",
 ]
 
 [[package]]

crates/extension_api/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "zed_extension_api"
-version = "0.6.0"
+version = "0.7.0"
 description = "APIs for creating Zed extensions in Rust"
 repository = "https://github.com/zed-industries/zed"
 documentation = "https://docs.rs/zed_extension_api"

crates/extension_api/src/extension_api.rs

@@ -267,9 +267,43 @@ pub trait Extension: Send + Sync {
 #[macro_export]
 macro_rules! register_extension {
     ($extension_type:ty) => {
+        #[cfg(target_os = "wasi")]
+        mod wasi_ext {
+            unsafe extern "C" {
+                static mut errno: i32;
+                pub static mut __wasilibc_cwd: *mut std::ffi::c_char;
+            }
+
+            pub fn init_cwd() {
+                unsafe {
+                    // Ensure that our chdir function is linked, instead of the
+                    // one from wasi-libc in the chdir.o translation unit. Otherwise
+                    // we risk linking in `__wasilibc_find_relpath_alloc` which
+                    // is a weak symbol and is being used by
+                    // `__wasilibc_find_relpath`, which we do not want on
+                    // Windows.
+                    chdir(std::ptr::null());
+
+                    __wasilibc_cwd = std::ffi::CString::new(std::env::var("PWD").unwrap())
+                        .unwrap()
+                        .into_raw()
+                        .cast();
+                }
+            }
+
+            #[unsafe(no_mangle)]
+            pub unsafe extern "C" fn chdir(raw_path: *const std::ffi::c_char) -> i32 {
+                // Forbid extensions from changing CWD and so return an appropriate error code.
+                errno = 58; // NOTSUP
+                return -1;
+            }
+        }
+
         #[unsafe(export_name = "init-extension")]
         pub extern "C" fn __init_extension() {
-            std::env::set_current_dir(std::env::var("PWD").unwrap()).unwrap();
+            #[cfg(target_os = "wasi")]
+            wasi_ext::init_cwd();
+
             zed_extension_api::register_extension(|| {
                 Box::new(<$extension_type as zed_extension_api::Extension>::new())
             });

crates/extension_host/src/extension_host.rs

@@ -587,6 +587,10 @@ impl ExtensionStore {
     /// This can be used to make certain functionality provided by extensions
     /// available out-of-the-box.
     pub fn auto_install_extensions(&mut self, cx: &mut Context<Self>) {
+        if cfg!(test) {
+            return;
+        }
+
         let extension_settings = ExtensionSettings::get_global(cx);
 
         let extensions_to_install = extension_settings

crates/extension_host/src/extension_store_test.rs

@@ -531,7 +531,6 @@ async fn test_extension_store(cx: &mut TestAppContext) {
 // `let fake_server = fake_servers.next().await.unwrap();`.
 // Reenable this test when we figure out why.
 #[gpui::test]
-#[cfg_attr(target_os = "windows", ignore)]
 async fn test_extension_store_with_test_extension(cx: &mut TestAppContext) {
     init_test(cx);
     cx.executor().allow_parking();
@@ -546,7 +545,7 @@ async fn test_extension_store_with_test_extension(cx: &mut TestAppContext) {
     let test_extension_dir = root_dir.join("extensions").join(test_extension_id);
 
     let fs = Arc::new(RealFs::new(None, cx.executor()));
-    let extensions_dir = TempTree::new(json!({
+    let extensions_tree = TempTree::new(json!({
         "installed": {},
         "work": {}
     }));
@@ -554,7 +553,7 @@ async fn test_extension_store_with_test_extension(cx: &mut TestAppContext) {
         "test.gleam": ""
     }));
 
-    let extensions_dir = extensions_dir.path().canonicalize().unwrap();
+    let extensions_dir = extensions_tree.path().canonicalize().unwrap();
     let project_dir = project_dir.path().canonicalize().unwrap();
 
     let project = Project::test(fs.clone(), [project_dir.as_path()], cx).await;
@@ -618,6 +617,10 @@ async fn test_extension_store_with_test_extension(cx: &mut TestAppContext) {
                                     {
                                         "name": format!("gleam-{version}-aarch64-unknown-linux-musl.tar.gz"),
                                         "browser_download_url": asset_download_uri
+                                    },
+                                    {
+                                        "name": format!("gleam-{version}-x86_64-pc-windows-msvc.tar.gz"),
+                                        "browser_download_url": asset_download_uri
                                     }
                                 ]
                             }
@@ -714,13 +717,17 @@ async fn test_extension_store_with_test_extension(cx: &mut TestAppContext) {
         .await
         .unwrap();
 
-    // todo(windows)
-    // This test hangs here on Windows.
     let fake_server = fake_servers.next().await.unwrap();
-    let expected_server_path =
-        extensions_dir.join(format!("work/{test_extension_id}/gleam-v1.2.3/gleam"));
+    let work_dir = extensions_dir.join(format!("work/{test_extension_id}"));
+    let expected_server_path = work_dir.join("gleam-v1.2.3/gleam");
     let expected_binary_contents = language_server_version.lock().binary_contents.clone();
 
+    // check that IO operations in extension work correctly
+    assert!(work_dir.join("dir-created-with-rel-path").exists());
+    assert!(work_dir.join("dir-created-with-abs-path").exists());
+    assert!(work_dir.join("file-created-with-abs-path").exists());
+    assert!(work_dir.join("file-created-with-rel-path").exists());
+
     assert_eq!(fake_server.binary.path, expected_server_path);
     assert_eq!(fake_server.binary.arguments, [OsString::from("lsp")]);
     assert_eq!(
@@ -826,7 +833,9 @@ async fn test_extension_store_with_test_extension(cx: &mut TestAppContext) {
     // Reload the extension, clearing its cache.
     // Start a new instance of the language server.
     extension_store
-        .update(cx, |store, cx| store.reload(Some("gleam".into()), cx))
+        .update(cx, |store, cx| {
+            store.reload(Some("test-extension".into()), cx)
+        })
         .await;
     cx.executor().run_until_parked();
     project.update(cx, |project, cx| {

crates/extension_host/src/wasm_host.rs

@@ -37,6 +37,7 @@ use std::{
     sync::Arc,
 };
 use task::{DebugScenario, SpawnInTerminal, TaskTemplate, ZedDebugConfig};
+use util::paths::SanitizedPath;
 use wasmtime::{
     CacheStore, Engine, Store,
     component::{Component, ResourceTable},
@@ -607,7 +608,6 @@ impl WasmHost {
 
             let component = Component::from_binary(&this.engine, &wasm_bytes)
                 .context("failed to compile wasm component")?;
-
             let mut store = wasmtime::Store::new(
                 &this.engine,
                 WasmState {
@@ -666,19 +666,17 @@ impl WasmHost {
 
         let file_perms = wasi::FilePerms::all();
         let dir_perms = wasi::DirPerms::all();
+        let path = SanitizedPath::new(&extension_work_dir);
 
-        Ok(wasi::WasiCtxBuilder::new()
-            .inherit_stdio()
-            .preopened_dir(&extension_work_dir, ".", dir_perms, file_perms)?
-            .preopened_dir(
-                &extension_work_dir,
-                extension_work_dir.to_string_lossy(),
-                dir_perms,
-                file_perms,
-            )?
-            .env("PWD", extension_work_dir.to_string_lossy())
-            .env("RUST_BACKTRACE", "full")
-            .build())
+        let mut ctx = wasi::WasiCtxBuilder::new();
+        ctx.inherit_stdio()
+            .env("PWD", path.to_string())
+            .env("RUST_BACKTRACE", "full");
+
+        ctx.preopened_dir(&path, ".", dir_perms, file_perms)?;
+        ctx.preopened_dir(&path, path.to_string(), dir_perms, file_perms)?;
+
+        Ok(ctx.build())
     }
 
     pub fn writeable_path_from_extension(&self, id: &Arc<str>, path: &Path) -> Result<PathBuf> {

crates/fs/src/fs.rs

@@ -343,7 +343,19 @@ impl Fs for RealFs {
 
         #[cfg(windows)]
         if smol::fs::metadata(&target).await?.is_dir() {
-            smol::fs::windows::symlink_dir(target, path).await?
+            let status = smol::process::Command::new("cmd")
+                .args(["/C", "mklink", "/J"])
+                .args([path, target.as_path()])
+                .status()
+                .await?;
+
+            if !status.success() {
+                return Err(anyhow::anyhow!(
+                    "Failed to create junction from {:?} to {:?}",
+                    path,
+                    target
+                ));
+            }
         } else {
             smol::fs::windows::symlink_file(target, path).await?
         }

crates/language_extension/Cargo.toml

@@ -20,6 +20,7 @@ futures.workspace = true
 fs.workspace = true
 gpui.workspace = true
 language.workspace = true
+log.workspace = true
 lsp.workspace = true
 project.workspace = true
 serde.workspace = true

crates/language_extension/src/extension_lsp_adapter.rs

@@ -124,6 +124,11 @@ impl ExtensionLanguageServerProxy for LanguageServerRegistryProxy {
         language_server_id: LanguageServerName,
         status: BinaryStatus,
     ) {
+        log::debug!(
+            "updating binary status for {} to {:?}",
+            language_server_id,
+            status
+        );
         self.language_registry
             .update_lsp_binary_status(language_server_id, status);
     }

extensions/test-extension/extension.toml

@@ -17,4 +17,9 @@ commit = "8432ffe32ccd360534837256747beb5b1c82fca1"
 [[capabilities]]
 kind = "process:exec"
 command = "echo"
-args = ["hello!"]
+args = ["hello from a child process!"]
+
+[[capabilities]]
+kind = "process:exec"
+command = "cmd"
+args = ["/C", "echo", "hello from a child process!"]

extensions/test-extension/src/test_extension.rs

@@ -14,9 +14,37 @@ impl TestExtension {
         language_server_id: &LanguageServerId,
         _worktree: &zed::Worktree,
     ) -> Result<String> {
-        let echo_output = Command::new("echo").arg("hello!").output()?;
+        let (platform, arch) = zed::current_platform();
 
-        println!("{}", String::from_utf8_lossy(&echo_output.stdout));
+        let current_dir = std::env::current_dir().unwrap();
+        println!("current_dir: {}", current_dir.display());
+
+        fs::create_dir_all(current_dir.join("dir-created-with-abs-path")).unwrap();
+        fs::create_dir_all("./dir-created-with-rel-path").unwrap();
+        fs::write("file-created-with-rel-path", b"contents 1").unwrap();
+        fs::write(
+            current_dir.join("file-created-with-abs-path"),
+            b"contents 2",
+        )
+        .unwrap();
+        assert_eq!(
+            fs::read("file-created-with-rel-path").unwrap(),
+            b"contents 1"
+        );
+        assert_eq!(
+            fs::read("file-created-with-abs-path").unwrap(),
+            b"contents 2"
+        );
+
+        let command = match platform {
+            zed::Os::Linux | zed::Os::Mac => Command::new("echo"),
+            zed::Os::Windows => Command::new("cmd").args(["/C", "echo"]),
+        };
+        let output = command.arg("hello from a child process!").output()?;
+        println!(
+            "command output: {}",
+            String::from_utf8_lossy(&output.stdout).trim()
+        );
 
         if let Some(path) = &self.cached_binary_path
             && fs::metadata(path).is_ok_and(|stat| stat.is_file())
@@ -36,9 +64,18 @@ impl TestExtension {
             },
         )?;
 
-        let (platform, arch) = zed::current_platform();
+        let ext = "tar.gz";
+        let download_type = zed::DownloadedFileType::GzipTar;
+
+        // Do this if you want to actually run this extension -
+        // the actual asset is a .zip. But the integration test is simpler
+        // if every platform uses .tar.gz.
+        //
+        // ext = "zip";
+        // download_type = zed::DownloadedFileType::Zip;
+
         let asset_name = format!(
-            "gleam-{version}-{arch}-{os}.tar.gz",
+            "gleam-{version}-{arch}-{os}.{ext}",
             version = release.version,
             arch = match arch {
                 zed::Architecture::Aarch64 => "aarch64",
@@ -67,18 +104,21 @@ impl TestExtension {
                 &zed::LanguageServerInstallationStatus::Downloading,
             );
 
-            zed::download_file(
-                &asset.download_url,
-                &version_dir,
-                zed::DownloadedFileType::GzipTar,
-            )
-            .map_err(|e| format!("failed to download file: {e}"))?;
+            zed::download_file(&asset.download_url, &version_dir, download_type)
+                .map_err(|e| format!("failed to download file: {e}"))?;
+
+            zed::set_language_server_installation_status(
+                language_server_id,
+                &zed::LanguageServerInstallationStatus::None,
+            );
 
             let entries =
                 fs::read_dir(".").map_err(|e| format!("failed to list working directory {e}"))?;
             for entry in entries {
                 let entry = entry.map_err(|e| format!("failed to load directory entry {e}"))?;
-                if entry.file_name().to_str() != Some(&version_dir) {
+                let filename = entry.file_name();
+                let filename = filename.to_str().unwrap();
+                if filename.starts_with("gleam-") && filename != version_dir {
                     fs::remove_dir_all(entry.path()).ok();
                 }
             }