chore(tests): add `.use_symlinked_temp_dir()` to `TestBuilder` (#19435)

This allows easily using a symlinked temporary directory, which is
useful for debugging issues locally that happen on the CI with a
symlinked temporary directory. For example:

```rs
let context = TestContextBuilder::new()
    .use_temp_cwd()
    .use_symlinked_temp_dir() // add this
    .build();
```

3 files changed, 85 insertions, 11 deletions

diff --git a/test_util/src/builders.rs b/test_util/src/builders.rs
index a000e5bcd..049ccbd67 100644
--- a/test_util/src/builders.rs
+++ b/test_util/src/builders.rs
@@ -31,6 +31,7 @@ pub struct TestContextBuilder {
   use_http_server: bool,
   use_temp_cwd: bool,
   use_separate_deno_dir: bool,
+  use_symlinked_temp_dir: bool,
   /// Copies the files at the specified directory in the "testdata" directory
   /// to the temp folder and runs the test from there. This is useful when
   /// the test creates files in the testdata directory (ex. a node_modules folder)
@@ -59,6 +60,18 @@ impl TestContextBuilder {
     self
   }
 
+  /// Causes the temp directory to be symlinked to a target directory
+  /// which is useful for debugging issues that only show up on the CI.
+  ///
+  /// Note: This method is not actually deprecated, it's just the CI
+  /// does this by default so there's no need to check in any code that
+  /// uses this into the repo. This is just for debugging purposes.
+  #[deprecated]
+  pub fn use_symlinked_temp_dir(mut self) -> Self {
+    self.use_symlinked_temp_dir = true;
+    self
+  }
+
   /// By default, the temp_dir and the deno_dir will be shared.
   /// In some cases, that might cause an issue though, so calling
   /// this will use a separate directory for the deno dir and the
@@ -110,6 +123,11 @@ impl TestContextBuilder {
     } else {
       deno_dir.clone()
     };
+    let temp_dir = if self.use_symlinked_temp_dir {
+      TempDir::new_symlinked(temp_dir)
+    } else {
+      temp_dir
+    };
     let testdata_dir = if let Some(temp_copy_dir) = &self.copy_temp_dir {
       let test_data_path = testdata_path().join(temp_copy_dir);
       let temp_copy_dir = temp_dir.path().join(temp_copy_dir);
diff --git a/test_util/src/lsp.rs b/test_util/src/lsp.rs
index 831df28e9..87dfaf6f9 100644
--- a/test_util/src/lsp.rs
+++ b/test_util/src/lsp.rs
@@ -616,7 +616,7 @@ impl LspClient {
     config: Value,
   ) {
     let mut builder = InitializeParamsBuilder::new();
-    builder.set_root_uri(self.context.deno_dir().uri());
+    builder.set_root_uri(self.context.temp_dir().uri());
     do_build(&mut builder);
     self.write_request("initialize", builder.build());
     self.write_notification("initialized", json!({}));
diff --git a/test_util/src/temp_dir.rs b/test_util/src/temp_dir.rs
index f66bf1398..4ec6eb9f8 100644
--- a/test_util/src/temp_dir.rs
+++ b/test_util/src/temp_dir.rs
@@ -2,11 +2,46 @@
 
 use std::fs;
 use std::path::Path;
+use std::path::PathBuf;
 use std::sync::Arc;
 
 use anyhow::Context;
 use lsp_types::Url;
 
+enum TempDirInner {
+  TempDir(tempfile::TempDir),
+  Path(PathBuf),
+  Symlinked {
+    symlink: Arc<TempDirInner>,
+    target: Arc<TempDirInner>,
+  },
+}
+
+impl TempDirInner {
+  pub fn path(&self) -> &Path {
+    match self {
+      Self::Path(path) => path.as_path(),
+      Self::TempDir(dir) => dir.path(),
+      Self::Symlinked { symlink, .. } => symlink.path(),
+    }
+  }
+
+  pub fn target_path(&self) -> &Path {
+    match self {
+      TempDirInner::Symlinked { target, .. } => target.target_path(),
+      _ => self.path(),
+    }
+  }
+}
+
+impl Drop for TempDirInner {
+  fn drop(&mut self) {
+    if let Self::Path(path) = self {
+      _ = fs::remove_dir_all(path);
+    }
+  }
+}
+
 /// For creating temporary directories in tests.
 ///
 /// This was done because `tempfiles::TempDir` was very slow on Windows.
@@ -14,7 +49,7 @@ use lsp_types::Url;
 /// Note: Do not use this in actual code as this does not protect against
 /// "insecure temporary file" security vulnerabilities.
 #[derive(Clone)]
-pub struct TempDir(Arc<tempfile::TempDir>);
+pub struct TempDir(Arc<TempDirInner>);
 
 impl Default for TempDir {
   fn default() -> Self {
@@ -35,6 +70,23 @@ impl TempDir {
     Self::new_inner(&std::env::temp_dir(), Some(prefix))
   }
 
+  pub fn new_with_path(path: &Path) -> Self {
+    Self(Arc::new(TempDirInner::Path(path.to_path_buf())))
+  }
+
+  pub fn new_symlinked(target: TempDir) -> Self {
+    let target_path = target.path();
+    let path = target_path.parent().unwrap().join(format!(
+      "{}_symlinked",
+      target_path.file_name().unwrap().to_str().unwrap()
+    ));
+    target.symlink_dir(target.path(), &path);
+    TempDir(Arc::new(TempDirInner::Symlinked {
+      target: target.0,
+      symlink: Self::new_with_path(&path).0,
+    }))
+  }
+
   /// Create a new temporary directory with the given prefix as part of its name, if specified.
   fn new_inner(parent_dir: &Path, prefix: Option<&str>) -> Self {
     let mut builder = tempfile::Builder::new();
@@ -42,7 +94,7 @@ impl TempDir {
     let dir = builder
       .tempdir_in(parent_dir)
       .expect("Failed to create a temporary directory");
-    Self(dir.into())
+    Self(Arc::new(TempDirInner::TempDir(dir)))
   }
 
   pub fn uri(&self) -> Url {
@@ -50,35 +102,39 @@ impl TempDir {
   }
 
   pub fn path(&self) -> &Path {
-    let inner = &self.0;
-    inner.path()
+    self.0.path()
+  }
+
+  /// The resolved final target path if this is a symlink.
+  pub fn target_path(&self) -> &Path {
+    self.0.target_path()
   }
 
   pub fn create_dir_all(&self, path: impl AsRef<Path>) {
-    fs::create_dir_all(self.path().join(path)).unwrap();
+    fs::create_dir_all(self.target_path().join(path)).unwrap();
   }
 
   pub fn remove_file(&self, path: impl AsRef<Path>) {
-    fs::remove_file(self.path().join(path)).unwrap();
+    fs::remove_file(self.target_path().join(path)).unwrap();
   }
 
   pub fn remove_dir_all(&self, path: impl AsRef<Path>) {
-    fs::remove_dir_all(self.path().join(path)).unwrap();
+    fs::remove_dir_all(self.target_path().join(path)).unwrap();
   }
 
   pub fn read_to_string(&self, path: impl AsRef<Path>) -> String {
-    let file_path = self.path().join(path);
+    let file_path = self.target_path().join(path);
     fs::read_to_string(&file_path)
       .with_context(|| format!("Could not find file: {}", file_path.display()))
       .unwrap()
   }
 
   pub fn rename(&self, from: impl AsRef<Path>, to: impl AsRef<Path>) {
-    fs::rename(self.path().join(from), self.path().join(to)).unwrap();
+    fs::rename(self.target_path().join(from), self.path().join(to)).unwrap();
   }
 
   pub fn write(&self, path: impl AsRef<Path>, text: impl AsRef<str>) {
-    fs::write(self.path().join(path), text.as_ref()).unwrap();
+    fs::write(self.target_path().join(path), text.as_ref()).unwrap();
   }
 
   pub fn symlink_dir(