Rollup merge of #75315 - Mark-Simulacrum:save-temps, r=ecstatic-morse

Avoid deleting temporary files on error

Previously if the compiler error'd, fatally, then temporary directories which
should be preserved by -Csave-temps would be deleted due to fatal compiler
errors being implemented as panics.

cc @infinity0

(Hopefully) fixes #75275, but I haven't tested

3 files changed, 36 insertions, 0 deletions

diff --git a/src/librustc_data_structures/Cargo.toml b/src/librustc_data_structures/Cargo.toml
index d0dbad5d2af..36c32e60031 100644
--- a/src/librustc_data_structures/Cargo.toml
+++ b/src/librustc_data_structures/Cargo.toml
@@ -30,6 +30,7 @@ bitflags = "1.2.1"
 measureme = "0.7.1"
 libc = "0.2"
 stacker = "0.1.9"
+tempfile = "3.0.5"
 
 [dependencies.parking_lot]
 version = "0.10"
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index 0b2e7cda1b4..3884fc05105 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -95,6 +95,7 @@ pub mod vec_linked_list;
 pub mod work_queue;
 pub use atomic_ref::AtomicRef;
 pub mod frozen;
+pub mod temp_dir;
 
 pub struct OnDrop<F: Fn()>(pub F);
 
diff --git a/src/librustc_data_structures/temp_dir.rs b/src/librustc_data_structures/temp_dir.rs
new file mode 100644
index 00000000000..0d9b3e3ca25
--- /dev/null
+++ b/src/librustc_data_structures/temp_dir.rs
@@ -0,0 +1,34 @@
+use std::mem::ManuallyDrop;
+use std::path::Path;
+use tempfile::TempDir;
+
+/// This is used to avoid TempDir being dropped on error paths unintentionally.
+#[derive(Debug)]
+pub struct MaybeTempDir {
+    dir: ManuallyDrop<TempDir>,
+    // Whether the TempDir should be deleted on drop.
+    keep: bool,
+}
+
+impl Drop for MaybeTempDir {
+    fn drop(&mut self) {
+        // Safety: We are in the destructor, and no further access will
+        // occur.
+        let dir = unsafe { ManuallyDrop::take(&mut self.dir) };
+        if self.keep {
+            dir.into_path();
+        }
+    }
+}
+
+impl AsRef<Path> for MaybeTempDir {
+    fn as_ref(&self) -> &Path {
+        self.dir.path()
+    }
+}
+
+impl MaybeTempDir {
+    pub fn new(dir: TempDir, keep_on_drop: bool) -> MaybeTempDir {
+        MaybeTempDir { dir: ManuallyDrop::new(dir), keep: keep_on_drop }
+    }
+}