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.

Author: Mark-Simulacrum

Cargo.lock

@@ -3363,6 +3363,7 @@ dependencies = [
  "smallvec 1.4.0",
  "stable_deref_trait",
  "stacker",
+ "tempfile",
  "tracing",
  "winapi 0.3.8",
 ]

src/librustc_codegen_ssa/back/link.rs

@@ -1,4 +1,5 @@
 use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::temp_dir::MaybeTempDir;
 use rustc_fs_util::fix_windows_verbatim_for_gcc;
 use rustc_hir::def_id::CrateNum;
 use rustc_middle::middle::cstore::{EncodedMetadata, LibSource, NativeLib};
@@ -23,7 +24,7 @@ use super::rpath::{self, RPathConfig};
 use crate::{looks_like_rust_object_file, CodegenResults, CrateInfo, METADATA_FILENAME};
 
 use cc::windows_registry;
-use tempfile::{Builder as TempFileBuilder, TempDir};
+use tempfile::Builder as TempFileBuilder;
 
 use std::ffi::OsString;
 use std::path::{Path, PathBuf};
@@ -70,35 +71,29 @@ pub fn link_binary<'a, B: ArchiveBuilder<'a>>(
             }
         });
 
-        let tmpdir = TempFileBuilder::new()
-            .prefix("rustc")
-            .tempdir()
-            .unwrap_or_else(|err| sess.fatal(&format!("couldn't create a temp dir: {}", err)));
-
         if outputs.outputs.should_codegen() {
+            let tmpdir = TempFileBuilder::new()
+                .prefix("rustc")
+                .tempdir()
+                .unwrap_or_else(|err| sess.fatal(&format!("couldn't create a temp dir: {}", err)));
+            let path = MaybeTempDir::new(tmpdir, sess.opts.cg.save_temps);
             let out_filename = out_filename(sess, crate_type, outputs, crate_name);
             match crate_type {
                 CrateType::Rlib => {
                     let _timer = sess.timer("link_rlib");
-                    link_rlib::<B>(
-                        sess,
-                        codegen_results,
-                        RlibFlavor::Normal,
-                        &out_filename,
-                        &tmpdir,
-                    )
-                    .build();
+                    link_rlib::<B>(sess, codegen_results, RlibFlavor::Normal, &out_filename, &path)
+                        .build();
                 }
                 CrateType::Staticlib => {
-                    link_staticlib::<B>(sess, codegen_results, &out_filename, &tmpdir);
+                    link_staticlib::<B>(sess, codegen_results, &out_filename, &path);
                 }
                 _ => {
                     link_natively::<B>(
                         sess,
                         crate_type,
                         &out_filename,
                         codegen_results,
-                        tmpdir.path(),
+                        path.as_ref(),
                         target_cpu,
                     );
                 }
@@ -107,10 +102,6 @@ pub fn link_binary<'a, B: ArchiveBuilder<'a>>(
                 sess.parse_sess.span_diagnostic.emit_artifact_notification(&out_filename, "link");
             }
         }
-
-        if sess.opts.cg.save_temps {
-            let _ = tmpdir.into_path();
-        }
     }
 
     // Remove the temporary object file and metadata if we aren't saving temps
@@ -279,8 +270,8 @@ pub fn each_linked_rlib(
 /// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
 /// directory being searched for `extern crate` (observing an incomplete file).
 /// The returned path is the temporary file containing the complete metadata.
-pub fn emit_metadata(sess: &Session, metadata: &EncodedMetadata, tmpdir: &TempDir) -> PathBuf {
-    let out_filename = tmpdir.path().join(METADATA_FILENAME);
+pub fn emit_metadata(sess: &Session, metadata: &EncodedMetadata, tmpdir: &MaybeTempDir) -> PathBuf {
+    let out_filename = tmpdir.as_ref().join(METADATA_FILENAME);
     let result = fs::write(&out_filename, &metadata.raw_data);
 
     if let Err(e) = result {
@@ -301,7 +292,7 @@ fn link_rlib<'a, B: ArchiveBuilder<'a>>(
     codegen_results: &CodegenResults,
     flavor: RlibFlavor,
     out_filename: &Path,
-    tmpdir: &TempDir,
+    tmpdir: &MaybeTempDir,
 ) -> B {
     info!("preparing rlib to {:?}", out_filename);
     let mut ab = <B as ArchiveBuilder>::new(sess, out_filename, None);
@@ -406,7 +397,7 @@ fn link_staticlib<'a, B: ArchiveBuilder<'a>>(
     sess: &'a Session,
     codegen_results: &CodegenResults,
     out_filename: &Path,
-    tempdir: &TempDir,
+    tempdir: &MaybeTempDir,
 ) {
     let mut ab =
         link_rlib::<B>(sess, codegen_results, RlibFlavor::StaticlibBase, out_filename, tempdir);

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"

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);
 

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 }
+    }
+}

src/librustc_interface/passes.rs

@@ -9,6 +9,7 @@ use rustc_ast::{self, ast, visit};
 use rustc_codegen_ssa::back::link::emit_metadata;
 use rustc_codegen_ssa::traits::CodegenBackend;
 use rustc_data_structures::sync::{par_iter, Lrc, OnceCell, ParallelIterator, WorkerLocal};
+use rustc_data_structures::temp_dir::MaybeTempDir;
 use rustc_data_structures::{box_region_allow_access, declare_box_region_type, parallel};
 use rustc_errors::{ErrorReported, PResult};
 use rustc_expand::base::ExtCtxt;
@@ -974,6 +975,7 @@ fn encode_and_write_metadata(
             .prefix("rmeta")
             .tempdir_in(out_filename.parent().unwrap())
             .unwrap_or_else(|err| tcx.sess.fatal(&format!("couldn't create a temp dir: {}", err)));
+        let metadata_tmpdir = MaybeTempDir::new(metadata_tmpdir, tcx.sess.opts.cg.save_temps);
         let metadata_filename = emit_metadata(tcx.sess, &metadata, &metadata_tmpdir);
         if let Err(e) = fs::rename(&metadata_filename, &out_filename) {
             tcx.sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));