Prepend temp files with a string per invocation of rustc

Author: compiler-errors

Cargo.lock

@@ -3896,6 +3896,7 @@ dependencies = [
 name = "rustc_interface"
 version = "0.0.0"
 dependencies = [
+ "rand 0.9.0",
  "rustc-rayon",
  "rustc-rayon-core",
  "rustc_abi",

compiler/rustc_driver_impl/src/lib.rs

@@ -670,7 +670,7 @@ fn print_crate_info(
                     // no crate attributes, print out an error and exit
                     return Compilation::Continue;
                 };
-                let t_outputs = rustc_interface::util::build_output_filenames(attrs, sess);
+                let t_outputs = rustc_interface::util::build_output_filenames(attrs, sess, None);
                 let crate_name = passes::get_crate_name(sess, attrs);
                 let crate_types = collect_crate_types(sess, attrs);
                 for &style in &crate_types {

compiler/rustc_interface/Cargo.toml

@@ -5,6 +5,7 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
+rand = "0.9.0"
 rustc-rayon = { version = "0.5.0" }
 rustc-rayon-core = { version = "0.5.0" }
 rustc_ast = { path = "../rustc_ast" }

compiler/rustc_interface/src/passes.rs

@@ -5,8 +5,10 @@ use std::path::{Path, PathBuf};
 use std::sync::{Arc, LazyLock, OnceLock};
 use std::{env, fs, iter};
 
+use rand::{RngCore, rng};
 use rustc_ast as ast;
 use rustc_codegen_ssa::traits::CodegenBackend;
+use rustc_data_structures::base_n::{CASE_INSENSITIVE, ToBaseN};
 use rustc_data_structures::parallel;
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::sync::{AppendOnlyIndexVec, FreezeLock, WorkerLocal};
@@ -800,7 +802,13 @@ pub fn create_and_enter_global_ctxt<T, F: for<'tcx> FnOnce(TyCtxt<'tcx>) -> T>(
         sess.opts.cg.metadata.clone(),
         sess.cfg_version,
     );
-    let outputs = util::build_output_filenames(&pre_configured_attrs, sess);
+
+    let invocation_temp = sess
+        .opts
+        .incremental
+        .as_ref()
+        .map(|_| rng().next_u32().to_base_fixed_len(CASE_INSENSITIVE).to_string());
+    let outputs = util::build_output_filenames(&pre_configured_attrs, sess, invocation_temp);
 
     let dep_type = DepsType { dep_names: rustc_query_impl::dep_kind_names() };
     let dep_graph = setup_dep_graph(sess, crate_name, &dep_type);

compiler/rustc_interface/src/util.rs

@@ -486,7 +486,11 @@ fn multiple_output_types_to_stdout(
     }
 }
 
-pub fn build_output_filenames(attrs: &[ast::Attribute], sess: &Session) -> OutputFilenames {
+pub fn build_output_filenames(
+    attrs: &[ast::Attribute],
+    sess: &Session,
+    invocation_temp: Option<String>,
+) -> OutputFilenames {
     if multiple_output_types_to_stdout(
         &sess.opts.output_types,
         sess.io.output_file == Some(OutFileName::Stdout),
@@ -515,6 +519,7 @@ pub fn build_output_filenames(attrs: &[ast::Attribute], sess: &Session) -> Outpu
                 crate_name.unwrap_or_else(|| stem.replace('-', "_")),
                 stem,
                 None,
+                invocation_temp,
                 sess.io.temps_dir.clone(),
                 sess.opts.cg.extra_filename.clone(),
                 sess.opts.output_types.clone(),
@@ -544,6 +549,7 @@ pub fn build_output_filenames(attrs: &[ast::Attribute], sess: &Session) -> Outpu
                 crate_name.unwrap_or_else(|| out_filestem.replace('-', "_")),
                 out_filestem,
                 ofile,
+                invocation_temp,
                 sess.io.temps_dir.clone(),
                 sess.opts.cg.extra_filename.clone(),
                 sess.opts.output_types.clone(),

compiler/rustc_session/src/config.rs

@@ -1042,6 +1042,13 @@ pub struct OutputFilenames {
     crate_stem: String,
     /// Typically based on `.rs` input file name. Any '-' is preserved.
     filestem: String,
+    /// A random string generated per invocation of rustc.
+    ///
+    /// This is prepended to all temporary files so that they do not collide
+    /// during concurrent invocations of rustc, or past invocations that were
+    /// preserved with a flag like `-C save-temps`, since these files may be
+    /// hard-linked.
+    invocation_temp: Option<String>,
     pub single_output_file: Option<OutFileName>,
     temps_directory: Option<PathBuf>,
     pub outputs: OutputTypes,
@@ -1057,13 +1064,15 @@ impl OutputFilenames {
         out_crate_name: String,
         out_filestem: String,
         single_output_file: Option<OutFileName>,
+        invocation_temp: Option<String>,
         temps_directory: Option<PathBuf>,
         extra: String,
         outputs: OutputTypes,
     ) -> Self {
         OutputFilenames {
             out_directory,
             single_output_file,
+            invocation_temp,
             temps_directory,
             outputs,
             crate_stem: format!("{out_crate_name}{extra}"),
@@ -1109,6 +1118,12 @@ impl OutputFilenames {
     pub fn temp_path_ext_for_cgu(&self, ext: &str, codegen_unit_name: &str) -> PathBuf {
         let mut extension = codegen_unit_name.to_string();
 
+        // Append `.{invocation_temp}` to ensure temporary files are unique.
+        if let Some(rng) = &self.invocation_temp {
+            extension.push('.');
+            extension.push_str(rng);
+        }
+
         // FIXME: This is sketchy that we're not appending `.rcgu` when the ext is empty.
         // Append `.rcgu.{ext}`.
         if !ext.is_empty() {

tests/run-make/dirty-incr-due-to-hard-link/rmake.rs

@@ -0,0 +1,25 @@
+//@ only-x86_64-unknown-linux-gnu
+
+use run_make_support::{run, rustc};
+
+fn main() {
+    let mk_rustc = || {
+        let mut rustc = rustc();
+        rustc.input("test.rs").incremental("incr").arg("-Csave-temps").output("test");
+        rustc
+    };
+
+    // Revision 1
+    mk_rustc().cfg("rpass1").run();
+
+    run("test");
+
+    // Revision 2
+    mk_rustc().cfg("cfail2").run_fail();
+    // Expected to fail.
+
+    // Revision 3
+    mk_rustc().cfg("rpass3").run();
+
+    run("test");
+}

tests/run-make/dirty-incr-due-to-hard-link/test.rs

@@ -0,0 +1,31 @@
+#[inline(never)]
+#[cfg(any(rpass1, rpass3))]
+fn a() -> i32 {
+    0
+}
+
+#[cfg(any(cfail2))]
+fn a() -> i32 {
+    1
+}
+
+fn main() {
+    evil::evil();
+    assert_eq!(a(), 0);
+}
+
+mod evil {
+    #[cfg(any(rpass1, rpass3))]
+    pub fn evil() {
+        unsafe {
+            std::arch::asm!("/*  */");
+        }
+    }
+
+    #[cfg(any(cfail2))]
+    pub fn evil() {
+        unsafe {
+            std::arch::asm!("missing");
+        }
+    }
+}