[stable] 1.52.1 release

RELEASES.md

@@ -1,3 +1,24 @@
+Version 1.52.1 (2021-05-10)
+============================
+
+This release disables incremental compilation, unless the user has explicitly
+opted in via the newly added RUSTC_FORCE_INCREMENTAL=1 environment variable.
+
+This is due to the widespread, and frequently occuring, breakage encountered by
+Rust users due to newly enabled incremental verification in 1.52.0. Notably,
+Rust users **should** upgrade to 1.52.0 or 1.52.1: the bugs that are detected by
+newly added incremental verification are still present in past stable versions,
+and are not yet fixed on any channel. These bugs can lead to miscompilation of
+Rust binaries.
+
+These problems only affect incremental builds, so release builds with Cargo
+should not be affected unless the user has explicitly opted into incremental.
+Debug and check builds are affected.
+
+See [84970] for more details.
+
+[84970]: https://github.com/rust-lang/rust/issues/84970
+
 Version 1.52.0 (2021-05-06)
 ============================
 

compiler/rustc_query_system/src/query/plumbing.rs

@@ -590,7 +590,19 @@ fn incremental_verify_ich<CTX, K, V: Debug>(
 
     let old_hash = tcx.dep_graph().fingerprint_of(dep_node_index);
 
-    assert!(new_hash == old_hash, "found unstable fingerprints for {:?}: {:?}", dep_node, result);
+    if new_hash != old_hash {
+        let run_cmd = if let Some(crate_name) = &tcx.sess().opts.crate_name {
+            format!("`cargo clean -p {}` or `cargo clean`", crate_name)
+        } else {
+            "`cargo clean`".to_string()
+        };
+        tcx.sess().struct_err(&format!("internal compiler error: encountered incremental compilation error with {:?}", dep_node))
+            .help(&format!("This is a known issue with the compiler. Run {} to allow your project to compile", run_cmd))
+            .note(&format!("Please follow the instructions below to create a bug report with the provided information"))
+            .note(&format!("See <https://github.com/rust-lang/rust/issues/84970> for more information."))
+            .emit();
+        panic!("Found unstable fingerprints for {:?}: {:?}", dep_node, result);
+    }
 }
 
 fn force_query_with_job<C, CTX>(

compiler/rustc_session/src/config.rs

@@ -1885,7 +1885,12 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
 
     check_thread_count(&debugging_opts, error_format);
 
-    let incremental = cg.incremental.as_ref().map(PathBuf::from);
+    let incremental =
+        if std::env::var_os("RUSTC_FORCE_INCREMENTAL").map(|v| v == "1").unwrap_or(false) {
+            cg.incremental.as_ref().map(PathBuf::from)
+        } else {
+            None
+        };
 
     if debugging_opts.profile && incremental.is_some() {
         early_error(

src/doc/rustc/src/codegen-options/index.md

@@ -161,6 +161,9 @@ to save information after compiling a crate to be reused when recompiling the
 crate, improving re-compile times. This takes a path to a directory where
 incremental files will be stored.
 
+Note that this option currently does not take effect unless
+`RUSTC_FORCE_INCREMENTAL=1` in the environment.
+
 ## inline-threshold
 
 This option lets you set the default threshold for inlining a function. It

src/tools/compiletest/src/runtest.rs

@@ -229,7 +229,15 @@ pub fn run(config: Config, testpaths: &TestPaths, revision: Option<&str>) {
         print!("\n\n");
     }
     debug!("running {:?}", testpaths.file.display());
-    let props = TestProps::from_file(&testpaths.file, revision, &config);
+    let mut props = TestProps::from_file(&testpaths.file, revision, &config);
+
+    // Currently, incremental is soft disabled unless this environment
+    // variable is set. A bunch of our tests assume it's enabled, though - so
+    // just enable it for our tests.
+    //
+    // This is deemed preferable to ignoring those tests; we still want to test
+    // incremental somewhat, as users can opt in to it.
+    props.rustc_env.push((String::from("RUSTC_FORCE_INCREMENTAL"), String::from("1")));
 
     let cx = TestCx { config: &config, props: &props, testpaths, revision };
     create_dir_all(&cx.output_base_dir()).unwrap();
@@ -240,7 +248,11 @@ pub fn run(config: Config, testpaths: &TestPaths, revision: Option<&str>) {
         assert!(!props.revisions.is_empty(), "Incremental tests require revisions.");
         cx.init_incremental_test();
         for revision in &props.revisions {
-            let revision_props = TestProps::from_file(&testpaths.file, Some(revision), &config);
+            let mut revision_props = TestProps::from_file(&testpaths.file, Some(revision), &config);
+            // See above - need to enable it explicitly for now.
+            revision_props
+                .rustc_env
+                .push((String::from("RUSTC_FORCE_INCREMENTAL"), String::from("1")));
             let rev_cx = TestCx {
                 config: &config,
                 props: &revision_props,

src/version

@@ -1 +1 @@
-1.52.0
+1.52.1