Only depend on CFG_VERSION in rustc_interface

this avoids having to rebuild the whole compiler on each commit when
`omit-git-hash = false`.

compiler/rustc_incremental/src/persist/file_format.rs

@@ -14,6 +14,7 @@ use rustc_data_structures::memmap::Mmap;
 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
 use rustc_serialize::Encoder;
 use rustc_session::Session;
+use std::borrow::Cow;
 use std::env;
 use std::fs;
 use std::io::{self, Read};
@@ -25,17 +26,12 @@ const FILE_MAGIC: &[u8] = b"RSIC";
 /// Change this if the header format changes.
 const HEADER_FORMAT_VERSION: u16 = 0;
 
-/// A version string that hopefully is always different for compiler versions
-/// with different encodings of incremental compilation artifacts. Contains
-/// the Git commit hash.
-const RUSTC_VERSION: Option<&str> = option_env!("CFG_VERSION");
-
-pub(crate) fn write_file_header(stream: &mut FileEncoder, nightly_build: bool) {
+pub(crate) fn write_file_header(stream: &mut FileEncoder, sess: &Session) {
     stream.emit_raw_bytes(FILE_MAGIC);
     stream
         .emit_raw_bytes(&[(HEADER_FORMAT_VERSION >> 0) as u8, (HEADER_FORMAT_VERSION >> 8) as u8]);
 
-    let rustc_version = rustc_version(nightly_build);
+    let rustc_version = rustc_version(sess.is_nightly_build(), sess.cfg_version);
     assert_eq!(rustc_version.len(), (rustc_version.len() as u8) as usize);
     stream.emit_raw_bytes(&[rustc_version.len() as u8]);
     stream.emit_raw_bytes(rustc_version.as_bytes());
@@ -73,7 +69,7 @@ where
         }
     };
 
-    write_file_header(&mut encoder, sess.is_nightly_build());
+    write_file_header(&mut encoder, sess);
 
     match encode(encoder) {
         Ok(position) => {
@@ -100,9 +96,10 @@ where
 /// - Returns `Err(..)` if some kind of IO error occurred while reading the
 ///   file.
 pub fn read_file(
-    report_incremental_info: bool,
     path: &Path,
-    nightly_build: bool,
+    report_incremental_info: bool,
+    is_nightly_build: bool,
+    cfg_version: &'static str,
 ) -> io::Result<Option<(Mmap, usize)>> {
     let file = match fs::File::open(path) {
         Ok(file) => file,
@@ -152,7 +149,7 @@ pub fn read_file(
         let mut buffer = vec![0; rustc_version_str_len];
         file.read_exact(&mut buffer)?;
 
-        if buffer != rustc_version(nightly_build).as_bytes() {
+        if buffer != rustc_version(is_nightly_build, cfg_version).as_bytes() {
             report_format_mismatch(report_incremental_info, path, "Different compiler version");
             return Ok(None);
         }
@@ -174,17 +171,15 @@ fn report_format_mismatch(report_incremental_info: bool, file: &Path, message: &
     }
 }
 
-fn rustc_version(nightly_build: bool) -> String {
+/// A version string that hopefully is always different for compiler versions
+/// with different encodings of incremental compilation artifacts. Contains
+/// the Git commit hash.
+fn rustc_version(nightly_build: bool, cfg_version: &'static str) -> Cow<'static, str> {
     if nightly_build {
-        if let Some(val) = env::var_os("RUSTC_FORCE_RUSTC_VERSION") {
-            return val.to_string_lossy().into_owned();
+        if let Ok(val) = env::var("RUSTC_FORCE_RUSTC_VERSION") {
+            return val.into();
         }
     }
 
-    RUSTC_VERSION
-        .expect(
-            "Cannot use rustc without explicit version for \
-                          incremental compilation",
-        )
-        .to_string()
+    cfg_version.into()
 }

compiler/rustc_incremental/src/persist/load.rs

@@ -73,12 +73,22 @@ impl<T: Default> LoadResult<T> {
     }
 }
 
-fn load_data(
-    report_incremental_info: bool,
+fn load_data(path: &Path, sess: &Session) -> LoadResult<(Mmap, usize)> {
+    load_data_no_sess(
+        path,
+        sess.opts.unstable_opts.incremental_info,
+        sess.is_nightly_build(),
+        sess.cfg_version,
+    )
+}
+
+fn load_data_no_sess(
     path: &Path,
-    nightly_build: bool,
+    report_incremental_info: bool,
+    is_nightly_build: bool,
+    cfg_version: &'static str,
 ) -> LoadResult<(Mmap, usize)> {
-    match file_format::read_file(report_incremental_info, path, nightly_build) {
+    match file_format::read_file(path, report_incremental_info, is_nightly_build, cfg_version) {
         Ok(Some(data_and_pos)) => LoadResult::Ok { data: data_and_pos },
         Ok(None) => {
             // The file either didn't exist or was produced by an incompatible
@@ -138,14 +148,13 @@ pub fn load_dep_graph(sess: &Session) -> DepGraphFuture {
     let expected_hash = sess.opts.dep_tracking_hash(false);
 
     let mut prev_work_products = FxHashMap::default();
-    let nightly_build = sess.is_nightly_build();
 
     // If we are only building with -Zquery-dep-graph but without an actual
     // incr. comp. session directory, we skip this. Otherwise we'd fail
     // when trying to load work products.
     if sess.incr_comp_session_dir_opt().is_some() {
         let work_products_path = work_products_path(sess);
-        let load_result = load_data(report_incremental_info, &work_products_path, nightly_build);
+        let load_result = load_data(&work_products_path, sess);
 
         if let LoadResult::Ok { data: (work_products_data, start_pos) } = load_result {
             // Decode the list of work_products
@@ -173,10 +182,13 @@ pub fn load_dep_graph(sess: &Session) -> DepGraphFuture {
         }
     }
 
+    let is_nightly_build = sess.is_nightly_build();
+    let cfg_version = sess.cfg_version;
+
     MaybeAsync::Async(std::thread::spawn(move || {
         let _prof_timer = prof.generic_activity("incr_comp_load_dep_graph");
 
-        match load_data(report_incremental_info, &path, nightly_build) {
+        match load_data_no_sess(&path, report_incremental_info, is_nightly_build, cfg_version) {
             LoadResult::DataOutOfDate => LoadResult::DataOutOfDate,
             LoadResult::LoadDepGraph(path, err) => LoadResult::LoadDepGraph(path, err),
             LoadResult::DecodeIncrCache(err) => LoadResult::DecodeIncrCache(err),
@@ -218,11 +230,7 @@ pub fn load_query_result_cache(sess: &Session) -> Option<OnDiskCache<'_>> {
 
     let _prof_timer = sess.prof.generic_activity("incr_comp_load_query_result_cache");
 
-    match load_data(
-        sess.opts.unstable_opts.incremental_info,
-        &query_cache_path(sess),
-        sess.is_nightly_build(),
-    ) {
+    match load_data(&query_cache_path(sess), sess) {
         LoadResult::Ok { data: (bytes, start_pos) } => {
             Some(OnDiskCache::new(sess, bytes, start_pos))
         }

compiler/rustc_incremental/src/persist/save.rs

@@ -164,7 +164,7 @@ pub fn build_dep_graph(
         }
     };
 
-    file_format::write_file_header(&mut encoder, sess.is_nightly_build());
+    file_format::write_file_header(&mut encoder, sess);
 
     // First encode the commandline arguments hash
     sess.opts.dep_tracking_hash(false).encode(&mut encoder);