Avoid writing empty metadata reference file when -Zsplit-metadata is disabled

Author: bjorn3

compiler/rustc_metadata/src/fs.rs

@@ -3,7 +3,7 @@ use std::{fs, io};
 
 use rustc_data_structures::temp_dir::MaybeTempDir;
 use rustc_middle::ty::TyCtxt;
-use rustc_session::config::{OutFileName, OutputType};
+use rustc_session::config::{CrateType, OutFileName, OutputType};
 use rustc_session::output::filename_for_metadata;
 use rustc_session::{MetadataKind, Session};
 use tempfile::Builder as TempFileBuilder;
@@ -51,7 +51,13 @@ pub fn encode_and_write_metadata(tcx: TyCtxt<'_>) -> (EncodedMetadata, bool) {
         .unwrap_or_else(|err| tcx.dcx().emit_fatal(FailedCreateTempdir { err }));
     let metadata_tmpdir = MaybeTempDir::new(metadata_tmpdir, tcx.sess.opts.cg.save_temps);
     let metadata_filename = metadata_tmpdir.as_ref().join("full.rmeta");
-    let metadata_reference_filename = metadata_tmpdir.as_ref().join("ref.rmeta");
+    let metadata_reference_filename = if tcx.sess.opts.unstable_opts.split_metadata
+        && !tcx.crate_types().contains(&CrateType::ProcMacro)
+    {
+        Some(metadata_tmpdir.as_ref().join("ref.rmeta"))
+    } else {
+        None
+    };
 
     // Always create a file at `metadata_filename`, even if we have nothing to write to it.
     // This simplifies the creation of the output `out_filename` when requested.
@@ -61,12 +67,14 @@ pub fn encode_and_write_metadata(tcx: TyCtxt<'_>) -> (EncodedMetadata, bool) {
             std::fs::File::create(&metadata_filename).unwrap_or_else(|err| {
                 tcx.dcx().emit_fatal(FailedCreateFile { filename: &metadata_filename, err });
             });
-            std::fs::File::create(&metadata_reference_filename).unwrap_or_else(|err| {
-                tcx.dcx().emit_fatal(FailedCreateFile { filename: &metadata_filename, err });
-            });
+            if let Some(metadata_reference_filename) = &metadata_reference_filename {
+                std::fs::File::create(metadata_reference_filename).unwrap_or_else(|err| {
+                    tcx.dcx().emit_fatal(FailedCreateFile { filename: &metadata_filename, err });
+                });
+            }
         }
         MetadataKind::Uncompressed | MetadataKind::Compressed => {
-            encode_metadata(tcx, &metadata_filename, &metadata_reference_filename)
+            encode_metadata(tcx, &metadata_filename, metadata_reference_filename.as_deref())
         }
     };
 

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -33,7 +33,7 @@ use rustc_span::{
 };
 use tracing::{debug, instrument, trace};
 
-use crate::errors::{FailCreateFileEncoder, FailWriteFile, FailedCreateFile};
+use crate::errors::{FailCreateFileEncoder, FailWriteFile};
 use crate::rmeta::*;
 
 pub(super) struct EncodeContext<'a, 'tcx> {
@@ -2240,7 +2240,7 @@ impl EncodedMetadata {
     #[inline]
     pub fn from_path(
         path: PathBuf,
-        reference_path: PathBuf,
+        reference_path: Option<PathBuf>,
         temp_dir: Option<MaybeTempDir>,
     ) -> std::io::Result<Self> {
         let file = std::fs::File::open(&path)?;
@@ -2250,8 +2250,11 @@ impl EncodedMetadata {
         }
         let full_mmap = unsafe { Some(Mmap::map(file)?) };
 
-        let reference = std::fs::read(reference_path)?;
-        let reference = if reference.is_empty() { None } else { Some(reference) };
+        let reference = if let Some(reference_path) = reference_path {
+            Some(std::fs::read(reference_path)?)
+        } else {
+            None
+        };
 
         Ok(Self { full_mmap, reference, _temp_dir: temp_dir })
     }
@@ -2296,7 +2299,7 @@ impl<D: Decoder> Decodable<D> for EncodedMetadata {
     }
 }
 
-pub fn encode_metadata(tcx: TyCtxt<'_>, path: &Path, ref_path: &Path) {
+pub fn encode_metadata(tcx: TyCtxt<'_>, path: &Path, ref_path: Option<&Path>) {
     let _prof_timer = tcx.prof.verbose_generic_activity("generate_crate_metadata");
 
     // Since encoding metadata is not in a query, and nothing is cached,
@@ -2327,9 +2330,7 @@ pub fn encode_metadata(tcx: TyCtxt<'_>, path: &Path, ref_path: &Path) {
         root.position.get()
     });
 
-    if tcx.sess.opts.unstable_opts.split_metadata
-        && !tcx.crate_types().contains(&CrateType::ProcMacro)
-    {
+    if let Some(ref_path) = ref_path {
         with_encode_metadata_header(tcx, ref_path, |ecx| {
             let header: LazyValue<CrateHeader> = ecx.lazy(CrateHeader {
                 name: tcx.crate_name(LOCAL_CRATE),
@@ -2340,10 +2341,6 @@ pub fn encode_metadata(tcx: TyCtxt<'_>, path: &Path, ref_path: &Path) {
             });
             header.position.get()
         });
-    } else {
-        std::fs::File::create(&ref_path).unwrap_or_else(|err| {
-            tcx.dcx().emit_fatal(FailedCreateFile { filename: &ref_path, err });
-        });
     }
 }