Enable -Zembed-metadata=no by default on nightly Cargo

src/compiler/build_context/target_info.rs

@@ -60,6 +60,9 @@ pub struct TargetInfo {
     pub rustflags: Rc<[String]>,
     /// Extra flags to pass to `rustdoc`, see [`extra_args`].
     pub rustdocflags: Rc<[String]>,
+    /// Should metadata be embedded in .rlib files?
+    /// Corresponds to `-Zembed-metadata`.
+    pub should_embed_metadata: bool,
 }
 
 /// Kind of each file generated by a Unit, part of `FileType`.
@@ -344,6 +347,21 @@ impl TargetInfo {
                 }
             }
 
+            let should_embed_metadata = match gctx.cli_unstable().embed_metadata {
+                Some(v) => v,
+                None => {
+                    let cargo_nightly = matches!(
+                        crate::version().release_channel.as_deref(),
+                        Some("nightly" | "dev")
+                    );
+                    let rustc_nightly = matches!(rustc.version.pre.as_str(), "dev" | "nightly");
+
+                    // Enable -Zembed-metadata=no by default if both cargo and rustc are nightly
+                    let is_nightly = cargo_nightly && rustc_nightly;
+                    !is_nightly
+                }
+            };
+
             return Ok(TargetInfo {
                 crate_type_process,
                 crate_types: RefCell::new(map),
@@ -361,6 +379,7 @@ impl TargetInfo {
                 cfg,
                 supports_std,
                 support_split_debuginfo,
+                should_embed_metadata,
             });
         }
     }
@@ -573,10 +592,9 @@ impl TargetInfo {
         mode: CompileMode,
         target_kind: &TargetKind,
         target_triple: &str,
-        gctx: &GlobalContext,
     ) -> CargoResult<(Vec<FileType>, Vec<CrateType>)> {
         match mode {
-            CompileMode::Build => self.calc_rustc_outputs(target_kind, target_triple, gctx),
+            CompileMode::Build => self.calc_rustc_outputs(target_kind, target_triple),
             CompileMode::Test => {
                 match self.file_types(&CrateType::Bin, FileFlavor::Normal, target_triple)? {
                     Some(fts) => Ok((fts, Vec::new())),
@@ -597,7 +615,6 @@ impl TargetInfo {
         &self,
         target_kind: &TargetKind,
         target_triple: &str,
-        gctx: &GlobalContext,
     ) -> CargoResult<(Vec<FileType>, Vec<CrateType>)> {
         let mut unsupported = Vec::new();
         let mut result = Vec::new();
@@ -619,7 +636,7 @@ impl TargetInfo {
             }
         }
         if !result.is_empty() {
-            if !gctx.should_embed_metadata()
+            if !self.should_embed_metadata()
                 && crate_types
                     .iter()
                     .any(|ct| ct.benefits_from_no_embed_metadata())
@@ -650,6 +667,12 @@ impl TargetInfo {
     pub fn maybe_support_std(&self) -> bool {
         matches!(self.supports_std, Some(true) | None)
     }
+
+    /// Should crate metadata be embedded into .rlib files?
+    /// If not, they will only be stored in .rmeta files.
+    pub fn should_embed_metadata(&self) -> bool {
+        self.should_embed_metadata
+    }
 }
 
 /// Takes rustc output (using specialized command line args), and calculates the file prefix and

src/compiler/build_runner/compilation_files.rs

@@ -420,7 +420,6 @@ impl<'a, 'gctx: 'a> CompilationFiles<'a, 'gctx> {
                 CompileMode::Build,
                 &TargetKind::Bin,
                 bcx.target_data.short_name(&kind),
-                bcx.gctx,
             )
             .expect("target must support `bin`");
 
@@ -664,7 +663,7 @@ impl<'a, 'gctx: 'a> CompilationFiles<'a, 'gctx> {
         let info = bcx.target_data.info(unit.kind);
         let triple = bcx.target_data.short_name(&unit.kind);
         let (file_types, unsupported) =
-            info.rustc_outputs(unit.mode, unit.target.kind(), triple, bcx.gctx)?;
+            info.rustc_outputs(unit.mode, unit.target.kind(), triple)?;
         if file_types.is_empty() {
             if !unsupported.is_empty() {
                 let unsupported_strs: Vec<_> = unsupported.iter().map(|ct| ct.as_str()).collect();

src/compiler/fingerprint/mod.rs

@@ -1675,7 +1675,8 @@ fn calculate_normal(
     // rustc to link to deps using `--extern`. If it changes, we should rebuild everything.
     build_runner
         .bcx
-        .gctx
+        .target_data
+        .info(unit.kind)
         .should_embed_metadata()
         .not()
         .hash(&mut config);

src/compiler/mod.rs

@@ -1320,7 +1320,12 @@ fn build_base_args(
 
     if unit.mode.is_check() {
         cmd.arg("--emit=dep-info,metadata");
-    } else if !build_runner.bcx.gctx.should_embed_metadata() {
+    } else if !build_runner
+        .bcx
+        .target_data
+        .info(unit.kind)
+        .should_embed_metadata()
+    {
         // Nightly rustc supports the -Zembed-metadata=no flag, which tells it to avoid including
         // full metadata in rlib/dylib artifacts, to save space on disk. In this case, metadata
         // will only be stored in .rmeta files.
@@ -1814,7 +1819,11 @@ pub fn extern_args(
     let mut result = Vec::new();
     let deps = build_runner.unit_deps(unit);
 
-    let no_embed_metadata = !build_runner.bcx.gctx.should_embed_metadata();
+    let no_embed_metadata = !build_runner
+        .bcx
+        .target_data
+        .info(unit.kind)
+        .should_embed_metadata();
     let public_dependency_enabled = is_public_dependency_enabled(build_runner, unit);
 
     // Closure to add one dependency to `result`.

src/context/mod.rs

@@ -1269,10 +1269,6 @@ impl GlobalContext {
         self.extra_verbose
     }
 
-    pub fn should_embed_metadata(&self) -> bool {
-        self.cli_unstable().embed_metadata.unwrap_or(true)
-    }
-
     pub fn network_allowed(&self) -> bool {
         !self.offline_flag().is_some()
     }

src/ops/cargo_clean.rs

@@ -300,7 +300,7 @@ fn clean_specs(
                         let triple = target_data.short_name(compile_kind);
                         let (file_types, _unsupported) = target_data
                             .info(*compile_kind)
-                            .rustc_outputs(mode, target.kind(), triple, clean_ctx.gctx)?;
+                            .rustc_outputs(mode, target.kind(), triple)?;
                         let artifact_dir = layout
                             .artifact_dir()
                             .expect("artifact-dir was not locked during clean");
@@ -377,7 +377,7 @@ fn clean_specs(
                         let triple = target_data.short_name(compile_kind);
                         let (file_types, _unsupported) = target_data
                             .info(*compile_kind)
-                            .rustc_outputs(mode, target.kind(), triple, clean_ctx.gctx)?;
+                            .rustc_outputs(mode, target.kind(), triple)?;
                         let artifact_dir = layout
                             .artifact_dir()
                             .expect("artifact-dir was not locked during clean");

tests/testsuite/build.rs

@@ -6549,7 +6549,7 @@ fn embed_metadata_no_invalidate() {
 
 "#]])
         .run();
-    p.cargo("build")
+    p.cargo("build -Z embed-metadata=yes")
         .masquerade_as_nightly_cargo(&["-Z embed-metadata"])
         .with_stderr_data(str![[r#"
 [COMPILING] bar v0.5.0 ([ROOT]/foo/bar)