metadata-link: add -Zmetadata-link flag

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -45,7 +45,7 @@ pub fn crates_export_threshold(crate_types: &[CrateType]) -> SymbolExportLevel {
 fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<SymbolExportLevel> {
     assert_eq!(cnum, LOCAL_CRATE);
 
-    if !tcx.sess.opts.output_types.should_codegen() {
+    if !tcx.sess.opts.output_types.should_codegen() && !tcx.sess.opts.debugging_opts.metadata_link {
         return Default::default();
     }
 
@@ -164,7 +164,7 @@ fn exported_symbols_provider_local(
 ) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportLevel)] {
     assert_eq!(cnum, LOCAL_CRATE);
 
-    if !tcx.sess.opts.output_types.should_codegen() {
+    if !tcx.sess.opts.output_types.should_codegen() && !tcx.sess.opts.debugging_opts.metadata_link {
         return &[];
     }
 

compiler/rustc_interface/src/tests.rs

@@ -706,6 +706,7 @@ fn test_debugging_options_tracking_hash() {
     tracked!(instrument_mcount, true);
     tracked!(link_only, true);
     tracked!(merge_functions, Some(MergeFunctions::Disabled));
+    tracked!(metadata_link, true);
     tracked!(mir_emit_retag, true);
     tracked!(mir_opt_level, Some(4));
     tracked!(mutable_noalias, Some(true));

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -815,11 +815,14 @@ fn should_encode_stability(def_kind: DefKind) -> bool {
 ///
 /// Return a pair, resp. for CTFE and for LLVM.
 fn should_encode_mir(tcx: TyCtxt<'_>, def_id: LocalDefId) -> (bool, bool) {
+    let always_encode_mir = tcx.sess.opts.debugging_opts.always_encode_mir;
+    let metadata_link = tcx.sess.opts.debugging_opts.metadata_link;
+
     match tcx.def_kind(def_id) {
         // Constructors
         DefKind::Ctor(_, _) => {
-            let mir_opt_base = tcx.sess.opts.output_types.should_codegen()
-                || tcx.sess.opts.debugging_opts.always_encode_mir;
+            let mir_opt_base =
+                tcx.sess.opts.output_types.should_codegen() || always_encode_mir || metadata_link;
             (true, mir_opt_base)
         }
         // Constants
@@ -831,19 +834,17 @@ fn should_encode_mir(tcx: TyCtxt<'_>, def_id: LocalDefId) -> (bool, bool) {
             let generics = tcx.generics_of(def_id);
             let needs_inline = (generics.requires_monomorphization(tcx)
                 || tcx.codegen_fn_attrs(def_id).requests_inline())
-                && tcx.sess.opts.output_types.should_codegen();
+                && (tcx.sess.opts.output_types.should_codegen() || metadata_link);
             // Only check the presence of the `const` modifier.
             let is_const_fn = tcx.is_const_fn_raw(def_id.to_def_id());
-            let always_encode_mir = tcx.sess.opts.debugging_opts.always_encode_mir;
             (is_const_fn, needs_inline || always_encode_mir)
         }
         // Closures can't be const fn.
         DefKind::Closure => {
             let generics = tcx.generics_of(def_id);
             let needs_inline = (generics.requires_monomorphization(tcx)
                 || tcx.codegen_fn_attrs(def_id).requests_inline())
-                && tcx.sess.opts.output_types.should_codegen();
-            let always_encode_mir = tcx.sess.opts.debugging_opts.always_encode_mir;
+                && (tcx.sess.opts.output_types.should_codegen() || metadata_link);
             (false, needs_inline || always_encode_mir)
         }
         // Generators require optimized MIR to compute layout.
@@ -2020,7 +2021,7 @@ impl<'tcx, 'v> ItemLikeVisitor<'v> for ImplVisitor<'tcx> {
 /// Used to prefetch queries which will be needed later by metadata encoding.
 /// Only a subset of the queries are actually prefetched to keep this code smaller.
 fn prefetch_mir(tcx: TyCtxt<'_>) {
-    if !tcx.sess.opts.output_types.should_codegen() {
+    if !tcx.sess.opts.output_types.should_codegen() && !tcx.sess.opts.debugging_opts.metadata_link {
         // We won't emit MIR, so don't prefetch it.
         return;
     }

compiler/rustc_session/src/options.rs

@@ -1121,6 +1121,8 @@ options! {
         the same values as the target option of the same name"),
     meta_stats: bool = (false, parse_bool, [UNTRACKED],
         "gather metadata statistics (default: no)"),
+    metadata_link: bool = (false, parse_bool, [TRACKED],
+        "always emit metadata that's equivalent to metadata,link"),
     mir_emit_retag: bool = (false, parse_bool, [TRACKED],
         "emit Retagging MIR statements, interpreted e.g., by miri; implies -Zmir-opt-level=0 \
         (default: no)"),

src/test/run-make/pipelined/Makefile

@@ -0,0 +1,33 @@
+-include ../../run-make-fulldeps/tools.mk
+
+O=$(TMPDIR)/together
+S=$(TMPDIR)/separate
+
+all: $O/main $S/main
+	# Should produce identical output
+	cmp $O/main	$S/main
+
+# Build with combined --emit metadata,link
+$O/main: $O/libmiddle.rlib $O/libleaf.rlib
+	$(BARE_RUSTC) --out-dir $O main.rs --extern middle=$O/libmiddle.rlib -Ldependency=$O
+	$O/main
+
+$O/libmiddle.rlib: middle.rs $O/libleaf.rmeta
+	$(BARE_RUSTC) --out-dir $O --emit link middle.rs --extern leaf=$O/libleaf.rmeta
+
+$O/libleaf.rlib $O/libleaf.rmeta: leaf.rs
+	$(BARE_RUSTC) --out-dir $O --emit metadata,link leaf.rs
+
+# Build with separate --emit metadata / --emit link
+$S/main: $S/libmiddle.rlib $S/libleaf.rlib
+	$(BARE_RUSTC) --out-dir $S main.rs --extern middle=$S/libmiddle.rlib -Ldependency=$S
+	$S/main
+
+$S/libmiddle.rlib: middle.rs $S/libleaf.rmeta
+	$(BARE_RUSTC) --out-dir $S --emit link middle.rs --extern leaf=$S/libleaf.rmeta
+
+$S/libleaf.rlib: leaf.rs
+	$(BARE_RUSTC) --out-dir $S --emit link leaf.rs
+
+$S/libleaf.rmeta: leaf.rs
+	$(BARE_RUSTC) --out-dir $S --emit metadata -Zmetadata-link leaf.rs

src/test/run-make/pipelined/leaf.rs

@@ -0,0 +1,30 @@
+#![crate_type = "rlib"]
+
+pub static FOO: &str = "this is a static";
+
+#[derive(Debug)]
+pub struct Plain {
+    pub a: u32,
+    pub b: u32,
+}
+
+#[derive(Debug)]
+pub struct GenericStruct<A> {
+    pub a: A,
+    pub b: Option<A>,
+}
+
+pub fn simple(a: u32, b: u32) -> u32 {
+    let c = a + b;
+    println!("simple {} + {} => {}", a, b, c);
+    c
+}
+
+#[inline]
+pub fn inlined(a: u32, b: u32) -> u32 {
+    a * b
+}
+
+pub fn generic<D: std::fmt::Debug>(d: D) {
+    println!("generically printing {:?}", d);
+}

src/test/run-make/pipelined/main.rs

@@ -0,0 +1,10 @@
+#![crate_type = "bin"]
+
+fn main() {
+    middle::do_a_thing();
+
+    println!("middle::BAR {}", middle::BAR);
+
+    assert_eq!(middle::simple(2, 3), 5);
+    assert_eq!(middle::inlined(2, 3), 6);
+}

src/test/run-make/pipelined/middle.rs

@@ -0,0 +1,23 @@
+#![crate_type = "rlib"]
+
+extern crate leaf;
+
+pub static BAR: &str = leaf::FOO;
+
+pub use leaf::simple;
+pub use leaf::inlined;
+
+pub fn do_a_thing() {
+    let s = leaf::GenericStruct {
+        a: "hello",
+        b: Some("world")
+    };
+
+    let u = leaf::GenericStruct {
+        a: leaf::Plain { a: 1, b: 2 },
+        b: None
+    };
+
+    leaf::generic(s);
+    leaf::generic(u);
+}