Auto merge of #119286 - jyn514:linker-output, r=bjorn3

show linker output even if the linker succeeds

Show stderr and stderr by default, controlled by a new `linker_messages` lint.

fixes https://github.com/rust-lang/rust/issues/83436. fixes https://github.com/rust-lang/rust/issues/38206. cc https://rust-lang.zulipchat.com/#narrow/stream/233931-t-compiler.2Fmajor-changes/topic/uplift.20some.20-Zverbose.20calls.20and.20rename.20to.E2.80.A6.20compiler-team.23706/near/408986134

<!-- try-job: dist-x86_64-msvc -->
try-job: aarch64-apple

r? `@bjorn3`

3 files changed, 20 insertions, 4 deletions

diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index 0d3ab6ad97d..99b033db115 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -1842,12 +1842,19 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         let mut hostflags = flags.clone();
         hostflags.push(format!("-Lnative={}", builder.test_helpers_out(compiler.host).display()));
         hostflags.extend(linker_flags(builder, compiler.host, LldThreads::No));
-        for flag in hostflags {
-            cmd.arg("--host-rustcflags").arg(flag);
-        }
 
         let mut targetflags = flags;
         targetflags.push(format!("-Lnative={}", builder.test_helpers_out(target).display()));
+
+        // FIXME: on macOS, we get linker warnings about duplicate `-lm` flags. We should investigate why this happens.
+        if suite == "ui-fulldeps" && target.ends_with("darwin") {
+            hostflags.push("-Alinker_messages".into());
+            targetflags.push("-Alinker_messages".into());
+        }
+
+        for flag in hostflags {
+            cmd.arg("--host-rustcflags").arg(flag);
+        }
         for flag in targetflags {
             cmd.arg("--target-rustcflags").arg(flag);
         }
@@ -3554,6 +3561,8 @@ impl Step for CodegenGCC {
         let mut cargo = build_cargo();
 
         cargo
+            // cg_gcc's build system ignores RUSTFLAGS. pass some flags through CG_RUSTFLAGS instead.
+            .env("CG_RUSTFLAGS", "-Alinker-messages")
             .arg("--")
             .arg("test")
             .arg("--use-system-gcc")
diff --git a/src/bootstrap/src/core/builder/cargo.rs b/src/bootstrap/src/core/builder/cargo.rs
index 6b792108784..d418237a568 100644
--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -273,6 +273,13 @@ impl Cargo {
             self.rustflags.arg("-Clink-arg=-gz");
         }
 
+        // Ignore linker warnings for now. These are complicated to fix and don't affect the build.
+        // FIXME: we should really investigate these...
+        // cfg(bootstrap)
+        if compiler.stage != 0 {
+            self.rustflags.arg("-Alinker-messages");
+        }
+
         // Throughout the build Cargo can execute a number of build scripts
         // compiling C/C++ code and we need to pass compilers, archivers, flags, etc
         // obtained previously to those build scripts.
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index ad67c2ba245..0437ebb5857 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -178,7 +178,7 @@ pub(crate) fn new_dcx(
             Box::new(
                 JsonEmitter::new(
                     Box::new(io::BufWriter::new(io::stderr())),
-                    source_map,
+                    Some(source_map),
                     fallback_bundle,
                     pretty,
                     json_rendered,