don't show the full linker args unless --verbose is passed

the linker arguments can be *very* long, especially for crates with many dependencies. often they are not useful. omit them unless the user specifically requests them.

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -18,6 +18,7 @@ use rustc_data_structures::temp_dir::MaybeTempDir;
 use rustc_errors::{DiagCtxtHandle, ErrorGuaranteed, FatalError};
 use rustc_fs_util::{fix_windows_verbatim_for_gcc, try_canonicalize};
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
+use rustc_macros::Diagnostic;
 use rustc_metadata::fs::{copy_to_stdout, emit_wrapper_file, METADATA_FILENAME};
 use rustc_metadata::{find_native_static_library, walk_native_lib_search_dirs};
 use rustc_middle::bug;
@@ -984,12 +985,12 @@ fn link_natively(
                 let mut output = prog.stderr.clone();
                 output.extend_from_slice(&prog.stdout);
                 let escaped_output = escape_linker_output(&output, flavor);
-                // FIXME: Add UI tests for this error.
                 let err = errors::LinkingFailed {
                     linker_path: &linker_path,
                     exit_status: prog.status,
                     command: &cmd,
                     escaped_output,
+                    verbose: sess.opts.verbose,
                 };
                 sess.dcx().emit_err(err);
                 // If MSVC's `link.exe` was expected but the return code

compiler/rustc_codegen_ssa/src/errors.rs

@@ -348,6 +348,7 @@ pub struct LinkingFailed<'a> {
     pub exit_status: ExitStatus,
     pub command: &'a Command,
     pub escaped_output: String,
+    pub verbose: bool,
 }
 
 impl<G: EmissionGuarantee> Diagnostic<'_, G> for LinkingFailed<'_> {
@@ -358,7 +359,13 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for LinkingFailed<'_> {
 
         let contains_undefined_ref = self.escaped_output.contains("undefined reference to");
 
-        diag.note(format!("{:?}", self.command)).note(self.escaped_output);
+        if self.verbose {
+            diag.note(format!("{:?}", self.command));
+        } else {
+            diag.note("use `--verbose` to show all linker arguments");
+        }
+
+        diag.note(self.escaped_output);
 
         // Trying to match an error from OS linkers
         // which by now we have no way to translate.

src/tools/run-make-support/src/external_deps/rustc.rs

@@ -316,6 +316,12 @@ impl Rustc {
         self
     }
 
+    /// Pass the `--verbose` flag.
+    pub fn verbose(&mut self) -> &mut Self {
+        self.cmd.arg("--verbose");
+        self
+    }
+
     /// `EXTRARSCXXFLAGS`
     pub fn extra_rs_cxx_flags(&mut self) -> &mut Self {
         // Adapted from tools.mk (trimmed):

tests/run-make/link-args-order/rmake.rs

@@ -15,15 +15,17 @@ fn main() {
         .link_args("b c")
         .link_args("d e")
         .link_arg("f")
+        .arg("--print=link-args")
         .run_fail()
-        .assert_stderr_contains(r#""a" "b" "c" "d" "e" "f""#);
+        .assert_stdout_contains(r#""a" "b" "c" "d" "e" "f""#);
     rustc()
         .input("empty.rs")
         .linker_flavor(linker)
         .arg("-Zpre-link-arg=a")
         .arg("-Zpre-link-args=b c")
         .arg("-Zpre-link-args=d e")
         .arg("-Zpre-link-arg=f")
+        .arg("--print=link-args")
         .run_fail()
-        .assert_stderr_contains(r#""a" "b" "c" "d" "e" "f""#);
+        .assert_stdout_contains(r#""a" "b" "c" "d" "e" "f""#);
 }

tests/run-make/link-dedup/rmake.rs

@@ -14,13 +14,13 @@ fn main() {
     rustc().input("depb.rs").run();
     rustc().input("depc.rs").run();
 
-    let output = rustc().input("empty.rs").cfg("bar").run_fail();
-    output.assert_stderr_contains(needle_from_libs(&["testa", "testb", "testa"]));
+    let output = rustc().input("empty.rs").cfg("bar").arg("--print=link-args").run_fail();
+    output.assert_stdout_contains(needle_from_libs(&["testa", "testb", "testa"]));
 
-    let output = rustc().input("empty.rs").run_fail();
-    output.assert_stderr_contains(needle_from_libs(&["testa"]));
-    output.assert_stderr_not_contains(needle_from_libs(&["testb"]));
-    output.assert_stderr_not_contains(needle_from_libs(&["testa", "testa", "testa"]));
+    let output = rustc().input("empty.rs").arg("--print=link-args").run_fail();
+    output.assert_stdout_contains(needle_from_libs(&["testa"]));
+    output.assert_stdout_not_contains(needle_from_libs(&["testb"]));
+    output.assert_stdout_not_contains(needle_from_libs(&["testa", "testa", "testa"]));
     // Adjacent identical native libraries are no longer deduplicated if
     // they come from different crates (https://github.com/rust-lang/rust/pull/103311)
     // so the following will fail:

tests/run-make/linker-warning/fake-linker.rs

@@ -0,0 +1,13 @@
+fn main() {
+    for arg in std::env::args() {
+        match &*arg {
+            "run_make_info" => println!("foo"),
+            "run_make_warn" => eprintln!("warning: bar"),
+            "run_make_error" => {
+                eprintln!("error: baz");
+                std::process::exit(1);
+            }
+            _ => (),
+        }
+    }
+}

tests/run-make/linker-warning/rmake.rs

@@ -0,0 +1,45 @@
+use std::path::Path;
+
+use run_make_support::rfs::remove_file;
+use run_make_support::{rustc, Rustc};
+
+fn run_rustc() -> Rustc {
+    let mut rustc = rustc();
+    rustc.arg("main.rs").output("main").linker("./fake-linker");
+    rustc
+}
+
+fn main() {
+    // first, compile our linker
+    rustc().arg("fake-linker.rs").output("fake-linker").run();
+
+    // Run rustc with our fake linker, and make sure it shows warnings
+    let warnings = run_rustc().link_arg("run_make_warn").run();
+    warnings.assert_stderr_contains("warning: linker stderr: bar");
+
+    // Make sure it shows stdout, but only when --verbose is passed
+    run_rustc()
+        .link_arg("run_make_info")
+        .verbose()
+        .run()
+        .assert_stderr_contains("warning: linker stdout: foo");
+    run_rustc()
+        .link_arg("run_make_info")
+        .run()
+        .assert_stderr_not_contains("warning: linker stdout: foo");
+
+    // Make sure we short-circuit this new path if the linker exits with an error
+    // (so the diagnostic is less verbose)
+    run_rustc().link_arg("run_make_error").run_fail().assert_stderr_contains("note: error: baz");
+
+    // Make sure we don't show the linker args unless `--verbose` is passed
+    run_rustc()
+        .link_arg("run_make_error")
+        .verbose()
+        .run_fail()
+        .assert_stderr_contains_regex("fake-linker.*run_make_error");
+    run_rustc()
+        .link_arg("run_make_error")
+        .run_fail()
+        .assert_stderr_not_contains_regex("fake-linker.*run_make_error");
+}

tests/run-make/rust-lld/rmake.rs

@@ -14,10 +14,10 @@ fn main() {
     // Opt-in to lld and the self-contained linker, to link with rust-lld. We'll check that by
     // asking the linker to display its version number with a link-arg.
     let output = rustc()
-        .env("RUSTC_LOG", "rustc_codegen_ssa::back::link=info")
         .arg("-Zlinker-features=+lld")
         .arg("-Clink-self-contained=+linker")
         .arg("-Zunstable-options")
+        .arg("--verbose")
         .link_arg(linker_version_flag)
         .input("main.rs")
         .run();
@@ -29,8 +29,8 @@ fn main() {
 
     // It should not be used when we explicitly opt-out of lld.
     let output = rustc()
-        .env("RUSTC_LOG", "rustc_codegen_ssa::back::link=info")
         .link_arg(linker_version_flag)
+        .arg("--verbose")
         .arg("-Zlinker-features=-lld")
         .input("main.rs")
         .run();
@@ -43,8 +43,8 @@ fn main() {
     // While we're here, also check that the last linker feature flag "wins" when passed multiple
     // times to rustc.
     let output = rustc()
-        .env("RUSTC_LOG", "rustc_codegen_ssa::back::link=info")
         .link_arg(linker_version_flag)
+        .arg("--verbose")
         .arg("-Clink-self-contained=+linker")
         .arg("-Zunstable-options")
         .arg("-Zlinker-features=-lld")
@@ -60,6 +60,7 @@ fn main() {
 }
 
 fn find_lld_version_in_logs(stderr: String) -> bool {
-    let lld_version_re = Regex::new(r"^LLD [0-9]+\.[0-9]+\.[0-9]+").unwrap();
+    let lld_version_re =
+        Regex::new(r"^warning: linker stdout: LLD [0-9]+\.[0-9]+\.[0-9]+").unwrap();
     stderr.lines().any(|line| lld_version_re.is_match(line.trim()))
 }