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

the linker arguments can be *very* long, especially for crates with many dependencies. some parts of them are not very useful. unless specifically requested:
- omit object files specific to the current invocation
- fold rlib files into a single braced argument (in shell expansion format)

this shortens the output significantly without removing too much information.

Author: jyn514

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -992,12 +992,12 @@ 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,
+                    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

@@ -1,6 +1,7 @@
 //! Errors emitted by codegen_ssa
 
 use std::borrow::Cow;
+use std::ffi::OsString;
 use std::io::Error;
 use std::num::ParseIntError;
 use std::path::{Path, PathBuf};
@@ -345,21 +346,82 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for ThorinErrorWrapper {
 }
 
 pub(crate) struct LinkingFailed<'a> {
-    pub linker_path: &'a PathBuf,
+    pub linker_path: &'a Path,
     pub exit_status: ExitStatus,
-    pub command: &'a Command,
+    pub command: Command,
     pub escaped_output: String,
+    pub verbose: bool,
 }
 
 impl<G: EmissionGuarantee> Diagnostic<'_, G> for LinkingFailed<'_> {
-    fn into_diag(self, dcx: DiagCtxtHandle<'_>, level: Level) -> Diag<'_, G> {
+    fn into_diag(mut self, dcx: DiagCtxtHandle<'_>, level: Level) -> Diag<'_, G> {
         let mut diag = Diag::new(dcx, level, fluent::codegen_ssa_linking_failed);
         diag.arg("linker_path", format!("{}", self.linker_path.display()));
         diag.arg("exit_status", format!("{}", self.exit_status));
 
         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 {
+            enum ArgGroup {
+                Regular(OsString),
+                Objects(usize),
+                Rlibs(PathBuf, Vec<OsString>),
+            }
+
+            // Omit rust object files and fold rlibs in the error by default to make linker errors a
+            // bit less verbose.
+            let orig_args = self.command.take_args();
+            let mut args: Vec<ArgGroup> = vec![];
+            for arg in orig_args {
+                if arg.as_encoded_bytes().ends_with(b".rcgu.o") {
+                    if let Some(ArgGroup::Objects(n)) = args.last_mut() {
+                        *n += 1;
+                    } else {
+                        args.push(ArgGroup::Objects(1));
+                    }
+                } else if arg.as_encoded_bytes().ends_with(b".rlib") {
+                    let rlib_path = Path::new(&arg);
+                    let dir = rlib_path.parent().unwrap();
+                    let filename = rlib_path.file_name().unwrap().to_owned();
+                    if let Some(ArgGroup::Rlibs(parent, rlibs)) = args.last_mut() {
+                        if parent == dir {
+                            rlibs.push(filename);
+                        } else {
+                            args.push(ArgGroup::Rlibs(dir.to_owned(), vec![filename]));
+                        }
+                    } else {
+                        args.push(ArgGroup::Rlibs(dir.to_owned(), vec![filename]));
+                    }
+                } else {
+                    args.push(ArgGroup::Regular(arg));
+                }
+            }
+            self.command.args(args.into_iter().map(|arg_group| match arg_group {
+                ArgGroup::Regular(arg) => arg,
+                ArgGroup::Objects(n) => OsString::from(format!("<{n} object files omitted>")),
+                ArgGroup::Rlibs(dir, rlibs) => {
+                    let mut arg = dir.into_os_string();
+                    arg.push("/{");
+                    let mut first = true;
+                    for rlib in rlibs {
+                        if !first {
+                            arg.push(",");
+                        }
+                        first = false;
+                        arg.push(rlib);
+                    }
+                    arg.push("}");
+                    arg
+                }
+            }));
+
+            diag.note(format!("{:?}", self.command));
+            diag.note("some arguments are omitted. 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

@@ -325,6 +325,12 @@ 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/main.rs

@@ -0,0 +1 @@
+fn main() {}

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

@@ -0,0 +1,28 @@
+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();
+
+    // 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")
+        .assert_stderr_not_contains("object files omitted")
+        .assert_stderr_contains_regex(r"lib(/|\\\\)libstd");
+    run_rustc()
+        .link_arg("run_make_error")
+        .run_fail()
+        .assert_stderr_contains("fake-linker")
+        .assert_stderr_contains("object files omitted")
+        .assert_stderr_contains_regex(r"\{")
+        .assert_stderr_not_contains_regex(r"lib(/|\\\\)libstd");
+}