Auto merge of rust-lang#119286 - jyn514:linker-output, r=<try>

show linker output even if the linker succeeds

- show stderr by default
- show stdout if `--verbose` is passed
- remove both from RUSTC_LOG
- hide the linker cli args unless `--verbose` is passed

fixes rust-lang#83436. fixes rust-lang#38206. fixes rust-lang#109979. helps with rust-lang#46998. 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

this is based on rust-lang#119129 for convenience so i didn't have to duplicate the changes around saving `--verbose` in rust-lang@cb6d033#diff-7a49efa20548d6806dbe1c66dd4dc445fda18fcbbf1709520cadecc4841aae12

try-job: aarch64-apple

r? `@bjorn3`

Author: bors

compiler/rustc_codegen_ssa/messages.ftl

@@ -183,6 +183,8 @@ codegen_ssa_linker_file_stem = couldn't extract file stem from specified linker
 codegen_ssa_linker_not_found = linker `{$linker_path}` not found
     .note = {$error}
 
+codegen_ssa_linker_output = {$inner}
+
 codegen_ssa_linker_unsupported_modifier = `as-needed` modifier not supported for current linker
 
 codegen_ssa_linking_failed = linking with `{$linker_path}` failed: {$exit_status}

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -15,12 +15,14 @@ use rustc_ast::CRATE_NODE_ID;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::temp_dir::MaybeTempDir;
-use rustc_errors::{DiagCtxtHandle, ErrorGuaranteed, FatalError};
+use rustc_errors::{DiagCtxtHandle, ErrorGuaranteed, FatalError, LintDiagnostic};
 use rustc_fs_util::{fix_windows_verbatim_for_gcc, try_canonicalize};
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
+use rustc_macros::LintDiagnostic;
 use rustc_metadata::fs::{METADATA_FILENAME, copy_to_stdout, emit_wrapper_file};
 use rustc_metadata::{find_native_static_library, walk_native_lib_search_dirs};
 use rustc_middle::bug;
+use rustc_middle::lint::lint_level;
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
 use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::middle::exported_symbols::SymbolExportKind;
@@ -29,6 +31,7 @@ use rustc_session::config::{
     OutputType, PrintKind, SplitDwarfKind, Strip,
 };
 use rustc_session::cstore::DllImport;
+use rustc_session::lint::builtin::LINKER_MESSAGES;
 use rustc_session::output::{check_file_is_writeable, invalid_output_for_target, out_filename};
 use rustc_session::search_paths::PathKind;
 use rustc_session::utils::NativeLibKind;
@@ -762,6 +765,14 @@ fn link_dwarf_object(sess: &Session, cg_results: &CodegenResults, executable_out
     }
 }
 
+#[derive(LintDiagnostic)]
+#[diag(codegen_ssa_linker_output)]
+/// Translating this is kind of useless. We don't pass translation flags to the linker, so we'd just
+/// end up with inconsistent languages within the same diagnostic.
+struct LinkerOutput {
+    inner: String,
+}
+
 /// Create a dynamic library or executable.
 ///
 /// This will invoke the system linker/cc to create the resulting file. This links to all upstream
@@ -998,12 +1009,12 @@ 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
@@ -1045,8 +1056,27 @@ fn link_natively(
 
                 sess.dcx().abort_if_errors();
             }
-            info!("linker stderr:\n{}", escape_string(&prog.stderr));
-            info!("linker stdout:\n{}", escape_string(&prog.stdout));
+
+            let (level, src) = codegen_results.crate_info.lint_levels.linker_messages;
+            let lint = |msg| {
+                lint_level(sess, LINKER_MESSAGES, level, src, None, |diag| {
+                    LinkerOutput { inner: msg }.decorate_lint(diag)
+                })
+            };
+
+            if !prog.stderr.is_empty() {
+                // We already print `warning:` at the start of the diagnostic. Remove it from the linker output if present.
+                let stderr = escape_string(&prog.stderr);
+                debug!("original stderr: {stderr}");
+                let stderr = stderr
+                    .strip_prefix("warning: ")
+                    .unwrap_or(&stderr)
+                    .replace(": warning: ", ": ");
+                lint(format!("linker stderr: {stderr}"));
+            }
+            if !prog.stdout.is_empty() && sess.opts.verbose {
+                lint(format!("linker stdout: {}", escape_string(&prog.stdout)))
+            }
         }
         Err(e) => {
             let linker_not_found = e.kind() == io::ErrorKind::NotFound;

compiler/rustc_codegen_ssa/src/base.rs

@@ -45,7 +45,8 @@ use crate::mir::operand::OperandValue;
 use crate::mir::place::PlaceRef;
 use crate::traits::*;
 use crate::{
-    CachedModuleCodegen, CompiledModule, CrateInfo, ModuleCodegen, ModuleKind, errors, meth, mir,
+    CachedModuleCodegen, CodegenLintLevels, CompiledModule, CrateInfo, ModuleCodegen, ModuleKind,
+    errors, meth, mir,
 };
 
 pub(crate) fn bin_op_to_icmp_predicate(op: BinOp, signed: bool) -> IntPredicate {
@@ -926,6 +927,7 @@ impl CrateInfo {
             dependency_formats: Lrc::clone(tcx.dependency_formats(())),
             windows_subsystem,
             natvis_debugger_visualizers: Default::default(),
+            lint_levels: CodegenLintLevels::from_tcx(tcx),
         };
 
         info.native_libraries.reserve(n_crates);

compiler/rustc_codegen_ssa/src/errors.rs

@@ -349,6 +349,7 @@ pub(crate) 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<'_> {
@@ -359,7 +360,13 @@ 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.

compiler/rustc_codegen_ssa/src/lib.rs

@@ -29,18 +29,23 @@ use rustc_ast as ast;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::unord::UnordMap;
+use rustc_hir::CRATE_HIR_ID;
 use rustc_hir::def_id::CrateNum;
 use rustc_macros::{Decodable, Encodable, HashStable};
 use rustc_middle::dep_graph::WorkProduct;
+use rustc_middle::lint::LintLevelSource;
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
 use rustc_middle::middle::dependency_format::Dependencies;
 use rustc_middle::middle::exported_symbols::SymbolExportKind;
+use rustc_middle::ty::TyCtxt;
 use rustc_middle::util::Providers;
 use rustc_serialize::opaque::{FileEncoder, MemDecoder};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use rustc_session::Session;
 use rustc_session::config::{CrateType, OutputFilenames, OutputType, RUST_CGU_EXT};
 use rustc_session::cstore::{self, CrateSource};
+use rustc_session::lint::Level;
+use rustc_session::lint::builtin::LINKER_MESSAGES;
 use rustc_session::utils::NativeLibKind;
 use rustc_span::symbol::Symbol;
 
@@ -200,6 +205,7 @@ pub struct CrateInfo {
     pub dependency_formats: Lrc<Dependencies>,
     pub windows_subsystem: Option<String>,
     pub natvis_debugger_visualizers: BTreeSet<DebuggerVisualizerFile>,
+    pub lint_levels: CodegenLintLevels,
 }
 
 #[derive(Encodable, Decodable)]
@@ -302,3 +308,19 @@ impl CodegenResults {
         Ok((codegen_results, outputs))
     }
 }
+
+/// A list of lint levels used in codegen.
+///
+/// When using `-Z link-only`, we don't have access to the tcx and must work
+/// solely from the `.rlink` file. `Lint`s are defined too early to be encodeable.
+/// Instead, encode exactly the information we need.
+#[derive(Copy, Clone, Debug, Encodable, Decodable)]
+pub struct CodegenLintLevels {
+    linker_messages: (Level, LintLevelSource),
+}
+
+impl CodegenLintLevels {
+    pub fn from_tcx(tcx: TyCtxt<'_>) -> Self {
+        Self { linker_messages: tcx.lint_level_at_node(LINKER_MESSAGES, CRATE_HIR_ID) }
+    }
+}

compiler/rustc_lint/src/levels.rs

@@ -130,12 +130,17 @@ fn lints_that_dont_need_to_run(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LintId> {
             !has_future_breakage && !lint.eval_always
         })
         .filter_map(|lint| {
-            let lint_level = map.lint_level_id_at_node(tcx, LintId::of(lint), CRATE_HIR_ID);
-            if matches!(lint_level, (Level::Allow, ..))
-                || (matches!(lint_level, (.., LintLevelSource::Default)))
-                    && lint.default_level(tcx.sess.edition()) == Level::Allow
-            {
-                Some(LintId::of(lint))
+            if !lint.eval_always {
+                let lint_level =
+                    map.lint_level_id_at_node(Some(tcx), tcx.sess, LintId::of(lint), CRATE_HIR_ID);
+                if matches!(lint_level, (Level::Allow, ..))
+                    || (matches!(lint_level, (.., LintLevelSource::Default)))
+                        && lint.default_level(tcx.sess.edition()) == Level::Allow
+                {
+                    Some(LintId::of(lint))
+                } else {
+                    None
+                }
             } else {
                 None
             }
@@ -248,8 +253,8 @@ impl LintLevelsProvider for LintLevelQueryMap<'_> {
     fn insert(&mut self, id: LintId, lvl: LevelAndSource) {
         self.specs.specs.get_mut_or_insert_default(self.cur.local_id).insert(id, lvl);
     }
-    fn get_lint_level(&self, lint: &'static Lint, _: &Session) -> LevelAndSource {
-        self.specs.lint_level_id_at_node(self.tcx, LintId::of(lint), self.cur)
+    fn get_lint_level(&self, lint: &'static Lint, sess: &Session) -> LevelAndSource {
+        self.specs.lint_level_id_at_node(Some(self.tcx), sess, LintId::of(lint), self.cur)
     }
     fn push_expectation(&mut self, id: LintExpectationId, expectation: LintExpectation) {
         self.specs.expectations.push((id, expectation))

compiler/rustc_lint_defs/src/builtin.rs

@@ -60,6 +60,7 @@ declare_lint_pass! {
         LARGE_ASSIGNMENTS,
         LATE_BOUND_LIFETIME_ARGUMENTS,
         LEGACY_DERIVE_HELPERS,
+        LINKER_MESSAGES,
         LONG_RUNNING_CONST_EVAL,
         LOSSY_PROVENANCE_CASTS,
         MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
@@ -4080,6 +4081,39 @@ declare_lint! {
     "call to foreign functions or function pointers with FFI-unwind ABI"
 }
 
+declare_lint! {
+    /// The `linker_messages` lint forwards warnings from the linker.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,ignore (needs CLI args, platform-specific)
+    /// extern "C" {
+    ///   fn foo();
+    /// }
+    /// fn main () { unsafe { foo(); } }
+    /// ```
+    ///
+    /// On Linux, using `gcc -Wl,--warn-unresolved-symbols` as a linker, this will produce
+    ///
+    /// ```text
+    /// warning: linker stderr: rust-lld: undefined symbol: foo
+    ///          >>> referenced by rust_out.69edbd30df4ae57d-cgu.0
+    ///          >>>               rust_out.rust_out.69edbd30df4ae57d-cgu.0.rcgu.o:(rust_out::main::h3a90094b06757803)
+    ///   |
+    ///   = note: `#[warn(linker_messages)]` on by default
+    ///
+    /// warning: 1 warning emitted
+    /// ```
+    ///
+    /// ### Explanation
+    ///
+    /// Linkers emit platform-specific and program-specific warnings that cannot be predicted in advance by the rust compiler.
+    /// They are forwarded by default, but can be disabled by adding `#![allow(linker_messages)]` at the crate root.
+    pub LINKER_MESSAGES,
+    Warn,
+    "warnings emitted at runtime by the target-specific linker program"
+}
+
 declare_lint! {
     /// The `named_arguments_used_positionally` lint detects cases where named arguments are only
     /// used positionally in format strings. This usage is valid but potentially very confusing.

compiler/rustc_lint_defs/src/lib.rs

@@ -161,7 +161,19 @@ impl<HCX: rustc_hir::HashStableContext> ToStableHashKey<HCX> for LintExpectation
 /// Setting for how to handle a lint.
 ///
 /// See: <https://doc.rust-lang.org/rustc/lints/levels.html>
-#[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash, HashStable_Generic)]
+#[derive(
+    Clone,
+    Copy,
+    PartialEq,
+    PartialOrd,
+    Eq,
+    Ord,
+    Debug,
+    Hash,
+    Encodable,
+    Decodable,
+    HashStable_Generic
+)]
 pub enum Level {
     /// The `allow` level will not issue any message.
     Allow,

compiler/rustc_middle/src/lint.rs

@@ -3,8 +3,8 @@ use std::cmp;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sorted_map::SortedMap;
 use rustc_errors::{Diag, MultiSpan};
-use rustc_hir::{HirId, ItemLocalId};
-use rustc_macros::HashStable;
+use rustc_hir::{CRATE_HIR_ID, HirId, ItemLocalId};
+use rustc_macros::{Decodable, Encodable, HashStable};
 use rustc_session::Session;
 use rustc_session::lint::builtin::{self, FORBIDDEN_LINT_GROUPS};
 use rustc_session::lint::{FutureIncompatibilityReason, Level, Lint, LintExpectationId, LintId};
@@ -15,7 +15,7 @@ use tracing::instrument;
 use crate::ty::TyCtxt;
 
 /// How a lint level was set.
-#[derive(Clone, Copy, PartialEq, Eq, HashStable, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, HashStable, Debug)]
 pub enum LintLevelSource {
     /// Lint is at the default level as declared in rustc.
     Default,
@@ -119,7 +119,7 @@ impl ShallowLintLevelMap {
     #[instrument(level = "trace", skip(self, tcx), ret)]
     fn probe_for_lint_level(
         &self,
-        tcx: TyCtxt<'_>,
+        tcx: Option<TyCtxt<'_>>,
         id: LintId,
         start: HirId,
     ) -> (Option<Level>, LintLevelSource) {
@@ -132,31 +132,38 @@ impl ShallowLintLevelMap {
         let mut owner = start.owner;
         let mut specs = &self.specs;
 
-        for parent in tcx.hir().parent_id_iter(start) {
-            if parent.owner != owner {
-                owner = parent.owner;
-                specs = &tcx.shallow_lint_levels_on(owner).specs;
-            }
-            if let Some(map) = specs.get(&parent.local_id)
-                && let Some(&(level, src)) = map.get(&id)
-            {
-                return (Some(level), src);
+        if let Some(tcx) = tcx {
+            for parent in tcx.hir().parent_id_iter(start) {
+                if parent.owner != owner {
+                    owner = parent.owner;
+                    specs = &tcx.shallow_lint_levels_on(owner).specs;
+                }
+                if let Some(map) = specs.get(&parent.local_id)
+                    && let Some(&(level, src)) = map.get(&id)
+                {
+                    return (Some(level), src);
+                }
             }
         }
 
         (None, LintLevelSource::Default)
     }
 
     /// Fetch and return the user-visible lint level for the given lint at the given HirId.
-    #[instrument(level = "trace", skip(self, tcx), ret)]
+    #[instrument(level = "trace", skip(self, tcx, sess), ret)]
     pub fn lint_level_id_at_node(
         &self,
-        tcx: TyCtxt<'_>,
+        tcx: Option<TyCtxt<'_>>,
+        sess: &Session,
         lint: LintId,
         cur: HirId,
     ) -> (Level, LintLevelSource) {
+        assert!(
+            tcx.is_some() || cur == CRATE_HIR_ID,
+            "must pass in a tcx to access any level other than the root"
+        );
         let (level, mut src) = self.probe_for_lint_level(tcx, lint, cur);
-        let level = reveal_actual_level(level, &mut src, tcx.sess, lint, |lint| {
+        let level = reveal_actual_level(level, &mut src, sess, lint, |lint| {
             self.probe_for_lint_level(tcx, lint, cur)
         });
         (level, src)
@@ -166,14 +173,19 @@ impl ShallowLintLevelMap {
 impl TyCtxt<'_> {
     /// Fetch and return the user-visible lint level for the given lint at the given HirId.
     pub fn lint_level_at_node(self, lint: &'static Lint, id: HirId) -> (Level, LintLevelSource) {
-        self.shallow_lint_levels_on(id.owner).lint_level_id_at_node(self, LintId::of(lint), id)
+        self.shallow_lint_levels_on(id.owner).lint_level_id_at_node(
+            Some(self),
+            self.sess,
+            LintId::of(lint),
+            id,
+        )
     }
 }
 
 /// This struct represents a lint expectation and holds all required information
 /// to emit the `unfulfilled_lint_expectations` lint if it is unfulfilled after
 /// the `LateLintPass` has completed.
-#[derive(Clone, Debug, HashStable)]
+#[derive(Clone, Debug, Encodable, Decodable, HashStable)]
 pub struct LintExpectation {
     /// The reason for this expectation that can optionally be added as part of
     /// the attribute. It will be displayed as part of the lint message.

compiler/rustc_passes/messages.ftl

@@ -798,6 +798,9 @@ passes_unused_duplicate =
 passes_unused_empty_lints_note =
     attribute `{$name}` with an empty list has no effect
 
+passes_unused_linker_warnings_note =
+    the `linker_warnings` lint can only be controlled at the root of a crate with `--crate-type bin`
+
 passes_unused_multiple =
     multiple `{$name}` attributes
     .suggestion = remove this attribute

compiler/rustc_passes/src/check_attr.rs

@@ -2271,6 +2271,16 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             && item.path == sym::reason
         {
             errors::UnusedNote::NoLints { name: attr.name_or_empty() }
+        } else if matches!(
+            attr.name_or_empty(),
+            sym::allow | sym::warn | sym::deny | sym::forbid | sym::expect
+        ) && let Some(meta) = attr.meta_item_list()
+            && meta.iter().any(|meta| {
+                meta.meta_item().map_or(false, |item| item.path == sym::linker_messages)
+            })
+            && hir_id != CRATE_HIR_ID
+        {
+            errors::UnusedNote::LinkerWarningsBinaryCrateOnly
         } else if attr.name_or_empty() == sym::default_method_body_is_const {
             errors::UnusedNote::DefaultMethodBodyConst
         } else {

compiler/rustc_passes/src/errors.rs

@@ -762,6 +762,8 @@ pub(crate) enum UnusedNote {
     NoLints { name: Symbol },
     #[note(passes_unused_default_method_body_const_note)]
     DefaultMethodBodyConst,
+    #[note(passes_unused_linker_warnings_note)]
+    LinkerWarningsBinaryCrateOnly,
 }
 
 #[derive(LintDiagnostic)]

compiler/rustc_span/src/symbol.rs

@@ -1153,6 +1153,7 @@ symbols! {
         link_section,
         linkage,
         linker,
+        linker_messages,
         lint_reasons,
         literal,
         load,

src/bootstrap/src/core/build_steps/compile.rs

@@ -592,6 +592,11 @@ pub fn std_cargo(builder: &Builder<'_>, target: TargetSelection, stage: u32, car
     // separate setting for the compiler.
     cargo.rustflag("-Cforce-frame-pointers=yes");
 
+    // Ignore linker warnings on macOS for now. These are complicated to fix and don't affect the build.
+    if target.contains("apple-darwin") {
+        cargo.rustflag("-Alinker-messages");
+    }
+
     let html_root =
         format!("-Zcrate-attr=doc(html_root_url=\"{}/\")", builder.doc_rust_lang_org_channel(),);
     cargo.rustflag(&html_root);

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

@@ -319,6 +319,12 @@ 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/fake-linker.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+code=0
+while ! [ $# = 0 ]; do
+    case "$1" in
+        run_make_info) echo "foo"
+            ;;
+        run_make_warn) echo "warning: bar" >&2
+            ;;
+        run_make_error) echo "error: baz" >&2; code=1
+            ;;
+        *) ;;   # rustc passes lots of args we don't care about
+    esac
+    shift
+done
+
+exit $code

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

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

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-by-default-nightly/rmake.rs

@@ -12,24 +12,16 @@ use run_make_support::rustc;
 fn main() {
     // A regular compilation should use rust-lld by default. 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")
-        .link_arg("-Wl,-v")
-        .input("main.rs")
-        .run();
+    let output = rustc().verbose().link_arg("-Wl,-v").input("main.rs").run();
     assert!(
         find_lld_version_in_logs(output.stderr_utf8()),
         "the LLD version string should be present in the output logs:\n{}",
         output.stderr_utf8()
     );
 
     // But it can still be disabled by turning the linker feature off.
-    let output = rustc()
-        .env("RUSTC_LOG", "rustc_codegen_ssa::back::link=info")
-        .link_arg("-Wl,-v")
-        .arg("-Zlinker-features=-lld")
-        .input("main.rs")
-        .run();
+    let output =
+        rustc().verbose().link_arg("-Wl,-v").arg("-Zlinker-features=-lld").input("main.rs").run();
     assert!(
         !find_lld_version_in_logs(output.stderr_utf8()),
         "the LLD version string should not be present in the output logs:\n{}",
@@ -38,6 +30,7 @@ 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()))
 }

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

@@ -15,7 +15,7 @@ fn main() {
     // Compile to a custom target spec with rust-lld enabled by default. 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")
+        .verbose()
         .crate_type("cdylib")
         .target("custom-target.json")
         .link_arg("-Wl,-v")
@@ -44,6 +44,7 @@ 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()))
 }

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")
+        .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)
+        .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)
+        .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()))
 }