show linker output even if the linker succeeds

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;
+use rustc_errors::{DiagCtxtHandle, 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;
@@ -749,6 +752,14 @@ 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
@@ -981,6 +992,11 @@ fn link_natively(
 
     match prog {
         Ok(prog) => {
+            let is_msvc_link_exe = sess.target.is_like_msvc
+                && flavor == LinkerFlavor::Msvc(Lld::No)
+                // Match exactly "link.exe"
+                && linker_path.to_str() == Some("link.exe");
+
             if !prog.status.success() {
                 let mut output = prog.stderr.clone();
                 output.extend_from_slice(&prog.stdout);
@@ -997,16 +1013,9 @@ fn link_natively(
                 // is not a Microsoft LNK error then suggest a way to fix or
                 // install the Visual Studio build tools.
                 if let Some(code) = prog.status.code() {
-                    if sess.target.is_like_msvc
-                        && flavor == LinkerFlavor::Msvc(Lld::No)
-                        // Respect the command line override
-                        && sess.opts.cg.linker.is_none()
-                        // Match exactly "link.exe"
-                        && linker_path.to_str() == Some("link.exe")
-                        // All Microsoft `link.exe` linking error codes are
-                        // four digit numbers in the range 1000 to 9999 inclusive
-                        && (code < 1000 || code > 9999)
-                    {
+                    // All Microsoft `link.exe` linking ror codes are
+                    // four digit numbers in the range 1000 to 9999 inclusive
+                    if is_msvc_link_exe && (code < 1000 || code > 9999) {
                         let is_vs_installed = windows_registry::find_vs_version().is_ok();
                         let has_linker =
                             windows_registry::find_tool(&sess.target.arch, "link.exe").is_some();
@@ -1028,8 +1037,49 @@ 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 stderr = escape_string(&prog.stderr);
+            let mut stdout = escape_string(&prog.stdout);
+            info!("linker stderr:\n{}", &stderr);
+            info!("linker stdout:\n{}", &stdout);
+
+            // Hide some progress messages from link.exe that we don't care about.
+            // See https://github.com/chromium/chromium/blob/bfa41e41145ffc85f041384280caf2949bb7bd72/build/toolchain/win/tool_wrapper.py#L144-L146
+            if is_msvc_link_exe {
+                if let Ok(str) = str::from_utf8(&prog.stdout) {
+                    let mut output = String::with_capacity(str.len());
+                    for line in stdout.lines() {
+                        if line.starts_with("   Creating library")
+                            || line.starts_with("Generating code")
+                            || line.starts_with("Finished generating code")
+                        {
+                            continue;
+                        }
+                        output += line;
+                        output += "\r\n"
+                    }
+                    stdout = escape_string(output.trim().as_bytes())
+                }
+            }
+
+            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 = stderr
+                    .strip_prefix("warning: ")
+                    .unwrap_or(&stderr)
+                    .replace(": warning: ", ": ");
+                lint(format!("linker stderr: {stderr}"));
+            }
+            if !stdout.is_empty() {
+                lint(format!("linker stdout: {}", stdout))
+            }
         }
         Err(e) => {
             let linker_not_found = e.kind() == io::ErrorKind::NotFound;

compiler/rustc_codegen_ssa/src/base.rs

@@ -44,7 +44,8 @@ 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 {
@@ -927,6 +928,7 @@ 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/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;
 
@@ -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_errors/src/json.rs

@@ -21,7 +21,7 @@ use rustc_error_messages::FluentArgs;
 use rustc_lint_defs::Applicability;
 use rustc_span::Span;
 use rustc_span::hygiene::ExpnData;
-use rustc_span::source_map::SourceMap;
+use rustc_span::source_map::{FilePathMapping, SourceMap};
 use serde::Serialize;
 use termcolor::{ColorSpec, WriteColor};
 
@@ -45,7 +45,7 @@ pub struct JsonEmitter {
     #[setters(skip)]
     dst: IntoDynSyncSend<Box<dyn Write + Send>>,
     #[setters(skip)]
-    sm: Lrc<SourceMap>,
+    sm: Option<Lrc<SourceMap>>,
     fluent_bundle: Option<Lrc<FluentBundle>>,
     #[setters(skip)]
     fallback_bundle: LazyFallbackBundle,
@@ -65,7 +65,7 @@ pub struct JsonEmitter {
 impl JsonEmitter {
     pub fn new(
         dst: Box<dyn Write + Send>,
-        sm: Lrc<SourceMap>,
+        sm: Option<Lrc<SourceMap>>,
         fallback_bundle: LazyFallbackBundle,
         pretty: bool,
         json_rendered: HumanReadableErrorType,
@@ -171,7 +171,7 @@ impl Emitter for JsonEmitter {
     }
 
     fn source_map(&self) -> Option<&SourceMap> {
-        Some(&self.sm)
+        self.sm.as_deref()
     }
 
     fn should_show_explain(&self) -> bool {
@@ -371,7 +371,7 @@ impl Diagnostic {
         }
         HumanEmitter::new(dst, Lrc::clone(&je.fallback_bundle))
             .short_message(short)
-            .sm(Some(Lrc::clone(&je.sm)))
+            .sm(je.sm.clone())
             .fluent_bundle(je.fluent_bundle.clone())
             .diagnostic_width(je.diagnostic_width)
             .macro_backtrace(je.macro_backtrace)
@@ -458,23 +458,34 @@ impl DiagnosticSpan {
         mut backtrace: impl Iterator<Item = ExpnData>,
         je: &JsonEmitter,
     ) -> DiagnosticSpan {
-        let start = je.sm.lookup_char_pos(span.lo());
+        let empty_source_map;
+        let sm = match &je.sm {
+            Some(s) => s,
+            None => {
+                span = rustc_span::DUMMY_SP;
+                empty_source_map = Arc::new(SourceMap::new(FilePathMapping::empty()));
+                empty_source_map
+                    .new_source_file(std::path::PathBuf::from("empty.rs").into(), String::new());
+                &empty_source_map
+            }
+        };
+        let start = sm.lookup_char_pos(span.lo());
         // If this goes from the start of a line to the end and the replacement
         // is an empty string, increase the length to include the newline so we don't
         // leave an empty line
         if start.col.0 == 0
             && let Some((suggestion, _)) = suggestion
             && suggestion.is_empty()
-            && let Ok(after) = je.sm.span_to_next_source(span)
+            && let Ok(after) = sm.span_to_next_source(span)
             && after.starts_with('\n')
         {
             span = span.with_hi(span.hi() + rustc_span::BytePos(1));
         }
-        let end = je.sm.lookup_char_pos(span.hi());
+        let end = sm.lookup_char_pos(span.hi());
         let backtrace_step = backtrace.next().map(|bt| {
             let call_site = Self::from_span_full(bt.call_site, false, None, None, backtrace, je);
             let def_site_span = Self::from_span_full(
-                je.sm.guess_head_span(bt.def_site),
+                sm.guess_head_span(bt.def_site),
                 false,
                 None,
                 None,
@@ -489,7 +500,7 @@ impl DiagnosticSpan {
         });
 
         DiagnosticSpan {
-            file_name: je.sm.filename_for_diagnostics(&start.file.name).to_string(),
+            file_name: sm.filename_for_diagnostics(&start.file.name).to_string(),
             byte_start: start.file.original_relative_byte_pos(span.lo()).0,
             byte_end: start.file.original_relative_byte_pos(span.hi()).0,
             line_start: start.line,
@@ -559,19 +570,20 @@ impl DiagnosticSpanLine {
     /// `span` within the line.
     fn from_span(span: Span, je: &JsonEmitter) -> Vec<DiagnosticSpanLine> {
         je.sm
-            .span_to_lines(span)
-            .map(|lines| {
+            .as_ref()
+            .and_then(|sm| {
+                let lines = sm.span_to_lines(span).ok()?;
                 // We can't get any lines if the source is unavailable.
                 if !should_show_source_code(
                     &je.ignored_directories_in_source_blocks,
-                    &je.sm,
+                    &sm,
                     &lines.file,
                 ) {
-                    return vec![];
+                    return None;
                 }
 
                 let sf = &*lines.file;
-                lines
+                let span_lines = lines
                     .lines
                     .iter()
                     .map(|line| {
@@ -582,8 +594,9 @@ impl DiagnosticSpanLine {
                             line.end_col.0 + 1,
                         )
                     })
-                    .collect()
+                    .collect();
+                Some(span_lines)
             })
-            .unwrap_or_else(|_| vec![])
+            .unwrap_or_default()
     }
 }

compiler/rustc_errors/src/json/tests.rs

@@ -47,7 +47,7 @@ fn test_positions(code: &str, span: (u32, u32), expected_output: SpanTestData) {
         let output = Arc::new(Mutex::new(Vec::new()));
         let je = JsonEmitter::new(
             Box::new(Shared { data: output.clone() }),
-            sm,
+            Some(sm),
             fallback_bundle,
             true, // pretty
             HumanReadableErrorType::Short,

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,
@@ -4085,6 +4086,39 @@ 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.