Write to stdout if - is given as output file

If `-o -` or `--emit KIND=-` is provided, output will be written
to stdout instead. Binary output (`obj`, `llvm-bc`, `link` and
`metadata`) being written this way will result in an error unless
stdout is not a tty. Multiple output types going to stdout will
trigger an error too, as they will all be mixded together.

Author: pjhades

Cargo.lock

@@ -3702,6 +3702,7 @@ dependencies = [
 name = "rustc_interface"
 version = "0.0.0"
 dependencies = [
+ "atty",
  "libloading",
  "rustc-rayon",
  "rustc-rayon-core",
@@ -4166,6 +4167,7 @@ dependencies = [
 name = "rustc_session"
 version = "0.0.0"
 dependencies = [
+ "atty",
  "getopts",
  "libc",
  "rustc_ast",

compiler/rustc_codegen_ssa/messages.ftl

@@ -9,6 +9,8 @@ codegen_ssa_archive_build_failure =
 
 codegen_ssa_atomic_compare_exchange = Atomic compare-exchange intrinsic missing failure memory ordering
 
+codegen_ssa_binary_output_to_tty = option `-o` or `--emit` is used to write binary output type `{$shorthand}` to stdout, but stdout is a tty
+
 codegen_ssa_check_installed_visual_studio = please ensure that Visual Studio 2017 or later, or Build Tools for Visual Studio were installed with the Visual C++ option.
 
 codegen_ssa_copy_path = could not copy {$from} to {$to}: {$error}

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -8,7 +8,7 @@ use rustc_errors::{ErrorGuaranteed, Handler};
 use rustc_fs_util::fix_windows_verbatim_for_gcc;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc_metadata::find_native_static_library;
-use rustc_metadata::fs::{emit_wrapper_file, METADATA_FILENAME};
+use rustc_metadata::fs::{copy_to_stdout, emit_wrapper_file, METADATA_FILENAME};
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
 use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::middle::exported_symbols::SymbolExportKind;
@@ -68,6 +68,7 @@ pub fn link_binary<'a>(
 ) -> Result<(), ErrorGuaranteed> {
     let _timer = sess.timer("link_binary");
     let output_metadata = sess.opts.output_types.contains_key(&OutputType::Metadata);
+    let mut tempfiles_for_stdout_output: Vec<PathBuf> = Vec::new();
     for &crate_type in sess.crate_types().iter() {
         // Ignore executable crates if we have -Z no-codegen, as they will error.
         if (sess.opts.unstable_opts.no_codegen || !sess.opts.output_types.should_codegen())
@@ -97,12 +98,15 @@ pub fn link_binary<'a>(
                 .tempdir()
                 .unwrap_or_else(|error| sess.emit_fatal(errors::CreateTempDir { error }));
             let path = MaybeTempDir::new(tmpdir, sess.opts.cg.save_temps);
-            let out_filename = out_filename(
+            let output = out_filename(
                 sess,
                 crate_type,
                 outputs,
                 codegen_results.crate_info.local_crate_name,
             );
+            let crate_name = format!("{}", codegen_results.crate_info.local_crate_name);
+            let out_filename =
+                output.file_for_writing(outputs, OutputType::Exe, Some(crate_name.as_str()));
             match crate_type {
                 CrateType::Rlib => {
                     let _timer = sess.timer("link_rlib");
@@ -152,6 +156,17 @@ pub fn link_binary<'a>(
                     );
                 }
             }
+
+            if output.is_stdout() {
+                if output.is_tty() {
+                    sess.emit_err(errors::BinaryOutputToTty {
+                        shorthand: OutputType::Exe.shorthand(),
+                    });
+                } else if let Err(e) = copy_to_stdout(&out_filename) {
+                    sess.emit_err(errors::CopyPath::new(&out_filename, output.as_path(), e));
+                }
+                tempfiles_for_stdout_output.push(out_filename);
+            }
         }
     }
 
@@ -189,6 +204,11 @@ pub fn link_binary<'a>(
             remove_temps_from_module(allocator_module);
         }
 
+        // Remove the temporary files if output goes to stdout
+        for temp in tempfiles_for_stdout_output {
+            ensure_removed(sess.diagnostic(), &temp);
+        }
+
         // If no requested outputs require linking, then the object temporaries should
         // be kept.
         if !sess.opts.output_types.should_link() {

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -23,12 +23,13 @@ use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc_incremental::{
     copy_cgu_workproduct_to_incr_comp_cache_dir, in_incr_comp_dir, in_incr_comp_dir_sess,
 };
+use rustc_metadata::fs::copy_to_stdout;
 use rustc_metadata::EncodedMetadata;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_middle::middle::exported_symbols::SymbolExportInfo;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::cgu_reuse_tracker::CguReuseTracker;
-use rustc_session::config::{self, CrateType, Lto, OutputFilenames, OutputType};
+use rustc_session::config::{self, CrateType, Lto, OutFileName, OutputFilenames, OutputType};
 use rustc_session::config::{Passes, SwitchWithOptPath};
 use rustc_session::Session;
 use rustc_span::source_map::SourceMap;
@@ -535,9 +536,16 @@ fn produce_final_output_artifacts(
     let mut user_wants_objects = false;
 
     // Produce final compile outputs.
-    let copy_gracefully = |from: &Path, to: &Path| {
-        if let Err(e) = fs::copy(from, to) {
-            sess.emit_err(errors::CopyPath::new(from, to, e));
+    let copy_gracefully = |from: &Path, to: &OutFileName| match to {
+        OutFileName::Stdout => {
+            if let Err(e) = copy_to_stdout(from) {
+                sess.emit_err(errors::CopyPath::new(from, to.as_path(), e));
+            }
+        }
+        OutFileName::Real(path) => {
+            if let Err(e) = fs::copy(from, path) {
+                sess.emit_err(errors::CopyPath::new(from, path, e));
+            }
         }
     };
 
@@ -547,7 +555,12 @@ fn produce_final_output_artifacts(
             //    to copy `foo.0.x` to `foo.x`.
             let module_name = Some(&compiled_modules.modules[0].name[..]);
             let path = crate_output.temp_path(output_type, module_name);
-            copy_gracefully(&path, &crate_output.path(output_type));
+            let output = crate_output.path(output_type);
+            if !output_type.is_text_output() && output.is_tty() {
+                sess.emit_err(errors::BinaryOutputToTty { shorthand: output_type.shorthand() });
+            } else {
+                copy_gracefully(&path, &output);
+            }
             if !sess.opts.cg.save_temps && !keep_numbered {
                 // The user just wants `foo.x`, not `foo.#module-name#.x`.
                 ensure_removed(sess.diagnostic(), &path);

compiler/rustc_codegen_ssa/src/errors.rs

@@ -82,6 +82,12 @@ impl IntoDiagnosticArg for DebugArgPath<'_> {
     }
 }
 
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_binary_output_to_tty)]
+pub struct BinaryOutputToTty {
+    pub shorthand: &'static str,
+}
+
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_ignoring_emit_path)]
 pub struct IgnoringEmitPath {

compiler/rustc_driver_impl/src/lib.rs

@@ -34,7 +34,9 @@ use rustc_interface::{interface, Queries};
 use rustc_lint::LintStore;
 use rustc_metadata::locator;
 use rustc_session::config::{nightly_options, CG_OPTIONS, Z_OPTIONS};
-use rustc_session::config::{ErrorOutputType, Input, OutputType, PrintRequest, TrimmedDefPaths};
+use rustc_session::config::{
+    ErrorOutputType, Input, OutFileName, OutputType, PrintRequest, TrimmedDefPaths,
+};
 use rustc_session::cstore::MetadataLoader;
 use rustc_session::getopts::{self, Matches};
 use rustc_session::lint::{Lint, LintId};
@@ -437,9 +439,12 @@ fn run_compiler(
 }
 
 // Extract output directory and file from matches.
-fn make_output(matches: &getopts::Matches) -> (Option<PathBuf>, Option<PathBuf>) {
+fn make_output(matches: &getopts::Matches) -> (Option<PathBuf>, Option<OutFileName>) {
     let odir = matches.opt_str("out-dir").map(|o| PathBuf::from(&o));
-    let ofile = matches.opt_str("o").map(|o| PathBuf::from(&o));
+    let ofile = matches.opt_str("o").map(|o| match o.as_str() {
+        "-" => OutFileName::Stdout,
+        path => OutFileName::Real(PathBuf::from(path)),
+    });
     (odir, ofile)
 }
 
@@ -685,7 +690,7 @@ fn print_crate_info(
                 for &style in &crate_types {
                     let fname =
                         rustc_session::output::filename_for_input(sess, style, id, &t_outputs);
-                    safe_println!("{}", fname.file_name().unwrap().to_string_lossy());
+                    safe_println!("{}", fname.as_path().file_name().unwrap().to_string_lossy());
                 }
             }
             Cfg => {

compiler/rustc_driver_impl/src/pretty.rs

@@ -9,7 +9,7 @@ use rustc_hir_pretty as pprust_hir;
 use rustc_middle::hir::map as hir_map;
 use rustc_middle::mir::{write_mir_graphviz, write_mir_pretty};
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_session::config::{PpAstTreeMode, PpHirMode, PpMode, PpSourceMode};
+use rustc_session::config::{OutFileName, PpAstTreeMode, PpHirMode, PpMode, PpSourceMode};
 use rustc_session::Session;
 use rustc_span::symbol::Ident;
 use rustc_span::FileName;
@@ -359,8 +359,8 @@ fn get_source(sess: &Session) -> (String, FileName) {
 
 fn write_or_print(out: &str, sess: &Session) {
     match &sess.io.output_file {
-        None => print!("{out}"),
-        Some(p) => {
+        None | Some(OutFileName::Stdout) => print!("{out}"),
+        Some(OutFileName::Real(p)) => {
             if let Err(e) = std::fs::write(p, out) {
                 sess.emit_fatal(UnprettyDumpFail {
                     path: p.display().to_string(),

compiler/rustc_interface/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2021"
 [lib]
 
 [dependencies]
+atty = "0.2.13"
 libloading = "0.7.1"
 tracing = "0.1"
 rustc-rayon-core = { version = "0.5.0", optional = true }

compiler/rustc_interface/messages.ftl

@@ -33,6 +33,7 @@ interface_mixed_proc_macro_crate =
 interface_multiple_output_types_adaption =
     due to multiple output types requested, the explicitly specified output file name will be adapted for each output type
 
+interface_multiple_output_types_to_stdout = can't use option `-o` or `--emit` to write multiple output types to stdout
 interface_out_dir_error =
     failed to find or create the directory specified by `--out-dir`
 

compiler/rustc_interface/src/errors.rs

@@ -108,3 +108,7 @@ pub struct IgnoringExtraFilename;
 #[derive(Diagnostic)]
 #[diag(interface_ignoring_out_dir)]
 pub struct IgnoringOutDir;
+
+#[derive(Diagnostic)]
+#[diag(interface_multiple_output_types_to_stdout)]
+pub struct MultipleOutputTypesToStdout;