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.

7 files changed, 99 insertions, 39 deletions

diff --git a/compiler/rustc_interface/Cargo.toml b/compiler/rustc_interface/Cargo.toml
index 2c7438ed9db..7826d42dcb2 100644
--- a/compiler/rustc_interface/Cargo.toml
+++ b/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 }
diff --git a/compiler/rustc_interface/messages.ftl b/compiler/rustc_interface/messages.ftl
index be1a75f020b..bd9fad8b042 100644
--- a/compiler/rustc_interface/messages.ftl
+++ b/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`
 
diff --git a/compiler/rustc_interface/src/errors.rs b/compiler/rustc_interface/src/errors.rs
index 0eedee25026..a9ab2720d89 100644
--- a/compiler/rustc_interface/src/errors.rs
+++ b/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;
diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 39d56897999..2edc72ba72e 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -14,7 +14,7 @@ use rustc_middle::{bug, ty};
 use rustc_parse::maybe_new_parser_from_source_str;
 use rustc_query_impl::QueryCtxt;
 use rustc_query_system::query::print_query_stack;
-use rustc_session::config::{self, ErrorOutputType, Input, OutputFilenames};
+use rustc_session::config::{self, ErrorOutputType, Input, OutFileName, OutputFilenames};
 use rustc_session::config::{CheckCfg, ExpectedValues};
 use rustc_session::lint;
 use rustc_session::parse::{CrateConfig, ParseSess};
@@ -252,7 +252,7 @@ pub struct Config {
 
     pub input: Input,
     pub output_dir: Option<PathBuf>,
-    pub output_file: Option<PathBuf>,
+    pub output_file: Option<OutFileName>,
     pub file_loader: Option<Box<dyn FileLoader + Send + Sync>>,
     pub locale_resources: &'static [&'static str],
 
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index 42d8d228091..83a74742f5b 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -24,7 +24,7 @@ use rustc_parse::{parse_crate_from_file, parse_crate_from_source_str, validate_a
 use rustc_passes::{self, hir_stats, layout_test};
 use rustc_plugin_impl as plugin;
 use rustc_resolve::Resolver;
-use rustc_session::config::{CrateType, Input, OutputFilenames, OutputType};
+use rustc_session::config::{CrateType, Input, OutFileName, OutputFilenames, OutputType};
 use rustc_session::cstore::{MetadataLoader, Untracked};
 use rustc_session::output::filename_for_input;
 use rustc_session::search_paths::PathKind;
@@ -373,19 +373,23 @@ fn generated_output_paths(
 ) -> Vec<PathBuf> {
     let mut out_filenames = Vec::new();
     for output_type in sess.opts.output_types.keys() {
-        let file = outputs.path(*output_type);
+        let out_filename = outputs.path(*output_type);
+        let file = out_filename.as_path().to_path_buf();
         match *output_type {
             // If the filename has been overridden using `-o`, it will not be modified
             // by appending `.rlib`, `.exe`, etc., so we can skip this transformation.
             OutputType::Exe if !exact_name => {
                 for crate_type in sess.crate_types().iter() {
                     let p = filename_for_input(sess, *crate_type, crate_name, outputs);
-                    out_filenames.push(p);
+                    out_filenames.push(p.as_path().to_path_buf());
                 }
             }
             OutputType::DepInfo if sess.opts.unstable_opts.dep_info_omit_d_target => {
                 // Don't add the dep-info output when omitting it from dep-info targets
             }
+            OutputType::DepInfo if out_filename.is_stdout() => {
+                // Don't add the dep-info output when it goes to stdout
+            }
             _ => {
                 out_filenames.push(file);
             }
@@ -452,7 +456,8 @@ fn write_out_deps(tcx: TyCtxt<'_>, outputs: &OutputFilenames, out_filenames: &[P
     if !sess.opts.output_types.contains_key(&OutputType::DepInfo) {
         return;
     }
-    let deps_filename = outputs.path(OutputType::DepInfo);
+    let deps_output = outputs.path(OutputType::DepInfo);
+    let deps_filename = deps_output.as_path();
 
     let result: io::Result<()> = try {
         // Build a list of files used to compile the output and
@@ -515,33 +520,47 @@ fn write_out_deps(tcx: TyCtxt<'_>, outputs: &OutputFilenames, out_filenames: &[P
             }
         }
 
-        let mut file = BufWriter::new(fs::File::create(&deps_filename)?);
-        for path in out_filenames {
-            writeln!(file, "{}: {}\n", path.display(), files.join(" "))?;
-        }
+        let write_deps_to_file = |file: &mut dyn Write| -> io::Result<()> {
+            for path in out_filenames {
+                writeln!(file, "{}: {}\n", path.display(), files.join(" "))?;
+            }
 
-        // Emit a fake target for each input file to the compilation. This
-        // prevents `make` from spitting out an error if a file is later
-        // deleted. For more info see #28735
-        for path in files {
-            writeln!(file, "{path}:")?;
-        }
+            // Emit a fake target for each input file to the compilation. This
+            // prevents `make` from spitting out an error if a file is later
+            // deleted. For more info see #28735
+            for path in files {
+                writeln!(file, "{path}:")?;
+            }
 
-        // Emit special comments with information about accessed environment variables.
-        let env_depinfo = sess.parse_sess.env_depinfo.borrow();
-        if !env_depinfo.is_empty() {
-            let mut envs: Vec<_> = env_depinfo
-                .iter()
-                .map(|(k, v)| (escape_dep_env(*k), v.map(escape_dep_env)))
-                .collect();
-            envs.sort_unstable();
-            writeln!(file)?;
-            for (k, v) in envs {
-                write!(file, "# env-dep:{k}")?;
-                if let Some(v) = v {
-                    write!(file, "={v}")?;
-                }
+            // Emit special comments with information about accessed environment variables.
+            let env_depinfo = sess.parse_sess.env_depinfo.borrow();
+            if !env_depinfo.is_empty() {
+                let mut envs: Vec<_> = env_depinfo
+                    .iter()
+                    .map(|(k, v)| (escape_dep_env(*k), v.map(escape_dep_env)))
+                    .collect();
+                envs.sort_unstable();
                 writeln!(file)?;
+                for (k, v) in envs {
+                    write!(file, "# env-dep:{k}")?;
+                    if let Some(v) = v {
+                        write!(file, "={v}")?;
+                    }
+                    writeln!(file)?;
+                }
+            }
+
+            Ok(())
+        };
+
+        match deps_output {
+            OutFileName::Stdout => {
+                let mut file = BufWriter::new(io::stdout());
+                write_deps_to_file(&mut file)?;
+            }
+            OutFileName::Real(ref path) => {
+                let mut file = BufWriter::new(fs::File::create(path)?);
+                write_deps_to_file(&mut file)?;
             }
         }
     };
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 28e719a40e5..77ee2b40e37 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -11,7 +11,7 @@ use rustc_session::config::InstrumentXRay;
 use rustc_session::config::TraitSolver;
 use rustc_session::config::{build_configuration, build_session_options, to_crate_config};
 use rustc_session::config::{
-    BranchProtection, Externs, OomStrategy, OutputType, OutputTypes, PAuthKey, PacRet,
+    BranchProtection, Externs, OomStrategy, OutFileName, OutputType, OutputTypes, PAuthKey, PacRet,
     ProcMacroExecutionStrategy, SymbolManglingVersion, WasiExecModel,
 };
 use rustc_session::config::{CFGuard, ExternEntry, LinkerPluginLto, LtoCli, SwitchWithOptPath};
@@ -167,8 +167,14 @@ fn test_output_types_tracking_hash_different_paths() {
     let mut v2 = Options::default();
     let mut v3 = Options::default();
 
-    v1.output_types = OutputTypes::new(&[(OutputType::Exe, Some(PathBuf::from("./some/thing")))]);
-    v2.output_types = OutputTypes::new(&[(OutputType::Exe, Some(PathBuf::from("/some/thing")))]);
+    v1.output_types = OutputTypes::new(&[(
+        OutputType::Exe,
+        Some(OutFileName::Real(PathBuf::from("./some/thing"))),
+    )]);
+    v2.output_types = OutputTypes::new(&[(
+        OutputType::Exe,
+        Some(OutFileName::Real(PathBuf::from("/some/thing"))),
+    )]);
     v3.output_types = OutputTypes::new(&[(OutputType::Exe, None)]);
 
     assert_non_crate_hash_different(&v1, &v2);
@@ -182,13 +188,13 @@ fn test_output_types_tracking_hash_different_construction_order() {
     let mut v2 = Options::default();
 
     v1.output_types = OutputTypes::new(&[
-        (OutputType::Exe, Some(PathBuf::from("./some/thing"))),
-        (OutputType::Bitcode, Some(PathBuf::from("./some/thing.bc"))),
+        (OutputType::Exe, Some(OutFileName::Real(PathBuf::from("./some/thing")))),
+        (OutputType::Bitcode, Some(OutFileName::Real(PathBuf::from("./some/thing.bc")))),
     ]);
 
     v2.output_types = OutputTypes::new(&[
-        (OutputType::Bitcode, Some(PathBuf::from("./some/thing.bc"))),
-        (OutputType::Exe, Some(PathBuf::from("./some/thing"))),
+        (OutputType::Bitcode, Some(OutFileName::Real(PathBuf::from("./some/thing.bc")))),
+        (OutputType::Exe, Some(OutFileName::Real(PathBuf::from("./some/thing")))),
     ]);
 
     assert_same_hash(&v1, &v2);
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index cb19750203e..87252fefb1e 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -11,7 +11,7 @@ use rustc_parse::validate_attr;
 use rustc_session as session;
 use rustc_session::config::CheckCfg;
 use rustc_session::config::{self, CrateType};
-use rustc_session::config::{ErrorOutputType, OutputFilenames};
+use rustc_session::config::{ErrorOutputType, OutFileName, OutputFilenames, OutputTypes};
 use rustc_session::filesearch::sysroot_candidates;
 use rustc_session::lint::{self, BuiltinLintDiagnostics, LintBuffer};
 use rustc_session::parse::CrateConfig;
@@ -500,7 +500,36 @@ pub fn collect_crate_types(session: &Session, attrs: &[ast::Attribute]) -> Vec<C
     base
 }
 
+fn multiple_output_types_to_stdout(
+    output_types: &OutputTypes,
+    single_output_file_is_stdout: bool,
+) -> bool {
+    if atty::is(atty::Stream::Stdout) {
+        // If stdout is a tty, check if multiple text output types are
+        // specified by `--emit foo=- --emit bar=-` or `-o - --emit foo,bar`
+        let named_text_types = output_types
+            .iter()
+            .filter(|(f, o)| f.is_text_output() && *o == &Some(OutFileName::Stdout))
+            .count();
+        let unnamed_text_types =
+            output_types.iter().filter(|(f, o)| f.is_text_output() && o.is_none()).count();
+        named_text_types > 1 || unnamed_text_types > 1 && single_output_file_is_stdout
+    } else {
+        // Otherwise, all the output types should be checked
+        let named_types =
+            output_types.values().filter(|o| *o == &Some(OutFileName::Stdout)).count();
+        let unnamed_types = output_types.values().filter(|o| o.is_none()).count();
+        named_types > 1 || unnamed_types > 1 && single_output_file_is_stdout
+    }
+}
+
 pub fn build_output_filenames(attrs: &[ast::Attribute], sess: &Session) -> OutputFilenames {
+    if multiple_output_types_to_stdout(
+        &sess.opts.output_types,
+        sess.io.output_file == Some(OutFileName::Stdout),
+    ) {
+        sess.emit_fatal(errors::MultipleOutputTypesToStdout);
+    }
     match sess.io.output_file {
         None => {
             // "-" as input file will cause the parser to read from stdin so we
@@ -544,7 +573,7 @@ pub fn build_output_filenames(attrs: &[ast::Attribute], sess: &Session) -> Outpu
 
             OutputFilenames::new(
                 out_file.parent().unwrap_or_else(|| Path::new("")).to_path_buf(),
-                out_file.file_stem().unwrap_or_default().to_str().unwrap().to_string(),
+                out_file.filestem().unwrap_or_default().to_str().unwrap().to_string(),
                 ofile,
                 sess.io.temps_dir.clone(),
                 sess.opts.cg.extra_filename.clone(),