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.

2 files changed, 12 insertions, 7 deletions

diff --git a/compiler/rustc_driver_impl/src/lib.rs b/compiler/rustc_driver_impl/src/lib.rs
index 40aa69e5a41..416603a0e1c 100644
--- a/compiler/rustc_driver_impl/src/lib.rs
+++ b/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 => {
diff --git a/compiler/rustc_driver_impl/src/pretty.rs b/compiler/rustc_driver_impl/src/pretty.rs
index ee64b18d3f6..24a5f4030b8 100644
--- a/compiler/rustc_driver_impl/src/pretty.rs
+++ b/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(),