cargo-miri: use rustc to determine the output filename

Author: RalfJung

cargo-miri/src/phases.rs

@@ -236,18 +236,34 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
         is_bin || is_test
     }
 
-    fn out_filename(prefix: &str, suffix: &str) -> PathBuf {
+    fn out_filename() -> PathBuf {
         if let Some(out_dir) = get_arg_flag_value("--out-dir") {
             let mut path = PathBuf::from(out_dir);
-            path.push(format!(
-                "{}{}{}{}",
-                prefix,
-                get_arg_flag_value("--crate-name").unwrap(),
-                // This is technically a `-C` flag but the prefix seems unique enough...
-                // (and cargo passes this before the filename so it should be unique)
-                get_arg_flag_value("extra-filename").unwrap_or_default(),
-                suffix,
-            ));
+            // Ask rustc for the filename (since that is target-dependent).
+            let mut rustc = miri_for_host(); // sysroot doesn't matter for this so we just use the host
+            rustc.arg("--print").arg("file-names");
+            for flag in ["--crate-name", "--crate-type", "--target"] {
+                if let Some(val) = get_arg_flag_value(flag) {
+                    rustc.arg(flag).arg(val);
+                }
+            }
+            // This is technically passed as `-C extra-filename=...`, but the prefix seems unique
+            // enough... (and cargo passes this before the filename so it should be unique)
+            if let Some(extra) = get_arg_flag_value("extra-filename") {
+                rustc.arg("-C").arg(format!("extra-filename={extra}"));
+            }
+            rustc.arg("-");
+
+            let output = rustc.output().expect("cannot run rustc to determine file name");
+            assert!(
+                output.status.success(),
+                "rustc failed when determining file name:\n{output:?}"
+            );
+            let output =
+                String::from_utf8(output.stdout).expect("rustc returned non-UTF-8 filename");
+            let output = output.lines().next().unwrap();
+
+            path.push(output);
             path
         } else {
             let out_file = get_arg_flag_value("-o").unwrap();
@@ -267,24 +283,27 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
     let info_query = get_arg_flag_value("--print").is_some() || has_arg_flag("-vV");
 
     let store_json = |info: CrateRunInfo| {
-        // Create a stub .d file to stop Cargo from "rebuilding" the crate:
-        // https://github.com/rust-lang/miri/issues/1724#issuecomment-787115693
-        // As we store a JSON file instead of building the crate here, an empty file is fine.
-        let dep_info_name = out_filename("", ".d");
-        if verbose > 0 {
-            eprintln!("[cargo-miri rustc] writing stub dep-info to `{}`", dep_info_name.display());
+        if get_arg_flag_value("--emit").unwrap_or_default().split(',').any(|e| e == "dep-info") {
+            // Create a stub .d file to stop Cargo from "rebuilding" the crate:
+            // https://github.com/rust-lang/miri/issues/1724#issuecomment-787115693
+            // As we store a JSON file instead of building the crate here, an empty file is fine.
+            let dep_info_name = format!(
+                "{}/{}{}.d",
+                get_arg_flag_value("--out-dir").unwrap(),
+                get_arg_flag_value("--crate-name").unwrap(),
+                get_arg_flag_value("extra-filename").unwrap_or_default(),
+            );
+            if verbose > 0 {
+                eprintln!("[cargo-miri rustc] writing stub dep-info to `{dep_info_name}`");
+            }
+            File::create(dep_info_name).expect("failed to create fake .d file");
         }
-        File::create(dep_info_name).expect("failed to create fake .d file");
 
-        let filename = out_filename("", "");
+        let filename = out_filename();
         if verbose > 0 {
             eprintln!("[cargo-miri rustc] writing run info to `{}`", filename.display());
         }
         info.store(&filename);
-        // For Windows and WASM, do the same thing again with `.exe`/`.wasm` appended to the filename.
-        // (Need to do this here as cargo moves that "binary" to a different place before running it.)
-        info.store(&out_filename("", ".exe"));
-        info.store(&out_filename("", ".wasm"));
     };
 
     let runnable_crate = !info_query && is_runnable_crate();
@@ -340,7 +359,7 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
                 eprintln!("[cargo-miri rustc inside rustdoc] going to run:\n{cmd:?}");
             }
 
-            exec_with_pipe(cmd, &env.stdin, format!("{}.stdin", out_filename("", "").display()));
+            exec_with_pipe(cmd, &env.stdin, format!("{}.stdin", out_filename().display()));
         }
 
         return;
@@ -422,15 +441,7 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
     // Create a stub .rlib file if "link" was requested by cargo.
     // This is necessary to prevent cargo from doing rebuilds all the time.
     if emit_link_hack {
-        // Some platforms prepend "lib", some do not... let's just create both files.
-        File::create(out_filename("lib", ".rlib")).expect("failed to create fake .rlib file");
-        File::create(out_filename("", ".rlib")).expect("failed to create fake .rlib file");
-        // Just in case this is a cdylib or staticlib, also create those fake files.
-        File::create(out_filename("lib", ".so")).expect("failed to create fake .so file");
-        File::create(out_filename("lib", ".a")).expect("failed to create fake .a file");
-        File::create(out_filename("lib", ".dylib")).expect("failed to create fake .dylib file");
-        File::create(out_filename("", ".dll")).expect("failed to create fake .dll file");
-        File::create(out_filename("", ".lib")).expect("failed to create fake .lib file");
+        File::create(out_filename()).expect("failed to create fake .rlib file");
     }
 
     debug_cmd("[cargo-miri rustc]", verbose, &cmd);