Use miri inside the target directory used by rustc as Miri's target directory

.github/workflows/ci.yml

@@ -83,6 +83,12 @@ jobs:
             --host ${{ matrix.host_target }}
           rustup default master
 
+      # We need a nightly Cargo to run tests that depend on unstable Cargo features.
+      - name: Install latest nightly
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+
       - name: Show Rust version
         run: |
           rustup show

cargo-miri/bin.rs

@@ -6,7 +6,7 @@ use std::io::{self, BufRead, BufReader, BufWriter, Read, Write};
 use std::iter::TakeWhile;
 use std::ops::Not;
 use std::path::{Path, PathBuf};
-use std::process::Command;
+use std::process::{Command, Stdio};
 
 use serde::{Deserialize, Serialize};
 
@@ -112,40 +112,60 @@ fn has_arg_flag(name: &str) -> bool {
     args.any(|val| val == name)
 }
 
-/// Yields all values of command line flag `name`.
-struct ArgFlagValueIter<'a> {
-    args: TakeWhile<env::Args, fn(&String) -> bool>,
+/// Yields all values of command line flag `name` as `Ok(arg)`, and all other arguments except
+/// the flag as `Err(arg)`.
+struct ArgFlagValueWithOtherArgsIter<'a, I> {
+    args: TakeWhile<I, fn(&String) -> bool>,
     name: &'a str,
 }
 
-impl<'a> ArgFlagValueIter<'a> {
-    fn new(name: &'a str) -> Self {
+impl<'a, I: Iterator<Item = String>> ArgFlagValueWithOtherArgsIter<'a, I> {
+    fn new(args: I, name: &'a str) -> Self {
         Self {
             // Stop searching at `--`.
-            args: env::args().take_while(|val| val != "--"),
+            args: args.take_while(|val| val != "--"),
             name,
         }
     }
 }
 
+impl<I: Iterator<Item = String>> Iterator for ArgFlagValueWithOtherArgsIter<'_, I> {
+    type Item = Result<String, String>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let arg = self.args.next()?;
+        if arg.starts_with(self.name) {
+            // Strip leading `name`.
+            let suffix = &arg[self.name.len()..];
+            if suffix.is_empty() {
+                // This argument is exactly `name`; the next one is the value.
+                return self.args.next().map(Ok);
+            } else if suffix.starts_with('=') {
+                // This argument is `name=value`; get the value.
+                // Strip leading `=`.
+                return Some(Ok(suffix[1..].to_owned()));
+            }
+        }
+        Some(Err(arg))
+    }
+}
+
+/// Yields all values of command line flag `name`.
+struct ArgFlagValueIter<'a>(ArgFlagValueWithOtherArgsIter<'a, env::Args>);
+
+impl<'a> ArgFlagValueIter<'a> {
+    fn new(name: &'a str) -> Self {
+        Self(ArgFlagValueWithOtherArgsIter::new(env::args(), name))
+    }
+}
+
 impl Iterator for ArgFlagValueIter<'_> {
     type Item = String;
 
     fn next(&mut self) -> Option<Self::Item> {
         loop {
-            let arg = self.args.next()?;
-            if !arg.starts_with(self.name) {
-                continue;
-            }
-            // Strip leading `name`.
-            let suffix = &arg[self.name.len()..];
-            if suffix.is_empty() {
-                // This argument is exactly `name`; the next one is the value.
-                return self.args.next();
-            } else if suffix.starts_with('=') {
-                // This argument is `name=value`; get the value.
-                // Strip leading `=`.
-                return Some(suffix[1..].to_owned());
+            if let Ok(value) = self.0.next()? {
+                return Some(value);
             }
         }
     }
@@ -510,8 +530,59 @@ fn phase_cargo_miri(mut args: env::Args) {
         &host
     };
 
-    // Forward all further arguments to cargo.
-    cmd.args(args);
+    let mut target_dir = None;
+
+    // Forward all arguments before `--` other than `--target-dir` and its value to Cargo.
+    for arg in ArgFlagValueWithOtherArgsIter::new(&mut args, "--target-dir") {
+        match arg {
+            Ok(value) => target_dir = Some(value.into()),
+            Err(arg) => drop(cmd.arg(arg)),
+        }
+    }
+
+    // Detect the target directory if it's not specified via `--target-dir`.
+    let target_dir = target_dir.get_or_insert_with(|| {
+        #[derive(Deserialize)]
+        struct Metadata {
+            target_directory: PathBuf,
+        }
+        let mut cmd = cargo();
+        // `-Zunstable-options` is required by `--config`.
+        cmd.args(["metadata", "--no-deps", "--format-version=1", "-Zunstable-options"]);
+        // The `build.target-dir` config can by passed by `--config` flags, so forward them to
+        // `cargo metadata`.
+        let config_flag = "--config";
+        for arg in ArgFlagValueWithOtherArgsIter::new(
+            env::args().skip(3), // skip the program name, "miri" and "run" / "test"
+            config_flag,
+        ) {
+            if let Ok(config) = arg {
+                cmd.arg(config_flag).arg(config);
+            }
+        }
+        let mut child = cmd
+            .stdin(Stdio::null())
+            .stdout(Stdio::piped())
+            .spawn()
+            .expect("failed ro run `cargo metadata`");
+        // Check this `Result` after `status.success()` is checked, so we don't print the error
+        // to stderr if `cargo metadata` is also printing to stderr.
+        let metadata: Result<Metadata, _> = serde_json::from_reader(child.stdout.take().unwrap());
+        let status = child.wait().expect("failed to wait `cargo metadata` to exit");
+        if !status.success() {
+            std::process::exit(status.code().unwrap_or(-1));
+        }
+        metadata
+            .unwrap_or_else(|e| show_error(format!("invalid `cargo metadata` output: {}", e)))
+            .target_directory
+    });
+
+    // Set `--target-dir` to `miri` inside the original target directory.
+    target_dir.push("miri");
+    cmd.arg("--target-dir").arg(target_dir);
+
+    // Forward all further arguments after `--` to cargo.
+    cmd.arg("--").args(args);
 
     // Set `RUSTC_WRAPPER` to ourselves.  Cargo will prepend that binary to its usual invocation,
     // i.e., the first argument is `rustc` -- which is what we use in `main` to distinguish

test-cargo-miri/.gitignore

@@ -1 +1,4 @@
 *.real
+custom-run
+custom-test
+config-cli

test-cargo-miri/run-test.py

@@ -101,6 +101,11 @@ def test_cargo_miri_run():
         "run.subcrate.stdout.ref", "run.subcrate.stderr.ref",
         env={'MIRIFLAGS': "-Zmiri-disable-isolation"},
     )
+    test("`cargo miri run` (custom target dir)",
+        # Attempt to confuse the argument parser.
+        cargo_miri("run") + ["--target-dir=custom-run", "--", "--target-dir=target/custom-run"],
+        "run.args.stdout.ref", "run.custom-target-dir.stderr.ref",
+    )
 
 def test_cargo_miri_test():
     # rustdoc is not run on foreign targets
@@ -144,8 +149,18 @@ def test_cargo_miri_test():
         cargo_miri("test") + ["-p", "subcrate", "--doc"],
         "test.stdout-empty.ref", "test.stderr-proc-macro-doctest.ref",
     )
+    test("`cargo miri test` (custom target dir)",
+        cargo_miri("test") + ["--target-dir=custom-test"],
+        default_ref, "test.stderr-empty.ref",
+    )
+    del os.environ["CARGO_TARGET_DIR"] # this overrides `build.target-dir` passed by `--config`, so unset it
+    test("`cargo miri test` (config-cli)",
+        cargo_miri("test") + ["--config=build.target-dir=\"config-cli\"", "-Zunstable-options"],
+        default_ref, "test.stderr-empty.ref",
+    )
 
 os.chdir(os.path.dirname(os.path.realpath(__file__)))
+os.environ["CARGO_TARGET_DIR"] = "target" # this affects the location of the target directory that we need to check
 os.environ["RUST_TEST_NOCAPTURE"] = "0" # this affects test output, so make sure it is not set
 os.environ["RUST_TEST_THREADS"] = "1" # avoid non-deterministic output due to concurrent test runs
 
@@ -158,6 +173,10 @@ if not 'MIRI_SYSROOT' in os.environ:
     subprocess.run(cargo_miri("setup"), check=True)
 test_cargo_miri_run()
 test_cargo_miri_test()
+for target_dir in ["target", "custom-run", "custom-test", "config-cli"]:
+    if os.listdir(target_dir) != ["miri"]:
+        fail(f"`{target_dir}` contains unexpected files")
+    os.access(os.path.join(target_dir, "miri", "debug", "deps"), os.F_OK)
 
 print("\nTEST SUCCESSFUL!")
 sys.exit(0)

test-cargo-miri/run.custom-target-dir.stderr.ref

@@ -0,0 +1,2 @@
+main
+--target-dir=target/custom-run