do not auto-detect the targets in the sysroot, instead specify target manually through env var

.travis.yml

@@ -29,6 +29,12 @@ before_script:
   else
     export MIRI_SYSROOT_BASE=~/.cache/miri/
   fi
+- |
+  if [[ "$TRAVIS_OS_NAME" == osx ]]; then
+    FOREIGN_TARGET=i686-apple-darwin
+  else
+    FOREIGN_TARGET=i686-unknown-linux-gnu
+  fi
 # install Rust
 - curl https://build.travis-ci.org/files/rustup-init.sh -sSf | sh -s -- -y --default-toolchain "$RUST_TOOLCHAIN"
 - export PATH=$HOME/.cargo/bin:$PATH
@@ -43,15 +49,11 @@ script:
 - |
   # Get ourselves a MIR-full libstd for the host and a foreign architecture
   cargo miri setup &&
-  if [[ "$TRAVIS_OS_NAME" == osx ]]; then
-    cargo miri setup --target i686-apple-darwin
-  else
-    cargo miri setup --target i686-unknown-linux-gnu
-  fi
+  cargo miri setup --target "$FOREIGN_TARGET"
 - |
   # Test miri with full MIR, on the host and other architectures
   MIRI_SYSROOT=$MIRI_SYSROOT_BASE/HOST cargo test --release --all-features &&
-  MIRI_SYSROOT=$MIRI_SYSROOT_BASE cargo test --release --all-features
+  MIRI_SYSROOT=$MIRI_SYSROOT_BASE MIRI_TARGET=$FOREIGN_TARGET cargo test --release --all-features
 - |
   # Test cargo integration
   (cd test-cargo-miri && MIRI_SYSROOT=$MIRI_SYSROOT_BASE/HOST ./run-test.py)

README.md

@@ -154,9 +154,9 @@ MIRI_LOG=rustc_mir::interpret=debug,miri::stacked_borrows cargo run tests/run-pa
 In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
 evaluation error was originally created.
 
-### Miri `-Z` flags
+### Miri `-Z` flags and environment variables
 
-Several `-Z` flags are relevant for miri:
+Several `-Z` flags are relevant for Miri:
 
 * `-Zmir-opt-level` controls how many MIR optimizations are performed.  miri
   overrides the default to be `0`; be advised that using any higher level can
@@ -168,6 +168,14 @@ Several `-Z` flags are relevant for miri:
   enforcing the validity invariant, which is enforced by default.  This is
   mostly useful for debugging; it means miri will miss bugs in your program.
 
+Moreover, Miri recognizes some environment variables:
+
+* `MIRI_SYSROOT` (recognized by `miri`, `cargo miri` and the test suite)
+  indicates the sysroot to use.
+* `MIRI_TARGET` (recognized by the test suite) indicates which target
+  architecture to test against.  `miri` and `cargo miri` accept the `--target`
+  flag for the same purpose.
+
 ## Contributing and getting help
 
 Check out the issues on this GitHub repository for some ideas. There's lots that

tests/compiletest.rs

@@ -34,10 +34,11 @@ fn mk_config(mode: &str) -> compiletest::common::ConfigWithTemp {
         config.compile_lib_path = rustc_lib_path();
     }
     config.filter = env::args().nth(1);
+    config.host = get_host();
     config
 }
 
-fn compile_fail(sysroot: &Path, path: &str, target: &str, host: &str, opt: bool) {
+fn compile_fail(path: &str, target: &str, opt: bool) {
     let opt_str = if opt { " with optimizations" } else { "" };
     eprintln!("{}", format!(
         "## Running compile-fail tests in {} against miri for target {}{}",
@@ -47,7 +48,6 @@ fn compile_fail(sysroot: &Path, path: &str, target: &str, host: &str, opt: bool)
     ).green().bold());
 
     let mut flags = Vec::new();
-    flags.push(format!("--sysroot {}", sysroot.display()));
     flags.push("-Dwarnings -Dunused".to_owned()); // overwrite the -Aunused in compiletest-rs
     flags.push("--edition 2018".to_owned());
     if opt {
@@ -60,12 +60,11 @@ fn compile_fail(sysroot: &Path, path: &str, target: &str, host: &str, opt: bool)
     let mut config = mk_config("compile-fail");
     config.src_base = PathBuf::from(path);
     config.target = target.to_owned();
-    config.host = host.to_owned();
     config.target_rustcflags = Some(flags.join(" "));
     compiletest::run_tests(&config);
 }
 
-fn miri_pass(sysroot: &Path, path: &str, target: &str, host: &str, opt: bool) {
+fn miri_pass(path: &str, target: &str, opt: bool) {
     let opt_str = if opt { " with optimizations" } else { "" };
     eprintln!("{}", format!(
         "## Running run-pass tests in {} against miri for target {}{}",
@@ -75,7 +74,6 @@ fn miri_pass(sysroot: &Path, path: &str, target: &str, host: &str, opt: bool) {
     ).green().bold());
 
     let mut flags = Vec::new();
-    flags.push(format!("--sysroot {}", sysroot.display()));
     flags.push("-Dwarnings -Dunused".to_owned()); // overwrite the -Aunused in compiletest-rs
     flags.push("--edition 2018".to_owned());
     if opt {
@@ -87,57 +85,24 @@ fn miri_pass(sysroot: &Path, path: &str, target: &str, host: &str, opt: bool) {
     let mut config = mk_config("ui");
     config.src_base = PathBuf::from(path);
     config.target = target.to_owned();
-    config.host = host.to_owned();
     config.target_rustcflags = Some(flags.join(" "));
     compiletest::run_tests(&config);
 }
 
-fn is_target_dir<P: Into<PathBuf>>(path: P) -> bool {
-    let mut path = path.into();
-    path.push("lib");
-    path.metadata().map(|m| m.is_dir()).unwrap_or(false)
-}
-
-fn target_has_std<P: Into<PathBuf>>(path: P) -> bool {
-    let mut path = path.into();
-    path.push("lib");
-    std::fs::read_dir(path)
-        .expect("invalid target")
-        .map(|entry| entry.unwrap())
-        .filter(|entry| entry.file_type().unwrap().is_file())
-        .filter_map(|entry| entry.file_name().into_string().ok())
-        .any(|file_name| file_name == "libstd.rlib")
-}
-
-
-fn for_all_targets<F: FnMut(String)>(sysroot: &Path, f: F) {
-    let target_dir = sysroot.join("lib").join("rustlib");
-    let mut targets = std::fs::read_dir(target_dir)
-        .expect("invalid sysroot")
-        .map(|entry| entry.unwrap())
-        .filter(|entry| is_target_dir(entry.path()))
-        .filter(|entry| target_has_std(entry.path()))
-        .map(|entry| entry.file_name().into_string().unwrap())
-        .peekable();
-
-    if targets.peek().is_none() {
-        panic!("No valid targets found");
+/// Make sure the MIRI_SYSROOT env var is set
+fn set_sysroot() {
+    if std::env::var("MIRI_SYSROOT").is_ok() {
+        // Nothing to do
+        return;
     }
-
-    targets.for_each(f);
-}
-
-fn get_sysroot() -> PathBuf {
-    let sysroot = std::env::var("MIRI_SYSROOT").unwrap_or_else(|_| {
-        let sysroot = std::process::Command::new("rustc")
-            .arg("--print")
-            .arg("sysroot")
-            .output()
-            .expect("rustc not found")
-            .stdout;
-        String::from_utf8(sysroot).expect("sysroot is not utf8")
-    });
-    PathBuf::from(sysroot.trim())
+    let sysroot = std::process::Command::new("rustc")
+        .arg("--print")
+        .arg("sysroot")
+        .output()
+        .expect("rustc not found")
+        .stdout;
+    let sysroot = String::from_utf8(sysroot).expect("sysroot is not utf8");
+    std::env::set_var("MIRI_SYSROOT", sysroot.trim());
 }
 
 fn get_host() -> String {
@@ -153,28 +118,20 @@ fn get_host() -> String {
     version_meta.host
 }
 
-fn run_pass_miri(opt: bool) {
-    let sysroot = get_sysroot();
-    let host = get_host();
+fn get_target() -> String {
+    std::env::var("MIRI_TARGET").unwrap_or_else(|_| get_host())
+}
 
-    for_all_targets(&sysroot, |target| {
-        miri_pass(&sysroot, "tests/run-pass", &target, &host, opt);
-    });
+fn run_pass_miri(opt: bool) {
+    miri_pass("tests/run-pass", &get_target(), opt);
 }
 
 fn compile_fail_miri(opt: bool) {
-    let sysroot = get_sysroot();
-    let host = get_host();
-
-    for_all_targets(&sysroot, |target| {
-        compile_fail(&sysroot, "tests/compile-fail", &target, &host, opt);
-    });
+    compile_fail("tests/compile-fail", &get_target(), opt);
 }
 
 fn test_runner(_tests: &[&()]) {
-    // We put everything into a single test to avoid the parallelism `cargo test`
-    // introduces.  We still get parallelism within our tests because `compiletest`
-    // uses `libtest` which runs jobs in parallel.
+    set_sysroot();
 
     run_pass_miri(false);
     run_pass_miri(true);