Auto merge of #1726 - hyd-dev:stub-d, r=RalfJung

cargo-miri: create stub .d files

Thanks `@RalfJung` for the discovery: #1724 (comment) ❤️
Fixes #1724.

Author: bors

cargo-miri/bin.rs

@@ -609,6 +609,15 @@ fn phase_cargo_rustc(mut args: env::Args) {
     let print = get_arg_flag_value("--print").is_some(); // whether this is cargo passing `--print` to get some infos
 
     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 {
+            eprintln!("[cargo-miri rustc] writing stub dep-info to `{}`", dep_info_name.display());
+        }
+        File::create(dep_info_name).expect("failed to create fake .d file");
+
         let filename = out_filename("", "");
         if verbose {
             eprintln!("[cargo-miri rustc] writing run info to `{}`", filename.display());

test-cargo-miri/run-test.py

@@ -50,12 +50,15 @@ def test(name, cmd, stdout_ref, stderr_ref, stdin=b'', env={}):
     print("--- END stderr ---")
     fail("exit code was {}".format(p.returncode))
 
-def test_no_rebuild(name, cmd):
+def test_no_rebuild(name, cmd, env={}):
     print("Testing {}...".format(name))
+    p_env = os.environ.copy()
+    p_env.update(env)
     p = subprocess.Popen(
         cmd,
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE,
+        env=p_env,
     )
     (stdout, stderr) = p.communicate()
     stdout = stdout.decode("UTF-8")
@@ -79,6 +82,12 @@ def test_cargo_miri_run():
             'MIRITESTVAR': "wrongval", # make sure the build.rs value takes precedence
         },
     )
+    # Special test: run it again *without* `-q` to make sure nothing is being rebuilt (Miri issue #1722)
+    test_no_rebuild("`cargo miri run` (no rebuild)",
+        cargo_miri("run", quiet=False) + ["--", ""],
+        env={'MIRITESTVAR': "wrongval"}, # changing the env var causes a rebuild (re-runs build.rs),
+                                         # so keep it set
+    )
     test("`cargo miri run` (with arguments and target)",
         cargo_miri("run") + ["--bin", "cargo-miri-test", "--", "hello world", '"hello world"'],
         "run.args.stdout.ref", "run.args.stderr.ref",
@@ -88,12 +97,6 @@ def test_cargo_miri_run():
         "run.subcrate.stdout.ref", "run.subcrate.stderr.ref",
         env={'MIRIFLAGS': "-Zmiri-disable-isolation"},
     )
-    # Special test: run it again *without* `-q` to make sure nothing is being rebuilt (Miri issue #1722)
-    # FIXME: move this test up to right after the first `test`
-    # (currently that fails, only the 3rd and later runs are really clean... see Miri issue #1722)
-    test_no_rebuild("`cargo miri run` (no rebuild)",
-        cargo_miri("run", quiet=False) + ["--", ""],
-    )
 
 def test_cargo_miri_test():
     # rustdoc is not run on foreign targets