rewrite cargo-miri test in Python

.travis.yml

@@ -36,35 +36,18 @@ script:
 - |
   # Test and install plain miri
   cargo build --release --all-features &&
-  #cargo test --release --all-features &&
+  cargo test --release --all-features &&
   cargo install --all-features --force --path .
 - |
   # get ourselves a MIR-full libstd
   xargo/build.sh &&
   export MIRI_SYSROOT=~/.xargo/HOST
-#- |
-#  # run all tests with full mir
-#  cargo test --release --all-features
+- |
+  # run all tests with full mir
+  cargo test --release --all-features
 - |
   # Test cargo integration
-  cd cargo-miri-test &&
-  # Test `cargo miri`
-    # We ignore the exit code because we want to see the output even on failure, and
-    # I found no way to preserve the exit code so that we can test for it later.
-    # Variables set in this subshell in the parenthesis are not available
-    # on the outside.
-    # We assume that if this fails, it'll also print something about the failure on
-    # stdout/stderr and we'll catch that.
-    # FIXME: Disabling validation, still investigating whether there is UB here
-    (cargo miri -q >stdout.real 2>stderr.real -- -Zmiri-disable-validation || true) &&
-    # Print file names and contents (`cat` would just print contents)
-    tail -n +0 stdout.real stderr.real &&
-    # Verify output
-    diff -u stdout.ref stdout.real &&
-    diff -u stderr.ref stderr.real &&
-  # test `cargo miri test`
-    cargo miri test &&
-  cd ..
+  (cd cargo-miri-test && ./run-test.py)
 
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cargo-miri-test/run-test.py

@@ -0,0 +1,43 @@
+#!/usr/bin/python3
+'''
+Test whether cargo-miri works properly.
+Assumes the `MIRI_SYSROOT` env var to be set appropriately,
+and the working directory to contain the cargo-miri-test project.
+'''
+
+import sys, subprocess
+
+def test_cargo_miri():
+    print("==> Testing `cargo miri` <==")
+    ## Call `cargo miri`, capture all output
+    # FIXME: Disabling validation, still investigating whether there is UB here
+    p = subprocess.Popen(
+        ["cargo", "miri", "-q", "--", "-Zmiri-disable-validation"],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE
+    )
+    (stdout, stderr) = p.communicate()
+    stdout = stdout.decode("UTF-8")
+    stderr = stderr.decode("UTF-8")
+    # Show output
+    print("=> captured stdout <=")
+    print(stdout, end="")
+    print("=> captured stderr <=")
+    print(stderr, end="")
+    # Test for failures
+    if p.returncode != 0:
+        sys.exit(1)
+    if stdout != open('stdout.ref').read():
+        print("stdout does not match reference")
+        sys.exit(1)
+    if stderr != open('stderr.ref').read():
+        print("stderr does not match reference")
+        sys.exit(1)
+
+def test_cargo_miri_test():
+    print("==> Testing `cargo miri test` <==")
+    subprocess.check_call(["cargo", "miri", "test"])
+
+test_cargo_miri()
+test_cargo_miri_test()
+sys.exit(0)