mtest: read test stdout/stderr via asyncio pipes

Instead of creating temporary files, get the StreamReaders from
_run_subprocess's returned object. Through asyncio magic, their
contents will be read as it becomes ready and then returned when
the StreamReader.read future is awaited.

Because of this change, the stdout and stderr can be easily
preserved when TestSubprocess returns an additional_error.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

mesonbuild/mtest.py

@@ -32,7 +32,6 @@ import re
 import signal
 import subprocess
 import sys
-import tempfile
 import textwrap
 import time
 import typing as T
@@ -929,6 +928,14 @@ class TestSubprocess:
         self._process = p
         self.postwait_fn = postwait_fn   # type: T.Callable[[], None]
 
+    @property
+    def stdout(self) -> T.Optional[asyncio.StreamReader]:
+        return self._process.stdout
+
+    @property
+    def stderr(self) -> T.Optional[asyncio.StreamReader]:
+        return self._process.stderr
+
     async def _kill(self) -> T.Optional[str]:
         # Python does not provide multiplatform support for
         # killing a process and all its children so we need
@@ -1033,7 +1040,7 @@ class SingleTestRunner:
         return self.runobj
 
     async def _run_subprocess(self, args: T.List[str], *,
-                              stdout: T.IO, stderr: T.IO,
+                              stdout: int, stderr: int,
                               env: T.Dict[str, str], cwd: T.Optional[str]) -> TestSubprocess:
         # Let gdb handle ^C instead of us
         if self.options.gdb:
@@ -1088,11 +1095,12 @@ class SingleTestRunner:
 
         stdout = None
         stderr = None
-        if not self.options.verbose:
-            stdout = tempfile.TemporaryFile("wb+")
-            stderr = tempfile.TemporaryFile("wb+") if self.options.split else stdout
-        if self.test.protocol is TestProtocol.TAP and stderr is stdout:
-            stdout = tempfile.TemporaryFile("wb+")
+        if self.test.protocol is TestProtocol.TAP:
+            stdout = asyncio.subprocess.PIPE
+            stderr = None if self.options.verbose else asyncio.subprocess.PIPE
+        elif not self.options.verbose:
+            stdout = asyncio.subprocess.PIPE
+            stderr = asyncio.subprocess.PIPE if self.options.split else asyncio.subprocess.STDOUT
 
         extra_cmd = []  # type: T.List[str]
         if self.test.protocol is TestProtocol.GTEST:
@@ -1114,24 +1122,24 @@ class SingleTestRunner:
                                        env=self.env,
                                        cwd=self.test.workdir)
 
+        stdo = stde = ''
+        stdo_task = stde_task = None
+        if stdout is not None:
+            stdo_task = p.stdout.read(-1)
+        if stderr is not None and stderr != asyncio.subprocess.STDOUT:
+            stde_task = p.stderr.read(-1)
+
         returncode, result, additional_error = await p.wait(timeout)
         if result is TestResult.TIMEOUT and self.options.verbose:
             print('{} time out (After {} seconds)'.format(self.test.name, timeout))
 
-        if additional_error is None:
-            if stdout is None:
-                stdo = ''
-            else:
-                stdout.seek(0)
-                stdo = decode(stdout.read())
-            if stderr is None or stderr is stdout:
-                stde = ''
-            else:
-                stderr.seek(0)
-                stde = decode(stderr.read())
-        else:
-            stdo = ""
-            stde = additional_error
+        if stdo_task is not None:
+            stdo = decode(await stdo_task)
+        if stde_task is not None:
+            stde = decode(await stde_task)
+
+        if additional_error is not None:
+            stde += '\n' + additional_error
 
         # Print lines along the way if requested
         def lines() -> T.Iterator[str]: