mtest: tweak the gathering of stdo_task/stde_task results

After the next patch, we will need to complete parse_task before
stdo_task (because parse_task will not set the "stdo" variable
anymore but it will still collect stdout just like now).  Do
the change now to isolate the more complicated changes.

1 files changed, 14 insertions, 9 deletions

diff --git a/mesonbuild/mtest.py b/mesonbuild/mtest.py
index f112177..300eb11 100644
--- a/mesonbuild/mtest.py
+++ b/mesonbuild/mtest.py
@@ -147,6 +147,13 @@ def print_safe(s: str) -> None:
         s = s.encode('ascii', errors='backslashreplace').decode('ascii')
         print(s)
 
+def join_lines(a: str, b: str) -> str:
+    if not a:
+        return b
+    if not b:
+        return a
+    return a + '\n' + b
+
 def returncode_to_status(retcode: int) -> str:
     # Note: We can't use `os.WIFSIGNALED(result.returncode)` and the related
     # functions here because the status returned by subprocess is munged. It
@@ -1266,20 +1273,18 @@ class SingleTestRunner:
 
         returncode, result, additional_error = await p.wait(self.runobj.timeout)
 
-        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
-
         if parse_task is not None:
             res, error = await parse_task
             if error:
-                stde += '\n' + error
+                additional_error = join_lines(additional_error, error)
             result = result or res
 
+        if stdo_task is not None:
+            stdo = decode(await stdo_task)
+        if stde_task is not None:
+            stde = decode(await stde_task)
+
+        stde = join_lines(stde, additional_error)
         self.runobj.complete(returncode, result, stdo, stde)