bitbake: build: Make python output print to stdout when running with -v (verbose)

When tasks are run with -v (verbose) on the bitbake commandline, shell
tasks print their stdout, python tasks do not.

This change redirects the python task's print output to an in memory
buffer. After the task is executed the output is printed to stdout via
the logger. This makes the python task behavior match the shell task
behavior when running with -v. The contents of the task's log files
remain unchanged after this change.

This approach should keep the correct order in most cases, however, if
the python task accesses the logger directly, that content will appear
before other output. On the other hand, this change should negate the
need for python tasks to access the logger directly.

Special care is taken to save/restore the existing stdout and stderr
and preventing sending output directly to the logger when there are
"recursive" calls, for instance when a python function calls a shell
function, avoiding printing things potentially out of order and/or
multiple times.

The logging-test.bb in meta-selftest can be used to review this
change. This has been tested with the full bblogging oeqa tests.

[Yocto #14544]

(Bitbake rev: 81a58647b2f4fc0a2589b2978fc9d81b2bfe6aec)

Signed-off-by: Mark Asselstine <mark.asselstine@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/build.py

@@ -25,6 +25,7 @@ import bb
 import bb.msg
 import bb.process
 import bb.progress
+from io import StringIO
 from bb import data, event, utils
 
 bblogger = logging.getLogger('BitBake')
@@ -177,7 +178,9 @@ class StdoutNoopContextManager:
 
     @property
     def name(self):
-        return sys.stdout.name
+        if "name" in dir(sys.stdout):
+            return sys.stdout.name
+        return "<mem>"
 
 
 def exec_func(func, d, dirs = None):
@@ -296,9 +299,21 @@ def exec_func_python(func, d, runfile, cwd=None):
         lineno = int(d.getVarFlag(func, "lineno", False))
         bb.methodpool.insert_method(func, text, fn, lineno - 1)
 
+        if verboseStdoutLogging:
+            sys.stdout.flush()
+            sys.stderr.flush()
+            currout = sys.stdout
+            currerr = sys.stderr
+            sys.stderr = sys.stdout = execio = StringIO()
         comp = utils.better_compile(code, func, "exec_func_python() autogenerated")
         utils.better_exec(comp, {"d": d}, code, "exec_func_python() autogenerated")
     finally:
+        if verboseStdoutLogging:
+            execio.flush()
+            logger.plain("%s" % execio.getvalue())
+            sys.stdout = currout
+            sys.stderr = currerr
+            execio.close()
         # We want any stdout/stderr to be printed before any other log messages to make debugging
         # more accurate. In some cases we seem to lose stdout/stderr entirely in logging tests without this.
         sys.stdout.flush()
@@ -441,7 +456,11 @@ exit $ret
         if fakerootcmd:
             cmd = [fakerootcmd, runfile]
 
-    if verboseStdoutLogging:
+    # We only want to output to logger via LogTee if stdout is sys.__stdout__ (which will either
+    # be real stdout or subprocess PIPE or similar). In other cases we are being run "recursively",
+    # ie. inside another function, in which case stdout is already being captured so we don't
+    # want to Tee here as output would be printed twice, and out of order.
+    if verboseStdoutLogging and sys.stdout == sys.__stdout__:
         logfile = LogTee(logger, StdoutNoopContextManager())
     else:
         logfile = StdoutNoopContextManager()