gpython: Implement -v

Tracing import statements might be handy while debugging things
related to initialization. Implementation is simple reexecution of
underlying python with that same -v like we already do for -O, -E and -X.

/reviewed-by @jerome
/reviewed-on nexedi/pygolang!30

gpython/__init__.py

@@ -41,7 +41,7 @@ $GPYTHON_RUNTIME=threads.
 from __future__ import print_function, absolute_import
 
 
-_pyopt = "c:Eim:OVW:X:"
+_pyopt = "c:Eim:OvVW:X:"
 _pyopt_long = ('version',)
 
 # pymain mimics `python ...`
@@ -115,6 +115,7 @@ def pymain(argv, init=None):
         if opt in (
                 '-E',   # ignore $PYTHON*
                 '-O',   # optimize
+                '-v',   # trace import statements
                 '-X',   # set implementation-specific option
             ):
 

gpython/gpython_test.py

@@ -347,6 +347,29 @@ def test_pymain_X():
     check_gpy_vs_py(['-X', 'faulthandler', 'testprog/print_faulthandler.py'], cwd=here)
 
 
+# pymain -v
+@gpython_only
+def test_pymain_v():
+    def nimport(argv, **kw):
+        argv = argv + ['testdata/hello.py']
+        kw.setdefault('cwd', here)
+        ret, out, err = _pyrun(argv, stdout=PIPE, stderr=PIPE, **kw)
+        assert ret == 0,    (out, err)
+        n = 0
+        for _ in u(err).splitlines():
+            if _.startswith("import "):
+                n += 1
+        return n
+
+    # without -v there must be no "import ..." messages
+    assert nimport([])                                              == 0
+    assert nimport([], pyexe=sys._gpy_underlying_executable)        == 0
+
+    # with    -v there must be many "import ..." messages
+    assert nimport(['-v'])                                          >  10
+    assert nimport(['-v'], pyexe=sys._gpy_underlying_executable)    >  10
+
+
 # pymain -V/--version
 # gpython_only because output differs from !gpython.
 @gpython_only