bpo-31908: Fix output of cover files for trace module command-line tool. (GH-4205)

Previously emitted cover files only when --missing option was used.

Lib/test/test_trace.py

@@ -2,6 +2,7 @@ import os
 import sys
 from test.support import TESTFN, rmtree, unlink, captured_stdout
 from test.support.script_helper import assert_python_ok, assert_python_failure
+import textwrap
 import unittest
 
 import trace
@@ -365,6 +366,46 @@ class Test_Ignore(unittest.TestCase):
         # Matched before.
         self.assertTrue(ignore.names(jn('bar', 'baz.py'), 'baz'))
 
+# Created for Issue 31908 -- CLI utility not writing cover files
+class TestCoverageCommandLineOutput(unittest.TestCase):
+
+    codefile = 'tmp.py'
+    coverfile = 'tmp.cover'
+
+    def setUp(self):
+        with open(self.codefile, 'w') as f:
+            f.write(textwrap.dedent('''\
+                x = 42
+                if []:
+                    print('unreachable')
+            '''))
+
+    def tearDown(self):
+        unlink(self.codefile)
+        unlink(self.coverfile)
+
+    def test_cover_files_written_no_highlight(self):
+        argv = '-m trace --count'.split() + [self.codefile]
+        status, stdout, stderr = assert_python_ok(*argv)
+        self.assertTrue(os.path.exists(self.coverfile))
+        with open(self.coverfile) as f:
+            self.assertEqual(f.read(),
+                "    1: x = 42\n"
+                "    1: if []:\n"
+                "           print('unreachable')\n"
+            )
+
+    def test_cover_files_written_with_highlight(self):
+        argv = '-m trace --count --missing'.split() + [self.codefile]
+        status, stdout, stderr = assert_python_ok(*argv)
+        self.assertTrue(os.path.exists(self.coverfile))
+        with open(self.coverfile) as f:
+            self.assertEqual(f.read(), textwrap.dedent('''\
+                    1: x = 42
+                    1: if []:
+                >>>>>>     print('unreachable')
+            '''))
+
 class TestCommandLine(unittest.TestCase):
 
     def test_failures(self):

Lib/trace.py

@@ -73,9 +73,6 @@ def _unsettrace():
 
 PRAGMA_NOCOVER = "#pragma NO COVER"
 
-# Simple rx to find lines with no code.
-rx_blank = re.compile(r'^\s*(#.*)?$')
-
 class _Ignore:
     def __init__(self, modules=None, dirs=None):
         self._mods = set() if not modules else set(modules)
@@ -278,7 +275,6 @@ class CoverageResults:
                 lnotab = _find_executable_linenos(filename)
             else:
                 lnotab = {}
-            if lnotab:
             source = linecache.getlines(filename)
             coverpath = os.path.join(dir, modulename + ".cover")
             with open(filename, 'rb') as fp:
@@ -306,6 +302,7 @@ class CoverageResults:
 
     def write_results_file(self, path, lines, lnotab, lines_hit, encoding=None):
         """Return a coverage results file in path."""
+        # ``lnotab`` is a dict of executable lines, or a line number "table"
 
         try:
             outfile = open(path, "w", encoding=encoding)
@@ -324,13 +321,9 @@ class CoverageResults:
                     outfile.write("%5d: " % lines_hit[lineno])
                     n_hits += 1
                     n_lines += 1
-                elif rx_blank.match(line):
-                    outfile.write("       ")
-                else:
-                    # lines preceded by no marks weren't hit
-                    # Highlight them if so indicated, unless the line contains
+                elif lineno in lnotab and not PRAGMA_NOCOVER in line:
+                    # Highlight never-executed lines, unless the line contains
                     # #pragma: NO COVER
-                    if lineno in lnotab and not PRAGMA_NOCOVER in line:
                     outfile.write(">>>>>> ")
                     n_lines += 1
                 else:

Misc/NEWS.d/next/Library/2017-10-31.bpo-31908.g4xh8x.rst

@@ -0,0 +1,3 @@
+Fix output of cover files for ``trace`` module command-line tool.
+Previously emitted cover files only when ``--missing`` option was used.
+Patch by Michael Selik.