fix syntax error reporting from stdin (#357)

pyflakes/api.py

@@ -55,14 +55,7 @@ def check(codeString, filename, reporter=None):
                             text = None
             offset -= 1
 
-        # If there's an encoding problem with the file, the text is None.
-        if text is None:
-            # Avoid using msg, since for the only known case, it contains a
-            # bogus message that claims the encoding the file declared was
-            # unknown.
-            reporter.unexpectedError(filename, 'problem decoding source')
-        else:
-            reporter.syntaxError(filename, msg, lineno, offset, text)
+        reporter.syntaxError(filename, msg, lineno, offset, text)
         return 1
     except Exception:
         reporter.unexpectedError(filename, 'problem decoding source')

pyflakes/reporter.py

@@ -51,19 +51,30 @@ def syntaxError(self, filename, msg, lineno, offset, text):
         @param text: The source code containing the syntax error.
         @ptype text: C{unicode}
         """
-        line = text.splitlines()[-1]
+        if text is None:
+            line = None
+        else:
+            line = text.splitlines()[-1]
+
+        # lineno might be 0 if the error came from stdin
+        lineno = max(lineno, 1)
+
         if offset is not None:
-            if sys.version_info < (3, 8):
+            if sys.version_info < (3, 8) and text is not None:
                 offset = offset - (len(text) - len(line)) + 1
+            # some versions of python emit an offset of -1 for certain encoding errors
+            offset = max(offset, 1)
             self._stderr.write('%s:%d:%d: %s\n' %
                                (filename, lineno, offset, msg))
         else:
             self._stderr.write('%s:%d: %s\n' % (filename, lineno, msg))
-        self._stderr.write(line)
-        self._stderr.write('\n')
-        if offset is not None:
-            self._stderr.write(re.sub(r'\S', ' ', line[:offset - 1]) +
-                               "^\n")
+
+        if line is not None:
+            self._stderr.write(line)
+            self._stderr.write('\n')
+            if offset is not None:
+                self._stderr.write(re.sub(r'\S', ' ', line[:offset - 1]) +
+                                   "^\n")
 
     def flake(self, message):
         """

pyflakes/test/test_api.py

@@ -15,6 +15,7 @@
 from pyflakes.reporter import Reporter
 from pyflakes.api import (
     main,
+    check,
     checkPath,
     checkRecursive,
     iterSourceCode,
@@ -255,6 +256,17 @@ def test_syntaxErrorNoOffset(self):
              "bad line of source\n"),
             err.getvalue())
 
+    def test_syntaxErrorNoText(self):
+        """
+        C{syntaxError} doesn't include text or nonsensical offsets if C{text} is C{None}.
+
+        This typically happens when reporting syntax errors from stdin.
+        """
+        err = io.StringIO()
+        reporter = Reporter(None, err)
+        reporter.syntaxError('<stdin>', 'a problem', 0, 0, None)
+        self.assertEqual(("<stdin>:1:1: a problem\n"), err.getvalue())
+
     def test_multiLineSyntaxError(self):
         """
         If there's a multi-line syntax error, then we only report the last
@@ -606,7 +618,8 @@ def test_misencodedFileUTF8(self):
 """ % SNOWMAN).encode('utf-8')
         with self.makeTempFile(source) as sourcePath:
             self.assertHasErrors(
-                sourcePath, [f"{sourcePath}: problem decoding source\n"])
+                sourcePath,
+                [f"{sourcePath}:1:1: 'ascii' codec can't decode byte 0xe2 in position 21: ordinal not in range(128)\n"])  # noqa: E501
 
     def test_misencodedFileUTF16(self):
         """
@@ -648,6 +661,43 @@ def test_checkRecursive(self):
         finally:
             shutil.rmtree(tempdir)
 
+    def test_stdinReportsErrors(self):
+        """
+        L{check} reports syntax errors from stdin
+        """
+        source = "max(1 for i in range(10), key=lambda x: x+1)\n"
+        err = io.StringIO()
+        count = withStderrTo(err, check, source, "<stdin>")
+        self.assertEqual(count, 1)
+        errlines = err.getvalue().split("\n")[:-1]
+
+        if PYPY:
+            expected_error = [
+                "<stdin>:1:3: Generator expression must be parenthesized if not sole argument",  # noqa: E501
+                "max(1 for i in range(10), key=lambda x: x+1)",
+                "  ^",
+            ]
+        elif sys.version_info >= (3, 9):
+            expected_error = [
+                "<stdin>:1:5: Generator expression must be parenthesized",
+                "max(1 for i in range(10), key=lambda x: x+1)",
+                "    ^",
+            ]
+        elif sys.version_info >= (3, 8):
+            expected_error = [
+                "<stdin>:1:5: Generator expression must be parenthesized",
+            ]
+        elif sys.version_info >= (3, 7):
+            expected_error = [
+                "<stdin>:1:4: Generator expression must be parenthesized",
+            ]
+        elif sys.version_info >= (3, 6):
+            expected_error = [
+                "<stdin>:1:4: Generator expression must be parenthesized if not sole argument",  # noqa: E501
+            ]
+
+        self.assertEqual(errlines, expected_error)
+
 
 class IntegrationTests(TestCase):
     """