Fix source reindenting by using `textwrap.dedent` directly.

changelog/4066.bugfix.rst

@@ -0,0 +1 @@
+Fix source reindenting by using ``textwrap.dedent`` directly.

src/_pytest/_code/source.py

@@ -7,6 +7,7 @@ import linecache
 import sys
 import six
 import inspect
+import textwrap
 import tokenize
 import py
 
@@ -23,7 +24,6 @@ class Source(object):
     def __init__(self, *parts, **kwargs):
         self.lines = lines = []
         de = kwargs.get("deindent", True)
-        rstrip = kwargs.get("rstrip", True)
         for part in parts:
             if not part:
                 partlines = []
@@ -33,11 +33,6 @@ class Source(object):
                 partlines = [x.rstrip("\n") for x in part]
             elif isinstance(part, six.string_types):
                 partlines = part.split("\n")
-                if rstrip:
-                    while partlines:
-                        if partlines[-1].strip():
-                            break
-                        partlines.pop()
             else:
                 partlines = getsource(part, deindent=de).lines
             if de:
@@ -269,46 +264,7 @@ def getsource(obj, **kwargs):
 
 
 def deindent(lines, offset=None):
-    if offset is None:
-        for line in lines:
-            line = line.expandtabs()
-            s = line.lstrip()
-            if s:
-                offset = len(line) - len(s)
-                break
-        else:
-            offset = 0
-    if offset == 0:
-        return list(lines)
-    newlines = []
-
-    def readline_generator(lines):
-        for line in lines:
-            yield line + "\n"
-
-    it = readline_generator(lines)
-
-    try:
-        for _, _, (sline, _), (eline, _), _ in tokenize.generate_tokens(
-            lambda: next(it)
-        ):
-            if sline > len(lines):
-                break  # End of input reached
-            if sline > len(newlines):
-                line = lines[sline - 1].expandtabs()
-                if line.lstrip() and line[:offset].isspace():
-                    line = line[offset:]  # Deindent
-                newlines.append(line)
-
-            for i in range(sline, eline):
-                # Don't deindent continuing lines of
-                # multiline tokens (i.e. multiline strings)
-                newlines.append(lines[i])
-    except (IndentationError, tokenize.TokenError):
-        pass
-    # Add any lines we didn't see. E.g. if an exception was raised.
-    newlines.extend(lines[len(newlines) :])
-    return newlines
+    return textwrap.dedent("\n".join(lines)).splitlines()
 
 
 def get_statement_startend2(lineno, node):

testing/code/test_source.py

@@ -27,16 +27,7 @@ def test_source_str_function():
     x = Source(
         """
         3
-    """,
-        rstrip=False,
-    )
-    assert str(x) == "\n3\n    "
-
-    x = Source(
         """
-        3
-    """,
-        rstrip=True,
     )
     assert str(x) == "\n3"
 
@@ -400,10 +391,13 @@ def test_getfuncsource_with_multine_string():
     pass
 """
 
-    assert (
-        str(_pytest._code.Source(f)).strip()
-        == 'def f():\n    c = """while True:\n    pass\n"""'
-    )
+    expected = '''\
+    def f():
+        c = """while True:
+    pass
+"""
+'''
+    assert str(_pytest._code.Source(f)) == expected.rstrip()
 
 
 def test_deindent():
@@ -417,7 +411,7 @@ def test_deindent():
 """
 
     lines = deindent(inspect.getsource(f).splitlines())
-    assert lines == ["def f():", '    c = """while True:', "    pass", '"""']
+    assert lines == ["    def f():", '        c = """while True:', "    pass", '"""']
 
     source = """
         def f():
@@ -425,7 +419,7 @@ def test_deindent():
                 pass
     """
     lines = deindent(source.splitlines())
-    assert lines == ["", "def f():", "    def g():", "        pass", "    "]
+    assert lines == ["", "def f():", "    def g():", "        pass"]
 
 
 def test_source_of_class_at_eof_without_newline(tmpdir):