inspect: Fix getsource() to support decorated functions.

Issue #1764286. Patch by Claudiu Popa.

Lib/inspect.py

@@ -817,6 +817,7 @@ def getsourcelines(object):
     corresponding to the object and the line number indicates where in the
     original source file the first line of code was found.  An OSError is
     raised if the source code cannot be retrieved."""
+    object = unwrap(object)
     lines, lnum = findsource(object)
 
     if ismodule(object): return lines, 0

Lib/test/inspect_fodder2.py

@@ -109,3 +109,16 @@ def annotated(arg1: list):
 #line 109
 def keyword_only_arg(*, arg):
     pass
+
+from functools import wraps
+
+def decorator(func):
+    @wraps(func)
+    def fake():
+        return 42
+    return fake
+
+#line 121
+@decorator
+def real():
+    return 20

Lib/test/test_inspect.py

@@ -377,6 +377,9 @@ class TestDecorators(GetSourceBase):
     def test_replacing_decorator(self):
         self.assertSourceEqual(mod2.gone, 9, 10)
 
+    def test_getsource_unwrap(self):
+        self.assertSourceEqual(mod2.real, 122, 124)
+
 class TestOneliners(GetSourceBase):
     fodderModule = mod2
     def test_oneline_lambda(self):

Misc/NEWS

@@ -10,6 +10,9 @@ Release date: TBA
 Core and Builtins
 -----------------
 
+- Issue #1764286: Fix inspect.getsource() to support decorated functions.
+  Patch by Claudiu Popa.
+
 - Issue #18554: os.__all__ includes posix functions.
 
 - Issue #21391: Use os.path.abspath in the shutil module.