[duplicate-code] Fix crash when analysing empty function with docstring

Closes #4648

ChangeLog

@@ -17,6 +17,10 @@ Release date: TBA
 ..
   Put bug fixes that should not wait for a new minor version here
 
+* Fix a crash that happened when analysing empty function with docstring
+  using in the ``similarity`` checker.
+
+  Closes #4648
 
 
 What's New in Pylint 2.9.2?

pylint/checkers/similar.py

@@ -218,7 +218,13 @@ def stripped_lines(
             if isinstance(n, (astroid.FunctionDef, astroid.AsyncFunctionDef))
         ]
         signature_lines = set(
-            chain(*(range(func.fromlineno, func.body[0].lineno) for func in functions))
+            chain(
+                *(
+                    range(func.fromlineno, func.body[0].lineno)
+                    for func in functions
+                    if func.body
+                )
+            )
         )
 
     strippedlines = []

tests/checkers/unittest_similar.py

@@ -164,8 +164,8 @@ def test_ignore_signatures_fail():
     assert (
         output.getvalue().strip()
         == (
-            """
-7 similar lines in 2 files
+            '''
+10 similar lines in 2 files
 ==%s:1
 ==%s:8
        arg1: int = 3,
@@ -175,8 +175,11 @@ def test_ignore_signatures_fail():
        arg5: int = 5
    ) -> Ret1:
        pass
-TOTAL lines=23 duplicates=7 percent=30.43
-"""
+   
+   def example():
+       """Valid function definition with docstring only."""
+TOTAL lines=29 duplicates=10 percent=34.48
+'''
             % (SIMILAR5, SIMILAR6)
         ).strip()
     )
@@ -190,7 +193,7 @@ def test_ignore_signatures_pass():
     assert (
         output.getvalue().strip()
         == """
-TOTAL lines=23 duplicates=0 percent=0.00
+TOTAL lines=29 duplicates=0 percent=0.00
 """.strip()
     )
 

tests/input/similar5

@@ -6,3 +6,6 @@ def func1(
     arg5: int = 5
 ) -> Ret1:
     pass
+
+def example():
+    """Valid function definition with docstring only."""

tests/input/similar6

@@ -13,3 +13,6 @@ async def func2(
     arg5: int = 5
 ) -> Ret1:
     pass
+
+def example():
+    """Valid function definition with docstring only."""