Added a new refactoring warning, 'simplifiable-if-statement'

This is used when an if statement could be reduced to a boolean evaluation
of its test, as seen in this example:

   if some_cond:
      return True
   else:
      return False

   could be reduced to `return bool(some_cond)`

Closes issue #698.

2 files changed, 124 insertions, 0 deletions

diff --git a/pylint/test/functional/simplifiable_if_statement.py b/pylint/test/functional/simplifiable_if_statement.py
new file mode 100644
index 0000000..48d6dbb
--- /dev/null
+++ b/pylint/test/functional/simplifiable_if_statement.py
@@ -0,0 +1,120 @@
+"""Test that some if statement tests can be simplified."""

+

+# pylint: disable=missing-docstring, invalid-name

+

+

+def test_simplifiable_1(arg):

+    # Simple test that can be replaced by bool(arg)

+    if arg: # [simplifiable-if-statement]

+        return True

+    else:

+        return False

+

+

+def test_simplifiable_2(arg, arg2):

+    # Can be reduced to bool(arg and not arg2)

+    if arg and not arg2: # [simplifiable-if-statement]

+        return True

+    else:

+        return False

+

+

+def test_simplifiable_3(arg, arg2):

+    # Can be reduced to bool(arg and not arg2)

+    if arg and not arg2: # [simplifiable-if-statement]

+        var = True

+    else:

+        var = False

+    return var

+

+

+def test_simplifiable_4(arg):

+    if arg:

+        var = True

+    else:

+        if arg == "arg1": # [simplifiable-if-statement]

+            return True

+        else:

+            return False

+    return var

+

+

+def test_not_necessarily_simplifiable_1(arg, arg2):

+    # Can be reduced to bool(not arg and not arg2) or to

+    # `not all(N)`, which is a bit harder to understand

+    # than `any(N)` when var should be False.

+    if arg or arg2:

+        var = False

+    else:

+        var = True

+    return var

+

+

+def test_not_necessarily_simplifiabile_2(arg):

+    # This could theoretically be reduced to `not arg or arg > 3`

+    # but the net result is that now the condition is harder to understand,

+    # because it requires understanding of an extra clause:

+    #   * first, there is the negation of truthness with `not arg`

+    #   * the second clause is `arg > 3`, which occurs when arg has a

+    #     a truth value, but it implies that `arg > 3` is equivalent

+    #     with `arg and arg > 3`, which means that the user must

+    #     think about this assumption when evaluating `arg > 3`.

+    #     The original form is easier to grasp.

+    if arg and arg <= 3:

+        return False

+    else:

+        return True

+

+

+def test_not_simplifiable_3(arg):

+    if arg:

+        test_not_necessarily_simplifiabile_2(arg)

+        test_not_necessarily_simplifiable_1(arg, arg)

+        return False

+    else:

+        if arg < 3:

+            test_simplifiable_3(arg, 42)

+        return True

+

+

+def test_not_simplifiable_4(arg):

+    # Not interested in multiple elifs

+    if arg == "any":

+        return True

+    elif test_not_simplifiable_3(arg) == arg:

+        return True

+    else:

+        return False

+

+

+def test_not_simplifiable_5(arg):

+    # Different actions in each branch

+    if arg == "any":

+        return True

+    else:

+        var = 42

+    return var

+

+

+def test_not_simplifiable_6(arg):

+    # Different actions in each branch

+    if arg == "any":

+        var = 42

+    else:

+        return True

+    return var

+

+def test_not_simplifiable_7(arg):

+    # Returning something different

+    if arg == "any":

+        return 4

+    else:

+        return 5

+

+

+def test_not_simplifiable_8(arg):

+    # Only one of the branch returns something boolean

+    if arg == "any":

+        return True

+    else:

+        return 0

diff --git a/pylint/test/functional/simplifiable_if_statement.txt b/pylint/test/functional/simplifiable_if_statement.txt
new file mode 100644
index 0000000..74bdd16
--- /dev/null
+++ b/pylint/test/functional/simplifiable_if_statement.txt
@@ -0,0 +1,4 @@
+simplifiable-if-statement:8:test_simplifiable_1:The if statement can be reduced by returning bool of test

+simplifiable-if-statement:16:test_simplifiable_2:The if statement can be reduced by returning bool of test

+simplifiable-if-statement:24:test_simplifiable_3:The if statement can be reduced by assigning bool of test

+simplifiable-if-statement:35:test_simplifiable_4:The if statement can be reduced by returning bool of test
\ No newline at end of file