# HG changeset patch
# User Adrian Buehlmann <adrian@cadifra.com>
# Date 1290336747 -3600
# Node ID 53391819f1958dfc1ad6b04e3b408c9842eabb03
# Parent  da69a1597285fe25eeedab1a45869487773b715b
check-code: catch Python 'is' comparing number or string literals

The Python 'is' operator compares object identity, so it should
definitely not be applied to string or number literals, which Python
implementations are free to represent with a temporary object.

This should catch the following kinds of bogus expressions (examples):

  x is 'foo'     x is not 'foo'
  x is "bar"     x is not "bar"
  x is 42        x is not 42
  x is -36       x is not -36

As originally proposed by Martin Geisler, amended with catching
negative numbers.

diff -r da69a1597285 -r 53391819f195 contrib/check-code.py
--- a/contrib/check-code.py	Sun Nov 21 13:16:59 2010 +0100
+++ b/contrib/check-code.py	Sun Nov 21 11:52:27 2010 +0100
@@ -149,6 +149,7 @@
     (r'raise Exception', "don't raise generic exceptions"),
     (r'ui\.(status|progress|write|note|warn)\([\'\"]x',
      "warning: unwrapped ui message"),
+    (r' is\s+(not\s+)?["\'0-9-]', "object comparison with literal"),
 ]
 
 pyfilters = [
diff -r da69a1597285 -r 53391819f195 tests/test-check-code.t
--- a/tests/test-check-code.t	Sun Nov 21 13:16:59 2010 +0100
+++ b/tests/test-check-code.t	Sun Nov 21 11:52:27 2010 +0100
@@ -52,3 +52,44 @@
    >     y = format(x)
    any/all/format not available in Python 2.4
   [1]
+
+  $ cat > is-op.py <<EOF
+  > # is-operator comparing number or string literal
+  > x = None
+  > y = x is 'foo'
+  > y = x is "foo"
+  > y = x is 5346
+  > y = x is -6
+  > y = x is not 'foo'
+  > y = x is not "foo"
+  > y = x is not 5346
+  > y = x is not -6
+  > EOF
+
+  $ "$check_code" ./is-op.py
+  ./is-op.py:3:
+   > y = x is 'foo'
+   object comparison with literal
+  ./is-op.py:4:
+   > y = x is "foo"
+   object comparison with literal
+  ./is-op.py:5:
+   > y = x is 5346
+   object comparison with literal
+  ./is-op.py:6:
+   > y = x is -6
+   object comparison with literal
+  ./is-op.py:7:
+   > y = x is not 'foo'
+   object comparison with literal
+  ./is-op.py:8:
+   > y = x is not "foo"
+   object comparison with literal
+  ./is-op.py:9:
+   > y = x is not 5346
+   object comparison with literal
+  ./is-op.py:10:
+   > y = x is not -6
+   object comparison with literal
+  [1]
+