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Python: Document IsComparisons.qll.

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Taus Brock-Nannestad
2020-06-23 14:30:17 +02:00
parent d6e5a5cb01
commit 2f93b1458e
1 changed files with 13 additions and 0 deletions
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13
python/ql/src/Expressions/IsComparisons.qll
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@@ -1,5 +1,8 @@
/** INTERNAL - Helper predicates for queries concerning comparison of objects using `is`. */
import python
/** Holds if `comp` uses `is` or `is not` (represented as `op`) to compare its `left` and `right` arguments. */
predicate comparison_using_is(Compare comp, ControlFlowNode left, Cmpop op, ControlFlowNode right) {
exists(CompareNode fcomp | fcomp = comp.getAFlowNode() |
fcomp.operands(left, op, right) and
@@ -7,6 +10,7 @@ predicate comparison_using_is(Compare comp, ControlFlowNode left, Cmpop op, Cont
)
}
/** Holds if the class `c` overrides the default notion of equality or comparison. */
predicate overrides_eq_or_cmp(ClassValue c) {
major_version() = 2 and c.hasAttribute("__eq__")
or
@@ -19,12 +23,14 @@ predicate overrides_eq_or_cmp(ClassValue c) {
major_version() = 2 and c.hasAttribute("__cmp__")
}
/** Holds if the class `cls` is likely to only have a single instance throughout the program. */
predicate probablySingleton(ClassValue cls) {
strictcount(Value inst | inst.getClass() = cls) = 1
or
cls = Value::named("None").getClass()
}
/** Holds if using `is` to compare instances of the class `c` is likely to cause unexpected behavior. */
predicate invalid_to_use_is_portably(ClassValue c) {
overrides_eq_or_cmp(c) and
// Exclude type/builtin-function/bool as it is legitimate to compare them using 'is' but they implement __eq__
@@ -35,6 +41,7 @@ predicate invalid_to_use_is_portably(ClassValue c) {
not probablySingleton(c)
}
/** Holds if `f` points to either `True`, `False`, or `None`. */
predicate simple_constant(ControlFlowNode f) {
exists(Value val | f.pointsTo(val) |
val = Value::named("True") or val = Value::named("False") or val = Value::named("None")
@@ -66,10 +73,12 @@ private predicate universally_interned_value(Expr e) {
e.(StrConst).getText() = ""
}
/** Holds if the expression `e` points to an interned constant in CPython. */
predicate cpython_interned_constant(Expr e) {
exists(Expr const | e.pointsTo(_, const) | cpython_interned_value(const))
}
/** Holds if the expression `e` points to a value that can be reasonably expected to be interned across all implementations of Python. */
predicate universally_interned_constant(Expr e) {
exists(Expr const | e.pointsTo(_, const) | universally_interned_value(const))
}
@@ -92,6 +101,10 @@ private predicate comparison_one_type(Compare comp, Cmpop op, ClassValue cls) {
)
}
/**
* Holds if the comparison `comp` (with operator `op`) is an invalid comparison using `is` or `is not`
* when applied to instances of the class `cls`.
*/
predicate invalid_portable_is_comparison(Compare comp, Cmpop op, ClassValue cls) {
// OK to use 'is' when defining '__eq__'
not exists(Function eq | eq.getName() = "__eq__" or eq.getName() = "__ne__" |