/**

* @name Hashed value without GetHashCode definition

* @description Finds uses of hashing on types that define 'Equals(...)' but not 'GetHashCode()'.

* @kind problem

* @problem.severity warning

* @precision high

* @id cs/gethashcode-is-not-defined

* @tags quality

* reliability

* correctness

*/

import csharp

import semmle.code.csharp.frameworks.System

import semmle.code.csharp.frameworks.system.Collections

import semmle.code.csharp.frameworks.system.collections.Generic

/**

* Holds if `t` is a dictionary type.

*/

predicate dictionary(ValueOrRefType t) {

exists(Type base | base = t.getABaseType*().getUnboundDeclaration() |

base instanceof SystemCollectionsGenericIDictionaryInterface or

base instanceof SystemCollectionsGenericIReadOnlyDictionaryInterface or

base instanceof SystemCollectionsIDictionaryInterface

)

}

/**

* Holds if `c` is a hashset type.

*/

predicate hashSet(ValueOrRefType t) {

t.getABaseType*().getUnboundDeclaration() instanceof SystemCollectionsGenericHashSetClass

}

predicate hashStructure(Type t) { dictionary(t) or hashSet(t) }

/**

* Holds if the expression `e` relies on `GetHashCode()` implementation.

* That is, if the call assumes that `e1.Equals(e2)` implies `e1.GetHashCode() == e2.GetHashCode()`.

*/

predicate usesHashing(Expr e) {

exists(MethodCall mc, string name |

name = ["Add", "Contains", "ContainsKey", "Remove", "TryAdd", "TryGetValue"] and

mc.getArgument(0) = e and

mc.getTarget().hasName(name) and

hashStructure(mc.getTarget().getDeclaringType())

)

or

exists(IndexerCall ic |

ic.getArgument(0) = e and

dictionary(ic.getTarget().getDeclaringType())

)

}

predicate eqWithoutHash(RefType t) {

t.getAMethod() instanceof EqualsMethod and

not t.getAMethod() instanceof GetHashCodeMethod

}

predicate hashCall(Expr e) {

exists(MethodCall mc |

mc.getQualifier() = e and

mc.getTarget() instanceof GetHashCodeMethod

)

}

from Expr e, Type t

where

(usesHashing(e) or hashCall(e)) and

e.getType() = t and

eqWithoutHash(t)

select e,

"This expression is hashed, but type '" + t.getName() +

"' only defines Equals(...) not GetHashCode()."