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C#: Update queries in Bad Practices/Implementation Hiding 
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‎change-notes/1.18/analysis-csharp.md‎

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| **Query** | **Tags** | **Purpose** |
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|-----------------------------|-----------|--------------------------------------------------------------------|
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| [Exposing internal representation (cs/expose-implementation)] | Different results | The query has been rewritten, based on the equivalent Java query. |
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| Local scope variable shadows member (cs/local-shadows-member) | maintainability, readability | Replaces the existing queries [Local variable shadows class member (cs/local-shadows-class-member)](https://help.semmle.com/wiki/display/CSHARP/Local+variable+shadows+class+member), [Local variable shadows struct member (cs/local-shadows-struct-member)](https://help.semmle.com/wiki/display/CSHARP/Local+variable+shadows+struct+member), [Parameter shadows class member (cs/parameter-shadows-class-member)](https://help.semmle.com/wiki/display/CSHARP/Parameter+shadows+class+member), and [Parameter shadows struct member (cs/parameter-shadows-struct-member)](https://help.semmle.com/wiki/display/CSHARP/Parameter+shadows+struct+member). |
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## Changes to existing queries

‎csharp/ql/src/Bad Practices/Implementation Hiding/AbstractToConcreteCollection.cs‎

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‎csharp/ql/src/Bad Practices/Implementation Hiding/AbstractToConcreteCollection.qhelp‎

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@@ -12,8 +12,8 @@ more difficult to change which implementation you are using at a later date.</p>
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</recommendation>
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<example>
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<p>The example shows casting from an ICollection to a List. This should be avoided where possible.</p>
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<sample src="AbstractToConcreteCollection.cs" />
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<p>The example shows casting from an <code>IEnumerable&lt;string&gt;</code> to a <code>List&lt;string&gt;</code>. This should be avoided where possible.</p>
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<sample src="AbstractToConcreteCollectionBad.cs" />
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</example>
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<references>

‎csharp/ql/src/Bad Practices/Implementation Hiding/AbstractToConcreteCollection.ql‎

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/**
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* @name Cast from abstract to concrete collection
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* @description Finds casts from an abstract collection to a concrete implementation
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* type. This makes the code brittle; it is best to program against the
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* abstract collection interfaces only.
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* @description A cast from an abstract collection to a concrete implementation type
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* makes the code brittle; it is best to program against the abstract
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* collection interface only.
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* @kind problem
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* @problem.severity warning
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* @precision medium
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* external/cwe/cwe-485
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*/
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import csharp
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import semmle.code.csharp.frameworks.system.Collections
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import semmle.code.csharp.frameworks.system.collections.Generic
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/** A sub-interface of Collection */
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/** A collection interface. */
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class CollectionInterface extends Interface {
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CollectionInterface() {
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exists(string name |
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this.getSourceDeclaration().getABaseType*().getName() = name and
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( name.matches("ICollection<%>")
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or name="ICollection")
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exists(Interface i |
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i = this.getABaseInterface*() |
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i instanceof SystemCollectionsICollectionInterface or
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i.getSourceDeclaration() instanceof SystemCollectionsGenericICollectionInterface or
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i instanceof SystemCollectionsIEnumerableInterface or
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i.getSourceDeclaration() instanceof SystemCollectionsGenericIEnumerableTInterface
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)
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}
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}
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from CastExpr e, Class c, CollectionInterface i
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where e.getType() = c and
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e.getExpr().getType().(RefType).getSourceDeclaration() = i
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select e, "Questionable cast from abstract " + i.getName()
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+ " to concrete implementation " + c.getName() + "."
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where e.getType() = c
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and e.getExpr().getType() = i
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and c.isImplicitlyConvertibleTo(i)
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select e, "Questionable cast from abstract '" + i.getName()
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+ "' to concrete implementation '" + c.getName() + "'."

‎csharp/ql/src/Bad Practices/Implementation Hiding/AbstractToConcreteCollectionBad.cs‎

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using System.Collections.Generic;
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class Bad
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{
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public static void Main(string[] args)
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{
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var names = GetNames();
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var list = (List<string>) names;
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list.Add("Eve");
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}
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static IEnumerable<string> GetNames()
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{
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var ret = new List<string>()
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{
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"Alice",
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"Bob"
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};
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return ret;
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}
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}

‎csharp/ql/src/Bad Practices/Implementation Hiding/ExposeRepresentation.cs‎

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‎csharp/ql/src/Bad Practices/Implementation Hiding/ExposeRepresentation.qhelp‎

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</recommendation>
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<example>
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<p>This example clearly demonstrates the problem with passing references to mutable objects outside a class. In this case
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it was possible to modify the values in the array despite the Range class not offering any method to do so.</p>
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<sample src="ExposeRepresentation.cs" />
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it was possible to modify the values in the array despite the <code>Range</code> class not offering any method to do so.</p>
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<sample src="ExposeRepresentationBad.cs" />
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</example>
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<section title="Fixing With an Immutable Object">
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<section title="Fixing with an immutable object">
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<p>Here the example has been modified to prevent changes to the private field by using a <code>ReadOnlyCollection</code>
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object.</p>
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<sample src="ExposeRepresentationFix1.cs" />
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<sample src="ExposeRepresentationGood1.cs" />
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</section>
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<section title="Fixing With Defensive Copying">
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<section title="Fixing with defensive copying">
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<p>This is an example of the same class but this time it returns a defensive copy of the private field. There is also
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a short program showing what happens when an attempt is made to modify the data held by the field.</p>
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<sample src="ExposeRepresentationFix2.cs" />
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<sample src="ExposeRepresentationGood2.cs" />
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</section>
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<references>
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<li>MSDN, C# Programming Guide, <a href="http://msdn.microsoft.com/en-us/library/vstudio/2z4khca9.aspx">Arrays as Objects</a>.</li>
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<li>MSDN, C# Programming Guide, <a href="https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/arrays/arrays-as-objects">Arrays as Objects</a>.</li>
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<li>MSDN, <a href="http://msdn.microsoft.com/en-us/library/ms132474.aspx">ReadOnlyCollection&lt;T&gt;</a>.</li>
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</references>

‎csharp/ql/src/Bad Practices/Implementation Hiding/ExposeRepresentation.ql‎

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/**
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* @name Exposes internal representation
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* @description Finds code that may expose an object's internal representation by
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* incorporating reference to mutable object.
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* @name Exposing internal representation
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* @description An object that accidentally exposes its internal representation may allow the
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* object's fields to be modified in ways that the object is not prepared to handle.
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* @kind problem
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* @problem.severity recommendation
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* @precision medium
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* @precision high
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* @id cs/expose-implementation
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* @tags reliability
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* external/cwe/cwe-485
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*/
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import csharp
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import semmle.code.csharp.commons.Collections
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import DataFlow
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/* This code stores a reference to an externally mutable object into the internal
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representation of the object.
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If instances are accessed by untrusted code, and unchecked changes to the mutable
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object would compromise security or other important properties,
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you will need to do something different. Storing a copy of the object is better
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approach in many situations.
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In this analysis an object is considered mutable if it is an array, a
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java.util.Hashtable, or a java.util.Date.
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The analysis detects stores to fields of these types where the value is given as a
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parameter. */
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from Assignment a, Field f, VariableAccess va, RefType t
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where a.getLValue() = va and
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va.getTarget() = f and
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f.getType().(RefType).getSourceDeclaration() = t and
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( (va.(MemberAccess).hasQualifier() and
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va.(MemberAccess).getQualifier() instanceof ThisAccess)
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or not va.(MemberAccess).hasQualifier()) and
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a.getRValue().(VariableAccess).getTarget() instanceof Parameter and
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( t instanceof ArrayType
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//Add mutable types here as necessary. Kept the java types as a reference
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/*or t.hasQualifiedName("java.util", "Hashtable")
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or t.hasQualifiedName("java.util", "Date")*/)
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select a,
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"May expose internal representation by storing an externally mutable object in "
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+ f.getName() + "."
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predicate storesCollection(Callable c, Parameter p, Field f) {
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f.getDeclaringType() = c.getDeclaringType().getABaseType*().getSourceDeclaration() and
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f.getType() instanceof CollectionType and
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p = c.getAParameter() and
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f.getAnAssignedValue() = p.getAnAccess() and
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not c.(Modifiable).isStatic()
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}
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predicate returnsCollection(Callable c, Field f) {
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f.getDeclaringType() = c.getDeclaringType().getABaseType*().getSourceDeclaration() and
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f.getType() instanceof CollectionType and
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c.canReturn(f.getAnAccess()) and
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not c.(Modifiable).isStatic()
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}
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predicate mayWriteToCollection(Expr modified) {
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modified instanceof CollectionModificationAccess
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or
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exists(Expr mid |
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mayWriteToCollection(mid) |
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localFlow(exprNode(modified), exprNode(mid))
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)
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or
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exists(MethodCall mid, Callable c |
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mayWriteToCollection(mid) |
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mid.getTarget() = c and
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c.canReturn(modified)
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)
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}
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predicate modificationAfter(Expr before, Expr after) {
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mayWriteToCollection(after) and
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localFlowStep+(exprNode(before), exprNode(after))
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}
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VariableAccess varPassedInto(Callable c, Parameter p) {
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exists(Call call |
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call.getTarget() = c |
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call.getArgumentForParameter(p) = result
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)
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}
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predicate exposesByReturn(Callable c, Field f, Expr why, string whyText) {
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returnsCollection(c, f) and
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exists(MethodCall ma |
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ma.getTarget() = c |
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mayWriteToCollection(ma) and
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why = ma and
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whyText = "after this call to " + c.getName()
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)
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}
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predicate exposesByStore(Callable c, Field f, Expr why, string whyText) {
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exists(VariableAccess v, Parameter p |
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storesCollection(c, p, f) and
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v = varPassedInto(c, p) and
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modificationAfter(v, why) and
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whyText = "through the variable " + v.getTarget().getName()
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)
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}
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from Callable c, Field f, Expr why, string whyText
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where exposesByReturn(c, f, why, whyText) or
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exposesByStore(c, f, why, whyText)
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select c, "'" + c.getName() + "' exposes the internal representation stored in field '" + f.getName() +
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"'. The value may be modified $@.",
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why.getLocation(), whyText

‎csharp/ql/src/Bad Practices/Implementation Hiding/ExposeRepresentationBad.cs‎

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using System;
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class Bad
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{
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class Range
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{
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private int[] rarray = new int[2];
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public Range(int min, int max)
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{
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if (min <= max)
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{
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rarray[0] = min;
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rarray[1] = max;
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}
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}
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public int[] Get() => rarray;
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}
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public static void Main(string[] args)
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{
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var r = new Range(1, 10);
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var r_range = r.Get();
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r_range[0] = 500;
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Console.WriteLine("Min: " + r.Get()[0] + " Max: " + r.Get()[1]);
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// prints "Min: 500 Max: 10"
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}
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}

‎csharp/ql/src/Bad Practices/Implementation Hiding/ExposeRepresentationFix1.cs‎

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