codeql/change-notes/1.18/analysis-csharp.md

Improvements to C# analysis

NOTES

Please describe your changes in terms that are suitable for customers to read. These notes will have only minor tidying up before they are published as part of the release notes.

General improvements

• Control flow analysis has been improved for catch clauses with filters.

New queries

Query	Tags	Purpose
Arbitrary file write during zip extraction ("Zip Slip") (cs/zipslip)	security, external/cwe/cwe-022	Identifies zip extraction routines which allow arbitrary file overwrite vulnerabilities.
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), Local variable shadows struct member (cs/local-shadows-struct-member), Parameter shadows class member (cs/parameter-shadows-class-member), and Parameter shadows struct member (cs/parameter-shadows-struct-member).

Changes to existing queries

Query	Expected impact	Change
Constant condition (cs/constant-condition)	More results	The query has been generalized to cover both Null-coalescing left operand is constant (cs/constant-null-coalescing) and Switch selector is constant (cs/constant-switch-selector).
Exposing internal representation (cs/expose-implementation)	Different results	The query has been rewritten, based on the equivalent Java query.
Local variable shadows class member(cs/local-shadows-class-member)	No results	The query has been replaced by Local scope variable shadows member (cs/local-shadows-member).
Local variable shadows struct member (cs/local-shadows-struct-member)	No results	The query has been replaced by Local scope variable shadows member (cs/local-shadows-member).
Missing Dispose call on local IDisposable (cs/local-not-disposed)	Fewer results	The query identifies more cases where the local variable may be disposed by a library call.
Nested loops with same variable (cs/nested-loops-with-same-variable)	Fewer results	Results are no longer highlighted in nested loops that share the same condition, and do not use the variable after the inner loop.
Null-coalescing left operand is constant (cs/constant-null-coalescing)	No results	The query has been removed, as it is now covered by Constant condition (cs/constant-condition).
Parameter shadows class member (cs/parameter-shadows-class-member)	No results	The query has been replaced by Local scope variable shadows member (cs/local-shadows-member).
Parameter shadows struct member (cs/parameter-shadows-struct-member)	No results	The query has been replaced by Local scope variable shadows member (cs/local-shadows-member).
Potentially incorrect CompareTo(...) signature (cs/wrong-compareto-signature)	Fewer results	Results are no longer highlighted in constructed types.
Switch selector is constant (cs/constant-switch-selector)	No results	The query has been removed, as it is now covered by Constant condition (cs/constant-condition).
Useless upcast (cs/useless-upcast)	Fewer results	The query has been improved to cover more cases where upcasts may be needed.

Changes to code extraction

• Series of bullet points

Changes to QL libraries

• A new non-member predicate mayBeDisposed() can be used to determine if a variable is potentially disposed inside a library. It will analyse the CIL code in the library to determine this.