C#: Handle non-unique type arguments when computing generics strings

[hvitved]

Avoids a combinatorial explosion when type arguments are not unique.

[Copilot]

Pull Request Overview

This PR updates QL utilities to use monotonic aggregates and strictconcat when computing generic type argument strings, aiming to prevent combinatorial explosion for non-unique arguments.

• Enabled language[monotonicAggregates] for two helper functions
• Replaced direct getFullName/getName calls with strictconcat aggregators

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
csharp/ql/lib/semmle/code/csharp/commons/QualifiedName.qll	Added language[monotonicAggregates] and switched to strictconcat in getTypeArgumentsQualifiedName
csharp/ql/lib/semmle/code/csharp/Generics.qll	Added language[monotonicAggregates] and switched to strictconcat in getTypeArgumentName

Comments suppressed due to low confidence (2)

csharp/ql/lib/semmle/code/csharp/commons/QualifiedName.qll:54

• Using a strictconcat over a single-element generator tied to i doesn’t aggregate across all type arguments, so it won’t prevent combinatorial explosion. Consider removing the i parameter and aggregating over cg.getTypeArgument(*) in one call or moving the aggregation into the caller.

result = strictconcat(Type t | t = cg.getTypeArgument(i) | getFullName(t), "/")

csharp/ql/lib/semmle/code/csharp/Generics.qll:116

• This strictconcat is also scoped to a single i, so you’re effectively concatenating only one element. To handle non-unique arguments correctly, aggregate over all arguments at once rather than indexing per call.

result = strictconcat(Type t | t = cg.getTypeArgument(i) | t.getName(), "/")

[aschackmull]

Could we add comments stating that this is merely a precaution and that we expect he concat to only concat a single name.

[hvitved]

Done