Shared: Add Option types with location

[joefarebrother]

Adds to the shared library parameterised modules for Option types with location support.

Potential for bikeshedding on the names, especially LocOption2; unsure of a better name to describe its purpose.

LocOption requires a type that has a hasLocationInfo predicate, and LocOption2 requires a type with a getLocation predicate, and also needs to know about its result Location type.

This may be useful for queries with variable-length alert messages.
This is applicable to 2 in-flight PRs for Python quality queries (and is cherry-picked from one of them); these PRs will be rebased to depend on this one shortly: #20217, #19932.

I'm not that familiar with the use of parameterised modules, so if there are clearer ways to handle the implementation that I've missed, let me know.

[aschackmull]

What's with the B prefix? Is it meant to be shorthand for Base - in that case just use Base as a prefix - that's slightly clearer, I think. Alternatively, don't introduce final aliases at all - just use instanceof instead of extends, then we'll just need to repeat the 3 member methods with delegating super calls instead. I guess it's mostly a minor matter of style whether to go with extends final or instanceof.

[joefarebrother]

Yes, Base was the intention.
Using final aliases like this felt cleaner than repeating each method.

[aschackmull]

Let's use getLocation here instead of hasLocationInfo and rely on the existence of the empty Location - we do that plenty of other places.

[joefarebrother]

What's the canonical preferred way to refer to the empty location?
Is it l.hasLocationInfo("", 0, 0, 0, 0)

[aschackmull]

Yes. See e.g. git grep 'hasLocationInfo("", 0, 0, 0, 0)'.

[joefarebrother]

Suggestions applied.

[aschackmull]

Suggestions applied.

I'm not seeing any changes - did you forget to either commit or push?

[joefarebrother]

Whoops 😅
The latter.

[Copilot]

Pull Request Overview

This PR adds parameterized modules for Option types with location support to the shared library. The purpose is to provide Option types that can carry location information, which is useful for queries with variable-length alert messages.

• Adds OptionWithLocationInfo module for types with hasLocationInfo predicate
• Adds LocatableOption module for types with getLocation predicate
• Includes appropriate change notes documentation

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
shared/util/codeql/util/Option.qll	Adds two new parameterized modules with location support and required type signatures
shared/util/change-notes/2025-08-25-loc-option.md	Documents the addition of the new Option modules

[Copilot]

The None class incorrectly extends O::Some instead of O::None. This should be class None extends Option instanceof O::None { } to properly represent the None case.

Suggested change

	class None extends Option instanceof O::Some { }
	class None extends Option instanceof O::None { }

[hvitved]

Copilot is right; the two cases have been swapped.

[Copilot]

The Some class incorrectly extends O::None instead of O::Some. This should be class Some extends Option instanceof O::Some { } to properly represent the Some case.

Suggested change

	class None extends Option instanceof O::Some { }
	/** A wrapper for the given type. */
	class Some extends Option instanceof O::None { }
	class None extends Option instanceof O::None { }
	/** A wrapper for the given type. */
	class Some extends Option instanceof O::Some { }

[Copilot]

The None class incorrectly extends O::Some instead of O::None. This should be class None extends Option instanceof O::None { } to properly represent the None case.

Suggested change

	class None extends Option instanceof O::Some { }
	class None extends Option instanceof O::None { }

[hvitved]

Same.

[Copilot]

The Some class incorrectly extends O::None instead of O::Some. This should be class Some extends Option instanceof O::Some { } to properly represent the Some case.

Suggested change

	class None extends Option instanceof O::Some { }
	/** A wrapper for the given type. */
	class Some extends Option instanceof O::None { }
	class None extends Option instanceof O::None { }
	/** A wrapper for the given type. */
	class Some extends Option instanceof O::Some { }

[Copilot]

Copilot detected a code snippet with 13 occurrences. See search results for more details.

Matched Code Snippet

*
     * Holds if this element is at the specified location.
     * The location spans column `startColumn` of line `startLine` to
     * column `endColumn` of line `endLine` in file `filepath`.
     * For more information, see
     * [Providing locations in CodeQL queries](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
     */
    predicate hasLocationInfo(
      string filePath, int startLine, int

[hvitved]

Copilot is right; the two cases have been swapped.

[hvitved]

Same.

[aschackmull]

LGTM now.