Rust: Tweaks and improvements to data flow barriers

[paldepind]

• Adds a new barrier for fieldless enum types. Such enum are just a bunch of cases, so often they are not interesting to track.
• Split the boolean and numeric barriers apart. I think this scales better with more barriers (such as the above one).
• Add more barriers to a few queries. The boolean guard for cleartext logging in particular fixes some false results that I observed over on Rust: Lift content reads as taint steps #20879.

[Copilot]

Pull request overview

This PR refactors data flow barriers to improve specificity and reduce false positives in security queries. The main changes split combined barriers into separate, more specific ones, and add a new barrier type for fieldless enums.

• Refactors IntegralOrBooleanTypeBarrier into separate IntegralTypeBarrier and BooleanTypeBarrier classes for better granularity
• Introduces a new FieldlessEnumTypeBarrier to filter out fieldless enum types that are typically not interesting to track
• Applies these barriers to security queries (SQL injection, log injection, cleartext logging, and regex injection) to reduce false positives

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
rust/ql/lib/codeql/rust/security/Barriers.qll	Splits combined barriers into separate classes, adds FieldlessEnumTypeBarrier, and improves comment clarity
rust/ql/lib/codeql/rust/internal/Type.qll	Adds getEnum() accessor method to EnumType for consistency with other type classes
rust/ql/lib/codeql/rust/security/regex/RegexInjectionExtensions.qll	Updates to use separate IntegralTypeBarrier and BooleanTypeBarrier
rust/ql/lib/codeql/rust/security/SqlInjectionExtensions.qll	Adds BooleanTypeBarrier and FieldlessEnumTypeBarrier
rust/ql/lib/codeql/rust/security/LogInjectionExtensions.qll	Adds BooleanTypeBarrier and FieldlessEnumTypeBarrier
rust/ql/lib/codeql/rust/security/CleartextLoggingExtensions.qll	Adds Barriers import, BooleanTypeBarrier, and FieldlessEnumTypeBarrier

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