Remove static CladUtils AST caches

[Elvand-Lie]

Problem

Several CladUtils.cpp helpers cache Clang AST-owned declarations or types in function-local static variables:

• GetCladNamespace() cached NamespaceDecl*
• GetRestoreTrackerType() cached QualType
• GetCladMatrixOfType(), GetCladArrayOfType(), GetCladArrayRefOfType(), and GetCladTagOfType() cached TemplateDecl*

Those objects are tied to the current Sema / ASTContext. Reusing them across translation units in a long-lived process can leave stale AST pointers, similar to the LookupResult cache issue fixed in #1838.

Solution

Remove those function-local static caches and perform the lookup for the current Sema when needed.

Testing

• git diff --check HEAD

Local build was not run because this Windows environment does not have clang, llvm-config, cmake, or clang-format on PATH.

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[vgvassilev]

That patch essentially makes things slower. While it is right in its core that we can have multiple instances of clad in the same process it is not yet a practical use-case. An alternative approach would be to provide some per plugin instance cache area which is somehow shared with the rest of the infrastructure. I think overall it is not worth the effort and the complexity right now.

[github-actions]

clang-tidy made some suggestions

There were too many comments to post at once. Showing the first 10 out of 11. Check the log or trigger a new build to see more.

[github-actions]

warning: variable 'CachedCladNS' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]

    NamespaceDecl* CachedCladNS = nullptr;
                   ^

[github-actions]

warning: variable 'CachedCladNS' provides global access to a non-const object; consider making the pointed-to data 'const' [cppcoreguidelines-avoid-non-const-global-variables]

    NamespaceDecl* CachedCladNS = nullptr;
                   ^

[github-actions]

warning: variable 'CachedRestoreTrackerTy' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]

    QualType CachedRestoreTrackerTy;
             ^

[github-actions]

warning: variable 'CachedMatrixDecl' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]

    TemplateDecl* CachedMatrixDecl = nullptr;
                  ^

[github-actions]

warning: variable 'CachedMatrixDecl' provides global access to a non-const object; consider making the pointed-to data 'const' [cppcoreguidelines-avoid-non-const-global-variables]

    TemplateDecl* CachedMatrixDecl = nullptr;
                  ^

[github-actions]

warning: variable 'CachedArrayDecl' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]

    TemplateDecl* CachedArrayDecl = nullptr;
                  ^

[github-actions]

warning: variable 'CachedArrayDecl' provides global access to a non-const object; consider making the pointed-to data 'const' [cppcoreguidelines-avoid-non-const-global-variables]

    TemplateDecl* CachedArrayDecl = nullptr;
                  ^

[github-actions]

warning: variable 'CachedArrayRefDecl' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]

    TemplateDecl* CachedArrayRefDecl = nullptr;
                  ^

[github-actions]

warning: variable 'CachedArrayRefDecl' provides global access to a non-const object; consider making the pointed-to data 'const' [cppcoreguidelines-avoid-non-const-global-variables]

    TemplateDecl* CachedArrayRefDecl = nullptr;
                  ^

[github-actions]

warning: variable 'CachedTagDecl' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]

    TemplateDecl* CachedTagDecl = nullptr;
                  ^

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[Elvand-Lie]

@vgvassilev thanks again for the review. The first version was trying to avoid reusing AST-owned cached declarations/types across ASTContexts. After testing and looking at the hot path more carefully, I see why removing the caches entirely was the wrong tradeoff: it avoided stale pointers by making normal differentiation redo namespace/type/template lookups.

I reworked the PR to keep the cache fast path and reset the cached AST-owned values from CladPlugin::Initialize(ASTContext&). So the patch now keeps the cached NamespaceDecl*, QualType, and TemplateDecl* values, but clears them when a new plugin ASTContext is initialized.

Validation:

• local WSL Linux build of clad
• targeted lit suites: Arrays, ForwardMode, Gradient
• full local check-clad: 181 discovered, 158 passed, 23 unsupported, 0 failed
• GitHub CI is passing across the full matrix

I think this version addresses the practical stale-cache concern while preserving the existing performance model. If this still feels too narrow or not worth carrying right now, I am fine closing the PR.

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"