C++: Support alias templates#21860
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Add other missing cases to `isFromTemplateInstantiationRec` and `isFromUninstantiatedTemplateRec` while here.
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Pull request overview
This PR adds first-class CodeQL support for C++ alias templates and their instantiations. It introduces new dbscheme tables (is_alias_template, alias_instantiation, alias_template_argument, alias_template_argument_value), corresponding QL classes (TypeAliasType, AliasTemplateType, AliasTemplateInstantiationType), deprecates the existing UsingAliasTypedefType in favor of TypeAliasType, and wires alias templates into existing template-instantiation detection helpers.
Changes:
- Extend dbscheme with new alias-template relations and provide upgrade/downgrade scripts.
- Rename
UsingAliasTypedefTypetoTypeAliasType(deprecation stub kept) and addAliasTemplateType/AliasTemplateInstantiationType. - Teach
Element.qllandDeclaration.qllabout alias templates (and template-template parameters / concepts) for instantiation/argument lookup.
Show a summary per file
| File | Description |
|---|---|
| cpp/ql/lib/semmlecode.cpp.dbscheme | Adds new alias-template relations. |
| cpp/ql/lib/upgrades/770002bb02322e04fa25345838ce6e82af285a0b/{old.dbscheme,upgrade.properties} | Upgrade scaffolding for the dbscheme change. |
| cpp/downgrades/837c4e02326aee4582405d069263092e80a15d82/{semmlecode.cpp.dbscheme,upgrade.properties} | Downgrade to a scheme without the new relations. |
| cpp/ql/lib/semmle/code/cpp/TypedefType.qll | Introduces TypeAliasType/AliasTemplateType/AliasTemplateInstantiationType and deprecates UsingAliasTypedefType. |
| cpp/ql/lib/semmle/code/cpp/Element.qll | Includes alias templates (and template-template parameters/concepts) in template instantiation detection. |
| cpp/ql/lib/semmle/code/cpp/Declaration.qll | Exposes alias-template arguments via getTemplateArgument. |
| cpp/ql/lib/change-notes/2026-05-16-alias-template.md | New feature note. |
| cpp/ql/lib/change-notes/2026-05-18-alias-type.md | Deprecation note for UsingAliasTypedefType. |
| cpp/ql/test/library-tests/using-aliases/using-alias.expected | Updated to reflect renamed class. |
| cpp/ql/test/library-tests/ir/ir/PrintAST.expected | Updated to reflect renamed class. |
Copilot's findings
- Files reviewed: 14/15 changed files
- Comments generated: 4
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| int variable_id: @usertype ref, | ||
| int index: int ref, | ||
| int arg_type: @type ref | ||
| ); | ||
| alias_template_argument_value( | ||
| int variable_id: @usertype ref, |
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The name is not really relevant. I've another scheme update in the pipeline. I'll fix this as part of that update.
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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Introduce new classes exposing alias templates and their instantiations. While here, simplify the naming of type aliases.
Commit-by-commit reviewer recommended.