Migrate IPR non-mutating headers to C++20 modules (includes and supersedes #322)#323
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Replace <ipr/interface> and its transitive header dependencies with a named C++20 module expressed as three partitions: cxx.ipr:vocabulary - structural templates, enums, locations cxx.ipr:syntax - tokens, attributes, declarators, constraints cxx.ipr - semantic node hierarchy, Visitor, Lexicon New files: src/cxx-ipr-vocabulary.ixx - :vocabulary partition src/cxx-ipr-syntax.ixx - :syntax partition src/cxx-ipr.ixx - primary module interface src/cxx-ipr.cxx - module implementation unit include/ipr/std-preamble - TEMPORARY standard header preamble include/ipr/utility-impl - impl-only utility types (rb_tree, etc.) Removed headers: interface, synopsis, ancillary, location, attribute, cxx-form, utility, and src/interface.cxx. Tested on MSVC 19.50, GCC 15.2, Clang 21.1 (libstdc++ and libc++).
Preserve the original form and content of comments that were inadvertently dropped or reformatted when migrating headers to C++20 module partitions: - cxx-ipr-syntax.ixx: restore '// -- ' prefix on the design rationale comment block (matching the original <ipr/cxx-form>) - cxx-ipr-vocabulary.ixx: restore box-style section dividers, add missing directive forward declarations section, add 'distinguished node' section, restore multi-line inline comments on Phantom, Demotion, and Label - cxx-ipr.cxx: add Visitor sub-hierarchy forwarding rationale and section headers (Types, Expressions, Directives, Statements, Declarations) from the original traversal.cxx - utility-impl: restore rb_tree algorithm comments (rotation operations, chain/container insert documentation, string pool description)
Introduce two new named modules:
- cxx.ipr.traversal: structural comparison, visitor utilities
- cxx.ipr.io: the XPR pretty-printer
Move physically_same and as<> from the traversal module to
cxx.ipr's :vocabulary partition, where they belong: both are
vocabulary-level predicates depending only on Node&.
New files:
- src/cxx-ipr-traversal.ixx (module interface)
- src/cxx-ipr-traversal.cxx (module implementation unit)
- src/cxx-ipr-io.ixx (module interface)
- src/cxx-ipr-io.cxx (module implementation unit)
Deleted files:
- include/ipr/traversal (replaced by cxx.ipr.traversal)
- include/ipr/io (replaced by cxx.ipr.io)
- src/traversal.cxx (renamed to cxx-ipr-traversal.cxx)
- src/io.cxx (renamed to cxx-ipr-io.cxx)
Key changes:
- Export physically_same and as<> from cxx.ipr:vocabulary.
This eliminates the as<> duplicate that was in cxx-ipr.cxx,
and removes the need for <ipr/impl> to import cxx.ipr.traversal.
- Define util::std_insertable solely in cxx.ipr.io (removed
from <ipr/utility-impl> where it was the only consumer).
- Both module interfaces import only cxx.ipr; implementation-
only dependencies (cxx.ipr.traversal in cxx-ipr-io.cxx,
<typeinfo> in cxx-ipr-traversal.cxx) are in the .cxx files.
- Update CMakeLists.txt: new module file sets, renamed sources,
removed deleted headers from PRIVATE list.
- Update consumer TUs: only files that use traversal-specific
symbols (Constant_visitor, util::view, etc.) import
cxx.ipr.traversal; others get physically_same from cxx.ipr.
Tested on:
- MSVC 19.50 (VS 18 Preview): pass
- GCC 15.2: pass
- Clang 21.1 (libstdc++): pass
- Clang 21.1 (libc++): pass
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GabrielDosReis
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Mar 17, 2026
cdacamar
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| // -*- C++ -*- | |||
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Summary
Migrate the IPR interface, traversal, and io headers to C++20 named modules. This PR includes and supersedes #322 (Migrate IPR interface to C++20 module
cxx.ipr), building on that work to also modularize<ipr/traversal>and<ipr/io>. Together, this completes the modularization of all non-mutating IPR components.Modules introduced
cxx.ipr(from PR Migrate IPR interface to C++20 module cxx.ipr #322) — the semantic node hierarchy, Visitor, Lexicon. Three partitions::vocabulary,:syntax, and the primary interface.cxx.ipr.traversal— structural comparison (structurally_same,denote_builtin_type), visitor adapters (Constant_visitor<F>,No_op,Missing_overrider), andutil::view<T>.cxx.ipr.io— the XPR pretty-printer:Printer,xpr_decl/xpr_stmt/xpr_type/xpr_expr, and theiroperator<<overloads.Key architectural decisions
physically_sameandas<>incxx.ipr:vocabulary. Both are vocabulary-level predicates depending only onNode&. This eliminates duplicates, removes the need for<ipr/impl>to importcxx.ipr.traversal, and avoids a GCC-rejected import cycle.util::std_insertabledefined solely incxx.ipr.io. Removed from<ipr/utility-impl>— single source of truth.Module interfaces import only
cxx.ipr. Implementation-only dependencies are in the.cxxfiles (minimize interface dependencies).Separate modules, not partitions for traversal and io — optional subsystems with distinct rates of change.
Testing
Documentation
reports/implementing-cxx-ipr-traversal-io.md— eight lessons learned during this migrationreports/implementing-cxx-ipr-module.md— lessons from thecxx.iprmigration (PR Migrate IPR interface to C++20 module cxx.ipr #322)reports/modularizing-traversal-and-io.md— architecture planreports/modularizing-ipr-interface.md— original architecture plan forcxx.ipr