[mborland]

This PR fixes references initialized from a reference whose referent is not known. This only impacted C++26 mode for reference parameters and for local references. Also now properly errors in C++26 mode when used in constant expressions.

Summary by CodeRabbit

• Bug Fixes
  • Corrected constant-expression handling for references whose referent cannot be determined at compile time. Such initializations are now rejected where a constant expression is required, including affected constexpr declarations in C++23 and C++26 modes.
  • This also applies to references in aggregates and references initialized from parameters or external references.

[coderabbitai]

No actionable comments were generated in the recent review.

Walkthrough

The constant-folding check now rejects constants that address unknown objects. Regression tests cover reference initialization in C++23 and C++26, including runtime cases and constexpr initializations that produce errors.

Changes: Reference initialization

Layer / File(s)	Summary
Unknown-object detection src/il.h, src/il.c, src/decl_inits.c	A new helper detects addresses of unknown objects in constants. The initializer check uses it to exclude matching constants from the folded-initializer path.
Runtime reference cases tests/tests/regressions/gh-525.sft.cpp, tests/tests/regressions/.gh-525.rto/*	The regression test covers reference parameters, structured bindings, aggregate and external references, and other reference cases. Fixtures run the test in C++23 and C++26 modes.
Constant-expression diagnostics tests/tests/regressions/gh-525-negative.sft.cpp, tests/tests/regressions/.gh-525-negative.rto/*, tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/*, tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-p2280r4.rto/*, src/pending_changes/gh-525-reference-to-unknown-reference.txt	Negative tests and expected outputs cover rejected constexpr reference initializations. Imported diagnostic baselines also record changed constant-expression results. The pending-change note describes the affected cases.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Possibly related issues

• C++26: A reference bound to a reference parameter is wrong #525 — The reported reference-binding behavior and C++26 mode match the reference-parameter and unknown-referent cases covered by this change.

Suggested reviewers: nv-cmeerw, daveedvdv-nvidia

Merge Risk: Minimal · up to 78f9f

The change makes references initialized from a reference parameter bind to the right object, and it reports an error when such an initializer is used in a C++26 constant expression. No concrete merge-blocking risk remains. The regression tests and updated diagnostic baselines cover both the runtime and the rejected cases.

Pre-merge checks: 4

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title names the main change: fixing C++26 reference initialization when the initializing reference refers to an unknown object (reference parameter), tied to issue GH #525. The summary shows the c…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title names the main change: fixing C++26 reference initialization when the initializing reference refers to an unknown object (reference parameter), tied to issue GH #525. The summary shows the core change is a new check, constant_addresses_unknown_object, that rejects such initializers in the constant-folding branch, plus tests and a pending-changes note for that behavior. The title matches the changeset and does not claim unrelated work.

Finishing Touches

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Recent review info

Run configuration

• Source mode: Auto
• Repository: edgcpp/compiler
• Branch: main
• File: .coderabbit.yaml
• Commit: 63d8840
• Layers: Repository YAML
• Review profile: CHILL
• Plan: Advanced
• Run ID: 6d338525-1f54-410b-88ae-bcee4cc833ed

Commits

Reviewing files that changed from the base of the PR and between 341b1c2 and 78f9fbd.

Files selected for processing: 25

• src/decl_inits.c
• src/il.c
• src/il.h
• src/pending_changes/gh-525-reference-to-unknown-reference.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/default.1.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/default.2.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/default.3.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/edg_x86_32.1.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/edg_x86_32.2.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/edg_x86_32_cp.1.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/edg_x86_32_cp.2.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/edg_x86_32_cp.3.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/edg_x86_64_cp.1.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/edg_x86_64_cp.2.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-cxx11.rto/edg_x86_64_cp.3.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-p2280r4.rto/default.1.1.txt
• tests/tests/imported/clang/cpp/SemaCXX/.constant-expression-p2280r4.rto/default.2.1.txt
• tests/tests/regressions/.gh-525-negative.rto/default.1.1.txt
• tests/tests/regressions/.gh-525-negative.rto/default.2.1.txt
• tests/tests/regressions/.gh-525.rto/default.1.1.txt
• tests/tests/regressions/.gh-525.rto/default.1.2.txt
• tests/tests/regressions/.gh-525.rto/default.2.1.txt
• tests/tests/regressions/.gh-525.rto/default.2.2.txt
• tests/tests/regressions/gh-525-negative.sft.cpp
• tests/tests/regressions/gh-525.sft.cpp

Files skipped from review as they are similar to previous changes: 1

• src/pending_changes/C++26: A reference bound to a reference parameter is wrong #525-reference-to-unknown-reference.txt

Included review availability: This review used your included allowance. Your plan provides up to 4 included reviews per hour; 3 remain after this review.

[edgcpp-bot]

AcknowlEDG review results updated for 341b1c2757ce:

• Test - Changes (new)

[edgcpp-bot]

AcknowlEDG review results updated for 341b1c2757ce:

• Bench - C (new)
• Bench - C++ (new)
• Test - Changes (unchanged)
• Test - Failures (new)

CI failure.

[edgcpp-bot]

AcknowlEDG review results updated for 78f9fbd67e30:

• Bench - C (unchanged)
• Bench - C++ (unchanged)
• Test - Changes (updated)
• Test - Failures (unchanged)

[edgcpp-bot]

AcknowlEDG review results updated for 78f9fbd67e30:

• Bench - C (updated)
• Bench - C++ (updated)
• Test - Changes (unchanged)
• Test - Failures (no longer applies)

CI success.