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First session notes ‐ unhandled issues found

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Marcio Oliveira edited this page Aug 29, 2026 · 3 revisions

Just notes from my session fixing mbeddr.cpp tests and test environment:

A. Gaps/bugs found in mbeddr.cpp itself — not fixed, only worked around or deferred

  1. Generator: free function templates lose template on forward-declared prototypes — templates.mps, commit 0e88c30452. Blocks identity/compare/deref/multiplyBy and their tests; currently commented out.

  2. Generator: template classes with explicit constructors emit spurious, wrongly-qualified duplicate out-of-line definitions in the .cpp — same commit. Constructor-free template classes are unaffected, so this is specific to templates + explicit constructors.

  3. Generator: List/IntList template emission-order issue — same commit, same test area. No model-level workaround found; needs a real generator fix.

  4. Generator: global-using declarations are always emitted as a group ahead of every namespace declaration — namespaces.mps, commit c4b51ee1be. Invalid C++ when the referenced namespace lives in the same file. namespaceGlobalUsing test case commented out pending this.

  5. Nullptr_tType/CPPImplementationModule.importsForHeader() exists and works correctly but is never called from any generator template — nullPointers.mps, commit 62aa36dc3b. Result: (and any other computed std header) never reaches generated output, so std::nullptr_t fails to compile. Explicit TODO left in the commit: wire importsForHeader() into the header-generation template, then restore nullptr_t constructor/field/tests.

  6. Cross-module dependency scanner never emits an #include when a base class lives in another module — classes.mps, commit 0d9d456ee35. Traced to InheritanceInstance not extending TypeWithDeclaration. Worked around by reordering classes into the same module; commit explicitly says "no big changes were made to the language" and flags a need for a dedicated cross-module-inheritance test plus a real language-level fix.

  7. ArrayAttributeInitExpression textGen gap — same commit. Counter.value2 (an array field with this init form) was dropped rather than fixed; needs a textGen rule implementation.

  8. BuildConfiguration-generation-order bug: class visibility sections only generate correctly for pre-existing BuildConfigurations — thisPointer.mps, commit 0845d07b4e. Root cause never isolated ("persisted after trying different experiments"); content commented out rather than fixed.

  9. Constructor initializer lists can directly initialize an inherited field (invalid C++) — the language permits modeling it (permissive scope in ConstructorInitializedAttribute_Constraints) and the generator emits it verbatim with no correction (ConstructorInitializedAttribute_TextGen). The one place this was hit (constructor.mps, commit 020fa9739c) was fixed by reworking the test model, not by closing the underlying gap — the language still lets you model something the C++ generator can't emit correctly.

  10. Typesystem inconsistency: char literals can't initialize char16_t/char32_t/wchar_t globals, but the same types can be compared across each other — chars.mps, commit 80bc3b2026 fixed the editor-crashing NumberFormatException, but left 3 pre-existing ERROR-severity typesystem issues in place ("type char const volatile is not a subtype of ..."). Non-blocking (real g++ accepts the generated code) but a real subtyping-rule gap.

  11. Static.mps/specifier.mps deleted, not fixed — commit b0981b91f1. Used removed language concepts (e.g. StaticVar); root nodes stripped to unblock the rest of the suite. Recoverable from git history once those concepts are ported/replaced.

  12. testExTests doesn't fail the build when generated binaries/Makefiles silently go missing — the main recommendation from the earlier code review, explicitly deferred: "Until tests are not stable, I cannot fail the build when tests disappear."

  13. Shared PlatformTemplates default (-std=c++11) doesn't include -fpermissive — every existing test.ex module already had its own explicit override so this didn't need fixing there, but any newly created BuildConfiguration will silently need -fpermissive added by hand until either the template default is updated or item B below is fixed upstream.

B. Bug that lives in mbeddr (upstream), not mbeddr.cpp — only worked around here

  1. UnitTestUtil_boolToStr in mbeddr.core's bundled unit-test C runtime (com.mbeddr.core.unittest, languageAccessories/runtime.mps) returns C string literals ("true"/"false") from a function declared to return non-const char* — invalid C++ under any -std= version. This is why -fpermissive is permanently required in every test.ex BuildConfiguration, regardless of C++ standard. Confirmed unfixed and unchanged across mbeddr versions from 2022.3.26500.b633ef3 (what we vendor) through the newest 2026.1 branch. Not fixable from mbeddr.cpp — would need a fix or bug report upstream in mbeddr.core; once fixed, -fpermissive could potentially be dropped and -std=c++14+ revisited.

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