V8 CRTP regression: NDK r27+ (Clang 18+) fails to compile turboshaft on v26.x

[Towartz]

Problem

NDK r27+ ships Clang 18+, which introduces a CRTP (Curiously Recurring Template Pattern) name-lookup regression in V8's turboshaft AssemblerOpInterface<Next> : public Next.

Error signature

../deps/v8/src/compiler/turboshaft/assembler.h:1549:24: error: member initializer 'matcher_' does not name a non-static data member or base class
../deps/v8/src/compiler/turboshaft/assembler.h:1551:52: error: use of undeclared identifier 'matcher_'
../deps/v8/src/compiler/turboshaft/assembler.h:1557:12: error: use of undeclared identifier 'ReduceIfReachableTypeHint'
...
fatal error: too many errors emitted, stopping now [-ferror-limit=]

Root cause

Clang 18+ requires this-> qualification for dependent names in templated base classes (CRTP). V8's AssemblerOpInterface<Next> : public Next uses unqualified names like matcher_, ReduceIfReachable*, resolve() in macros and constructor initializer lists. These worked with Clang 17 but fail with Clang 18+.

The affected code is in deps/v8/src/compiler/turboshaft/assembler.h — the DECL_MULTI_REP_BINOP_V, DECL_MULTI_REP_BINOP, and related macros, plus the constructor initializer list at line ~1549.

Current workaround

Use NDK r26d (Clang 17) — the last NDK release without this regression.

• main branch (v26.x): pinned to r26d
• build_ndkr27 branch (v24.x LTS): uses r27d (v24.x's V8 turboshaft is unaffected)

What needs to be done

1. Upstream fix in V8: add this-> to all dependent names in AssemblerOpInterface. This is a V8-side change tracked at build: update android-patches/trap-handler.h.patch nodejs/node#60369.
2. Monitor Node.js/V8 releases for a backported fix. Once available, we can upgrade NDK and remove the r26d pin.
3. Investigate whether a targeted patch (adding this-> only where needed) is feasible and stable enough to carry until the upstream fix lands.

Related

• build: update android-patches/trap-handler.h.patch nodejs/node#60369
• Incorrect selection of x64 push_registers_asm.cc for host build when target is arm (Android) nodejs/node#58975
• build: commit some android build and test fixtures nodejs/node#57748

[Towartz]

Update: the issue is NOT Clang 18+ specific. It also reproduces with Clang 17 (NDK r26d) in C++20 mode. Root cause is two-phase name lookup — AssemblerOpInterface<Next> : public Next uses ReduceIfReachable*, matcher_, and resolve without this-> qualification, which fails in C++20 mode.

Current fix (commit 0e06528):

• Patch define-assembler-macros.inc: this->ReduceIfReachable##operation(, this->resolve(...) in macro definitions
• Patch assembler.h: this->ReduceIfReachable blanket replacement, this->matcher_ in init list and getter

Build running at https://github.com/Towartz/nodejs-arm/actions