Issue #21629 has been updated by k0kubun (Takashi Kokubun). Subject changed from Ruby-3.4.7 fails to build using clang / llvm to Ruby-3.4.7 prints -Wdefault-const-init-field-unsafe warnings on clang / llvm21 Status changed from Feedback to Open Backport changed from 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN to 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: REQUIRED To me, the direct cause of the build failure seems to be `-Werror` added by your environment. I don't know what part of llvm-21 or darwin-16 on Intel Mac leads to adding `-Werror`, but it's unfortunately normal that new compiler versions show warnings on Ruby builds, so you shouldn't let warnings fail your Ruby build. I'll repurpose this ticket for fixing the `-Wdefault-const-init-field-unsafe` warning. But the fact that you have `-Werror` in your build environment seems like a separate problem. ---------------------------------------- Bug #21629: Ruby-3.4.7 prints -Wdefault-const-init-field-unsafe warnings on clang / llvm21 https://bugs.ruby-lang.org/issues/21629#change-114789 * Author: debo (David Bohman) * Status: Open * ruby -v: ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x86_64-darwin16] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: REQUIRED ---------------------------------------- Here is the error I encountered. This is using clang version 21.1.3 as the compiler toolchain on Darwin. ``` DYLD_LIBRARY_PATH=.:../../.. ASAN_OPTIONS=detect_leaks=0 "clang -I../../../.ext/include/x86_64-darwin16 -I../../../../ruby-3.4.7/include -I../../../../ruby-3.4.7/ext/-test-/public_header_warnings -I/usr/local/include -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -D_DARWIN_UNLIMITED_SELECT -D_REENTRANT -fstack-protector-strong -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fdeclspec -O3 -fno-fast-math -ggdb3 -Wall -Wextra -Wextra-tokens -Wdeprecated-declarations -Wdivision-by-zero -Wdiv-by-zero -Wimplicit-function-declaration -Wimplicit-int -Wpointer-arith -Wshorten-64-to-32 -Wwrite-strings -Wold-style-definition -Wmissing-noreturn -Wno-cast-function-type -Wno-constant-logical-operand -Wno-long-long -Wno-missing-field-initializers -Wno-overlength-strings -Wno-parentheses-equality -Wno-self-assign -Wno-tautological-compare -Wno-unused-parameter -Wno-unused-value -Wunused-variable -Wmisleading-indentation -Wundef -fno-common -pipe -D_TEST_OK -Werror -c conftest.c" In file included from conftest.c:1: In file included from ../../../../ruby-3.4.7/include/ruby.h:38: In file included from ../../../../ruby-3.4.7/include/ruby/ruby.h:28: In file included from ../../../../ruby-3.4.7/include/ruby/internal/arithmetic.h:24: In file included from ../../../../ruby-3.4.7/include/ruby/internal/arithmetic/char.h:29: ../../../../ruby-3.4.7/include/ruby/internal/core/rstring.h:398:24: error: default initialization of an object of type 'struct RString' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe] 398 | struct RString retval; | ^ ../../../../ruby-3.4.7/include/ruby/internal/core/rbasic.h:86:17: note: member 'klass' declared 'const' here 86 | const VALUE klass; | ^ 1 error generated. checked program was: /* begin */ 1: #include "ruby.h" 2: 3: int main(int argc, char **argv) 4: { 5: return !!argv[argc]; 6: } /* end */ ``` The configuration is the following: ``` CC=clang CXX=clang++ CPPFLAGS=-I/usr/local/include LDFLAGS=-L/usr/local/lib ../ruby-3.4.7/configure --enable-shared --with-rdoc=ri,html ``` ---Files-------------------------------- ruby-log.txt (432 KB) ruby-log-2.txt (372 KB) -- https://bugs.ruby-lang.org/