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build: Disable -Wbraced-scalar-init, which is incompatible with -Wc++11-narrowing#23191

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build: Disable -Wbraced-scalar-init, which is incompatible with -Wc++11-narrowing#23191
maflcko wants to merge 1 commit intobitcoin:masterfrom
maflcko:2110-buildW

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@maflcko
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@maflcko maflcko commented Oct 5, 2021

To test:

void Fun(int) {}
int main() {
    unsigned a(-1);
    Fun({a});
}

Before:

$ clang++ -Wbraced-scalar-init -Wc++11-narrowing -std=c++17 /tmp/1.cpp -o /tmp/exe 
/tmp/1.cpp:4:10: error: non-constant-expression cannot be narrowed from type 'unsigned int' to 'int' in initializer list [-Wc++11-narrowing]
    Fun({a});
         ^
/tmp/1.cpp:4:10: note: insert an explicit cast to silence this issue
    Fun({a});
         ^
         static_cast<int>( )
/tmp/1.cpp:4:9: warning: braces around scalar initializer [-Wbraced-scalar-init]
    Fun({a});
        ^~~
1 warning and 1 error generated.

After:

$ clang++ -Wno-braced-scalar-init -Wc++11-narrowing -std=c++17 /tmp/1.cpp -o /tmp/exe 
/tmp/1.cpp:4:10: error: non-constant-expression cannot be narrowed from type 'unsigned int' to 'int' in initializer list [-Wc++11-narrowing]
    Fun({a});
         ^
/tmp/1.cpp:4:10: note: insert an explicit cast to silence this issue
    Fun({a});
         ^
         static_cast<int>( )
1 error generated.

@practicalswift
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practicalswift commented Oct 5, 2021 •
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Concept ACK

@vasild
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vasild commented Oct 5, 2021

Why is it incompatible? In the output above there is 1 error due to Wc++11-narrowing and 1 warning due to Wbraced-scalar-init. When the latter is disabled the warning is not shown. I don't see the relation (incompatibility) between the two options.

OTOH, F({a}) looks wrong, I would like the compiler to point it to me so that I can fix it to F(a), no?

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vasild commented Oct 5, 2021

Is the intention to use F({a}) with Wc++11-narrowing to get a warning for passing "incompatible" types? Could the same be achieved by F(a) with Wimplicit-int-conversion and/or Wsign-conversion?

@maflcko
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maflcko commented Oct 5, 2021

OTOH, F({a}) looks wrong, I would like the compiler to point it to me so that I can fix it to F(a), no?

F(a) will disable -Wc++11-narrowing.

@maflcko
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maflcko commented Oct 5, 2021

Could the same be achieved by F(a) with Wimplicit-int-conversion and/or Wsign-conversion?

It is currently not possible to compile Bitcoin Core with either of those settings.

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DrahtBot commented Oct 6, 2021 •
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The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Conflicts

Reviewers, this pull request conflicts with the following ones:

  • #23269 (build: remove redundant warning flags by fanquake)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

This was referenced Oct 7, 2021
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DrahtBot commented Oct 14, 2021

🐙 This pull request conflicts with the target branch and needs rebase.

Want to unsubscribe from rebase notifications on this pull request? Just convert this pull request to a "draft".

fanquake
fanquake reviewed Nov 16, 2021
View reviewed changes
configure.ac
AX_CHECK_COMPILE_FLAG([-Wself-assign],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-self-assign"],,[[$CXXFLAG_WERROR]])
AX_CHECK_COMPILE_FLAG([-Wunused-local-typedef],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-unused-local-typedef"],,[[$CXXFLAG_WERROR]])
dnl -Wbraced-scalar-init is incompatible with -Wc++11-narrowing
AX_CHECK_COMPILE_FLAG([-Wbraced-scalar-init],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-braced-scalar-init"],,[[$CXXFLAG_WERROR]])
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Suggested change
AX_CHECK_COMPILE_FLAG([-Wbraced-scalar-init],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-braced-scalar-init"],,[[$CXXFLAG_WERROR]])
AX_CHECK_COMPILE_FLAG([-Wbraced-scalar-init], [NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-braced-scalar-init"], [], [$CXXFLAG_WERROR])

@maflcko maflcko closed this Nov 17, 2021
@maflcko maflcko deleted the 2110-buildW branch November 17, 2021 19:23
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