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Write a header's definitions so it can be included from more than one translation unit [patch] - #457
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… translation unit [patch] A SourceFile marked IsHeader only gained #pragma once, so a free function, a function a method is lowered to, or a mutable file-scope variable in it was defined with external linkage in every translation unit that included it, and the program failed to link with "multiple definition". C++ now writes free functions and namespace-scope variables inline. C writes functions static inline and mutable variables static, one copy per translation unit, since C has no inline variable. Output that is not a header is unchanged. Fixes #423 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017vfJW4Rc5sqSEVHr6NgrkT
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Fixes #423
What was wrong
A
SourceFilewithIsHeader = trueonly gained#pragma once. That guard works within one translation unit but not across units. A header holding a free function, a function lowered from a method (C), or a mutable file-scope variable defined each one with external linkage in every unit that included it. Linking then failed withmultiple definition of 'twice','limit','P_get','geo::half(int)'and so on.Change
CFamilyGenerator.WritingHeaderreports whether the file being generated is a header. The C and C++ generators check it:inlinestatic inlinestatic inlineinline(C++17 inline variable)static: one copy per translation unitFor the C mutable global the issue offered two options. I chose
static, which is what the C generator already does for a type's static fields (static int P_count). The alternative,externplus a definition somewhere, would need a translation unit that a header-only output doesn't have. The choice is documented in the code and in CLAUDE.md.These stay as they were:
constexprand abstract functions in C++. These are already inline or have no definition.Tests
HeaderLinkageTestsbuilds a header with a mutable variable and a function at file scope, a struct with an instance method, a static method and a static field, and a namespace holding a variable and a function.-std=c11 -Wall -Wextra -pedantic-errors, C++ with-std=c++17 -Wall -Wextra -pedantic-errors.inline/static inline/static, and that output for a file that isn't a header is unchanged.I reverted the generator change and four of the five tests failed with the linker errors from the issue. With the change back in place the full suite passes: 1669 tests.
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