std.Build.Step.ConfigHeader: Add support for Autoconf-style @FOO@ variables
#22794
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Add the new style `Style.autoconf_at`. Rename the existing `Style.autoconf` (which uses `#undef` directives) to `Style.autoconf_undef`.
cbilz
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Feb 9, 2025
There were a few configuration value conflicts between `config.h` and the Gnulib headers, so it made sense to draw their values from different pools. The Gnulib headers use `@FOO@`-style substitution hooks. So far, we used `ConfigHeader.Style.cmake` to configure these, but this fails for `unistd.h`, see ziglang/zig#22794. Further, we add a function that allows build-time configuration of `ConfigHeader` values, see ziglang/zig#22795. This is more convenient and should improve overall build times as comptime is still relatively slow. We use a modified version of `ConfigHeader` until these pull requests are merged.
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Autoconf configuration header templates often use
#undefdirectives as substitution hooks, which we already support viaConfigHeader.Style.autoconf. However, many projects, particularly those using Gnulib, additionally rely on@FOO@-style output variables for header configuration. While some of these cases can be handled usingStyle.cmake, this fails when the template happens to contain strings like${FOO}.For example, the Gnulib header template
lib/unistd.in.huses@FOO@-style substitutions, but also happens to contain the string${LOGNAME-$USER}in a code comment. This is misinterpreted as a substitution hook byStyle.cmake. Attempting to work around this by adding a value like.{ @."LOGNAME-$USER" = ... }toConfigHeaderfails becauseStyle.cmakerejects the invalid$character in the variable name.To resolve this issue, this pull request adds a new
Style.autoconf_atspecifically for@FOO@-style substitutions as used by Autoconf. Additionally,Style.autoconfis renamed toStyle.autoconf_undeffor clarity. The newStyle.autoconf_atis similar toStyle.cmake, but does not perform${}or#cmakedefinesubstitutions, enabling the correct configuration of headers like the one described above.