[prateekbhujel]

Description

As reported by Mukonda Kangwa on the PHP internals mailing list (https://externals.io/message/132904), running configure out-of-tree against a read-only source tree attempts to write main/php_config.h.in.tmp into $srcdir, fails with a filesystem error, and still exits with status 0.

Specifically, PHP_PATCH_CONFIG_HEADERS in build/php.m4 previously executed:

$SED -e 's/^#undef PACKAGE_[^ ]*/\/\* & \*\//g' < $srcdir/$1 \
  > $srcdir/$1.tmp && mv $srcdir/$1.tmp $srcdir/$1

This causes three problems during out-of-tree builds:

1. It mutates $srcdir by writing $srcdir/$1.tmp and overwriting $srcdir/$1.
2. When $srcdir is read-only, the redirection fails (Read-only file system / Permission denied), and because configure does not check the exit status of the pipeline, configure continues and exits 0.
3. When the write to $srcdir/main/php_config.h.in fails on a fresh source tree or release tarball, config.status falls back to the unpatched $srcdir/main/php_config.h.in and emits #define PACKAGE_* macros into main/php_config.h, defeating the purpose of PHP_PATCH_CONFIG_HEADERS.

Fix

Autoconf's config.status resolves AC_CONFIG_HEADERS input templates in the build tree first (test -f "$ac_f") before falling back to $srcdir/$ac_f.

This change updates PHP_PATCH_CONFIG_HEADERS in build/php.m4 to:

1. Ensure the target parent directory exists in the build tree via AS_MKDIR_P(["$(AS_DIRNAME(["$1"]))"]) before writing, since AC_CONFIG_COMMANDS_PRE hooks cannot assume the target subdirectory already exists.
2. Read from "$srcdir/$1" and write "$1.tmp" -> "$1" in the current build directory, leaving $srcdir untouched during out-of-tree builds while preserving in-place behavior for in-tree builds ($srcdir = .).
3. Fail with AC_MSG_ERROR([failed to patch $1]) if generating or moving the patched header template fails.

Verification

• Verified in-tree configure and ./config.status execution.
• Verified out-of-tree configure with a read-only source tree (chmod -R a-w as an unprivileged user): $srcdir remains unmodified, main/php_config.h.in and main/php_config.h are generated in the build tree with /* #undef PACKAGE_* */, and rerunning ./config.status preserves the patched output.
• Verified error propagation (configure: error: failed to patch ... with exit status 1) when template generation fails.
• Verified full CLI build (--disable-all --enable-cli --disable-cgi --disable-phpdbg --without-pear) and phpize extension configuration (both in-tree and out-of-tree with a read-only extension source directory).