generate-configlist: collapse depfile for older Ninja

The tools/generate-configlist.sh script generates two files:
  * config-list.h
  * config-list.h.d

The former is included by the source code and the latter defines on
which files the former depends.

The contents of `config-list.h.d` consists of two sections:

    config-list.h: Documentation/config.adoc
    config-list.h: Documentation/git-config.adoc
    config-list.h: Documentation/config/add.adoc
    config-list.h: Documentation/config/advice.adoc
    config-list.h: Documentation/config/alias.adoc
    config-list.h: Documentation/config/am.adoc
    config-list.h: Documentation/config/apply.adoc
    ...

This first section actually defines on which individual files
`config-list.h` depends and thus needs to be rebuild if one of those
changes.

And the second section contains content like:

    Documentation/config.adoc:
    Documentation/git-config.adoc:
    Documentation/config/add.adoc:
    Documentation/config/advice.adoc:
    Documentation/config/alias.adoc:
    Documentation/config/am.adoc:
    Documentation/config/apply.adoc:
    ...

These rules exist to ensure Make won't fail with the following error if
one of the .adoc files is renamed or removed:

   make: *** No rule to make target 'Documentation/config.adoc', needed by 'config-list.h'.

With the no-op targets defined in `config-list.h.d`, Make knows there's
no work to be done to generate these files, so it doesn't error out if
it doesn't exist.

For the Makefile build system this works great. And since
ebeea3c471 (build: regenerate config-list.h when Documentation changes,
2026-02-24) this script is also called from the Meson build system.
Nevertheless, on AlmaLinux 8 the following build failure is seen:

    ninja: error: dependency cycle: config-list.h -> config-list.h

This version of this distro uses Ninja 1.8.2 and it seems to have some
issues with the format of the `config-list.h.d` file.

Ninja versions before 1.10.0 do not reset the depfile parser state on
newlines. This causes issues when the depfile has one dependency per
line, like we have in `config-list.h.d`:

    config-list.h: Documentation/config.adoc
    config-list.h: Documentation/config/add.adoc

The parser only recognizes the first "config-list.h:" as a target. On
subsequent lines it is still in dependency-parsing mode, so the repeated
output name is recorded as an input. This causes the error mentioned
above.

The bug in Ninja is fixed in 1.10, with commit
ninja-build/ninja@1daa7470ab7e (depfile_parser: remove restriction on
multiple outputs, 2019-11-20).

To be compatible with older versions of Ninja, collapse the dependencies
for `config-list.h` into a single line like:

    config-list.h: Documentation/config.adoc Documentation/config/add.adoc ...

This works around the bug in older versions of Ninja, and is fully
compatible Make and with more recent versions of Ninja. And while the
no-op targets are not needed for Ninja, they also don't do any harm.

Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Toon Claes <toon@iotcl.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/tools/generate-configlist.sh b/tools/generate-configlist.sh
index e28054f9e0e9bada23c3de046a047b6d6d69bfc2..d1d2ba4bb7fef900490422a4f1f55b1383ad5213 100755 (executable)
--- a/tools/generate-configlist.sh
+++ b/tools/generate-configlist.sh
@@ -42,9 +42,12 @@ if test -n "$DEPFILE"
 then
        QUOTED_OUTPUT="$(printf '%s\n' "$OUTPUT" | sed 's,[&/\],\\&,g')"
        {
+               printf '%s' "$QUOTED_OUTPUT: "
                printf '%s\n' "$SOURCE_DIR"/Documentation/*config.adoc \
                        "$SOURCE_DIR"/Documentation/config/*.adoc |
-                       sed -e 's/[# ]/\\&/g' -e "s/^/$QUOTED_OUTPUT: /"
+                       sed -e 's/[# ]/\\&/g' |
+                       tr '\n' ' '
+               printf '\n'
                printf '%s:\n' "$SOURCE_DIR"/Documentation/*config.adoc \
                        "$SOURCE_DIR"/Documentation/config/*.adoc |
                        sed -e 's/[# ]/\\&/g'