Implement a meta-check for ncurses detection

[BenBE]

This was inspired by a patch for OpenEmbedded:
https://git.openembedded.org/meta-openembedded/tree/meta-oe/recipes-support/htop/files/0001-Use-pkg-config.patch?id=110667ac3798b5b64552cb4b8dc706aad8fbcdfe

Using this patch, detection can be switched as appropriate.

[BenBE]

Something seems off with the Ubuntu build. Any ideas?

[fasterit]

Something seems off with the Ubuntu build. Any ideas?

I get the same on a local build with `--enable-static`` (on Debian bookworm) after your change:

...
checking for a way to check for ncurses... pkg-config (auto-detected)
checking for addnwstr in -lncursesw6... no
checking for addnwstr in -lncursesw... no
checking for addnwstr in -lncurses... no
configure: error: can not find required library libncursesw; you may want to use --disable-unicode

previously it compiles fine to a static executable and the configure output snippet is:

....
checking for waddwstr in -lncursesw6... no
checking for waddwstr in -lncursesw... yes
checking for ncursesw/curses.h... yes
checking for ncursesw/term.h... yes

[BenBE]

Does it build with ./configure --enable-static --with-check-ncurses=nc-config? Currently the patch changes the default when auto-detecting the setting.

[fasterit]

Does it build with ./configure --enable-static --with-check-ncurses=nc-config? Currently the patch changes the default when auto-detecting the setting.

Yes, it does.

...
checking for a way to check for ncurses... ncurses*-config helpers
checking for waddwstr in -lncursesw6... no
checking for waddwstr in -lncursesw... yes
checking for ncursesw/curses.h... yes
checking for ncursesw/term.h... yes
checking for library containing keypad... none required

[Explorer09]

The problem in my opinion is that it doesn't make sense to let user specify how to check ncurses. The user should only specify whether ncurses exists, and optionally how to link to it.
So the option should look like this: --with-ncurses=<libname> while <libname> could be ncursesw6, ncursesw5, ncurses6, ncurses, etc.
Perhaps we can also introduce two variables NCURSES_CFLAGS and NCURSES_LDFLAGS just to allow user to override the flags when the values retrieved from "*-config" has errors.

Now, when it comes to automatic detection of ncurses, I can suggest this order:

1. NCURSES_CFLAGS and NCURSES_LDFLAGS take highest priority if both are specified.
2. --with-ncurses=<libname> if user specifies it. We can retrieve NCURSES_CFLAGS and NCURSES_LDFLAGS with the specified library name. First through pkg-config, and then <libname>-config. The pkg-config is preferred as it's a more generic library information utility. If pkg-config is not available, look for <libname>-config instead (which is specific to ncurses information).
3. If user does not specify --with-ncurses, then we guess all possible names of ncurses installed in the user's system. First through pkg-config, and then <libname>-config.

[BenBE]

@Explorer09 Please see the linked patch from OpenEmbedded for context.

[Explorer09]

@BenBE I did read the linked patch, and thus I get the conclusion we are doing the wrong way.

The --with-check-ncurses variable should be internal to configure. These is no sense for user to specify that. Because either pkg-config works or it doesn't, and if user has to specify a awkward script name (say, ncursesfoo-config2) just to get the linker flags for ncurses, then their ncurses installation is broken. We don't need to find any script name other than <libname>-config because that's what the ncurses config information utility would be installed as. Thus, --with-ncurses=<libname> would be enough.

[BenBE]

Ideally the method with which you can detect ncurses should not matter. The special case with OpenEmbedded is that you are building a system (from scratch) with minimal tooling available in the build environment, thus it's totally reasonable for them to assume pkg-config to be available (minimal dev tooling), but not ncurses-config (which may need emulation to run). After all OpenEmbedded is usually used for cross-building, thus minimizing reliance on tooling used in build systems is absolutely justified.

What I'm more confused about though is that pkg-config seems to fail when finding libncurses6 in the static build case, but works for the normally linked one. Thus running configure with either methods (or a secret third option) should not make a difference for the build as long as proper settings are returned. And based on the OE patch running ncurses6-config or pkg-config ncurses6 should be equal. And THAT is the question that currently needs solving.

[Explorer09]

The problem in my opinion is that it doesn't make sense to let user specify how to check ncurses. The user should only specify whether ncurses exists, and optionally how to link to it. So the option should look like this: --with-ncurses=<libname> while <libname> could be ncursesw6, ncursesw5, ncurses6, ncurses, etc. Perhaps we can also introduce two variables NCURSES_CFLAGS and NCURSES_LDFLAGS just to allow user to override the flags when the values retrieved from "*-config" has errors.

I implemented the idea in #1512. Please take a look and make some comments.