[glib: 1/4] meson: simplify iconv lookups using Meson's builtin dependency lookup

[Philip Withnall <pwithnall src gnome org>]

commit 24ec80cfb4522d9819dbf5fd117665fef20b6418
Author: Eli Schwartz <eschwartz archlinux org>
Date:   Tue Jun 7 16:14:04 2022 -0400

    meson: simplify iconv lookups using Meson's builtin dependency lookup
    
    iconv is complicated to look up. That complexity now resides in
    Meson, since 0.60.0, via a `dependency('iconv')` lookup, so use that
    instead.
    
    No effort is made to support the old option for which type of iconv to
    use. It was a false choice, because if only one was available, then
    that's the only one you can use, and if both are available, the external
    iconv shadows the builtin one and renders the builtin one unusable,
    so there is still only one you can use.
    
    This meant that when configuring glib with -Diconv=libc on systems that
    had an external iconv, the configure check would detect a valid libc
    iconv, try to use it, and then fail during the build because iconv.h
    belongs to the external iconv and generates machine code using the
    external iconv ABI, but fails to link to the iconv `find_library()`.
    Meson handles this transparently.

 .gitlab-ci.yml                   |  5 ++---
 docs/reference/glib/building.xml | 18 +++++++-----------
 meson.build                      | 20 ++------------------
 meson_options.txt                |  4 ++--
 4 files changed, 13 insertions(+), 34 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 6673c237b6..518b53e0f1 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -386,11 +386,10 @@ freebsd-12-x86_64:
     - bash .gitlab-ci/show-execution-environment.sh
   script:
     # We cannot use -Wl,--no-undefined because GLib uses 'environ' variable.
-    # FreeBSD iconv doesn't handle transliteration, so we use (external) GNU libiconv here.
     # FreeBSD supports xattr, but its API is different from Linux xattr.
     # FIXME: extattr(2) support: https://gitlab.gnome.org/GNOME/glib/issues/1404
     # localstatedir is needed for access to /var/lib/dbus/machine-id
-    - meson ${MESON_COMMON_OPTIONS} --localstatedir=/var -Db_lundef=false -Diconv=external -Dxattr=false 
_build
+    - meson ${MESON_COMMON_OPTIONS} --localstatedir=/var -Db_lundef=false -Dxattr=false _build
     - ninja -C _build
     - bash -x ./.gitlab-ci/run-tests.sh
   artifacts:
@@ -417,7 +416,7 @@ freebsd-13-x86_64:
   before_script:
     - bash .gitlab-ci/show-execution-environment.sh
   script:
-    - meson ${MESON_COMMON_OPTIONS} --localstatedir=/var -Db_lundef=false -Diconv=external -Dxattr=false 
_build
+    - meson ${MESON_COMMON_OPTIONS} --localstatedir=/var -Db_lundef=false -Dxattr=false _build
     - ninja -C _build
     - bash -x ./.gitlab-ci/run-tests.sh
   artifacts:
diff --git a/docs/reference/glib/building.xml b/docs/reference/glib/building.xml
index d165c5c233..62f1c3bc23 100644
--- a/docs/reference/glib/building.xml
+++ b/docs/reference/glib/building.xml
@@ -29,7 +29,7 @@
 
       On FreeBSD:
       <literallayout>
-        <userinput>env CPPFLAGS="-I/usr/local/include" LDFLAGS="-L/usr/local/lib -Wl,--disable-new-dtags" 
meson -Dxattr=false -Dinstalled_tests=true -Diconv=external -Db_lundef=false _build</userinput>
+        <userinput>env CPPFLAGS="-I/usr/local/include" LDFLAGS="-L/usr/local/lib -Wl,--disable-new-dtags" 
meson -Dxattr=false -Dinstalled_tests=true -Db_lundef=false _build</userinput>
         <userinput>ninja -C _build</userinput>
       </literallayout>
     </para>
@@ -98,16 +98,12 @@
         </para>
         <para>
           If your system has an <function>iconv()</function> implementation but
-          you want to use libiconv instead, you can pass the
-          <option>-Diconv=gnu</option> option to <command>meson</command>. This
-          forces libiconv to be used.
-        </para>
-        <para>
-          Note that if you have libiconv installed in your default include
-          search path (for instance, in <filename>/usr/local/</filename>), but
-          don't enable it, you will get an error while compiling GLib because
-          the <filename>iconv.h</filename> that libiconv installs hides the
-          system iconv.
+          you want to use libiconv instead, make sure it is installed to the
+          default compiler header/library search path (for instance, in
+          <filename>/usr/local/</filename>). The <filename>iconv.h</filename>
+          that libiconv installs hides the system iconv. Meson then detects
+          this, recognizes that the system iconv is unusable and the external
+          one is mandatory, and automatically forces it to be used.
         </para>
         <para>
           If you are using the native iconv implementation on Solaris
diff --git a/meson.build b/meson.build
index ee0a6234c4..424aede80c 100644
--- a/meson.build
+++ b/meson.build
@@ -1976,28 +1976,12 @@ glibconfig_conf.set10('G_HAVE_GROWING_STACK', growing_stack)
 # We should never use the MinGW C library's iconv because it may not be
 # available in the actual runtime environment. On Windows, we always use
 # the built-in implementation
-iconv_opt = get_option('iconv')
 if host_system == 'windows'
-  libiconv = []
   # We have a #include "win_iconv.c" in gconvert.c on Windows, so we don't need
   # any external library for it
-  if iconv_opt != 'auto'
-    warning('-Diconv was set to @0@, which was ignored')
-  endif
+  libiconv = []
 else
-  found_iconv = false
-  if ['auto', 'libc'].contains(iconv_opt) and cc.has_function('iconv_open')
-    libiconv = []
-    found_iconv = true
-  endif
-  if not found_iconv and ['auto', 'external'].contains(iconv_opt) and cc.has_header_symbol('iconv.h', 
'iconv_open')
-    libiconv = [cc.find_library('iconv')]
-    found_iconv = true
-  endif
-
-  if not found_iconv
-    error('iconv implementation "@0@" not found'.format(iconv_opt))
-  endif
+  libiconv = dependency('iconv')
 endif
 
 pcre = dependency('libpcre', version: '>= 8.31', required : false) # Should check for Unicode support, too. 
FIXME
diff --git a/meson_options.txt b/meson_options.txt
index d1859e939d..a52eed9d26 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -7,7 +7,7 @@ option('iconv',
        type : 'combo',
        choices : ['auto', 'libc', 'external'],
        value : 'auto',
-       description : 'iconv implementation to use (\'libc\' = \'Part of the C library\'; \'external\' = 
\'External libiconv\'; \'auto\' = \'Auto-detect which iconv is available\')')
+       deprecated: true,)
 
 option('charsetalias_dir',
        type : 'string',
@@ -116,4 +116,4 @@ option('glib_checks',
 option('libelf',
        type : 'feature',
        value : 'auto',
-       description : 'Enable support for listing and extracting from ELF resource files with gresource tool')
\ No newline at end of file
+       description : 'Enable support for listing and extracting from ELF resource files with gresource tool')