From bc9484d78f47e532752595954ccb13c78040d725 Mon Sep 17 00:00:00 2001
From: Sergey Fedorov <barracuda@macos-powerpc.org>
Date: Fri, 31 Jul 2026 15:13:35 +0000
Subject: [PATCH] meson: add a giflib option to select the giflib installation

giflib ships no pkg-config file, so find_library() picks whatever
gif library sits in the default search path. That breaks on systems
with several giflib versions installed: MacPorts keeps giflib 4 at
the prefix root (/opt/local/lib) and newer versions under
/opt/local/libexec/giflib5 and /opt/local/libexec/giflib6, so the
build silently picked giflib 4 while the decoder uses the giflib 5
API.

Add a 'giflib' string option naming the installation prefix to use
(-Dgiflib=/opt/local/libexec/giflib5), wiring its include and lib
directories into the dependency. Also verify that whichever giflib
was found actually provides the version 5 API, by probing for
DGifSavedExtensionToGCB: with -Dgif=enabled an unsuitable giflib is
now a configuration error instead of a compile failure, and with
the default auto it cleanly disables GIF support.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G6m1eevhAns3j85HMZYKna
---
 meson.build   | 21 +++++++++++++++++++++
 meson.options | 10 ++++++++++
 2 files changed, 31 insertions(+)

diff --git a/meson.build b/meson.build
index 6510d39..ff0f7da 100644
--- meson.build
+++ meson.build
@@ -105,8 +105,14 @@ webp_demux = dependency('libwebpdemux', required: get_option('webp'))
 # hack to build "pkgconfigless" gif in FreeBSD
 cc = meson.get_compiler('c')
 gif_opt = get_option('gif')
+gif_prefix = get_option('giflib')
+gif_args = []
 if gif_opt.disabled()
     gif = cc.find_library('gif', required: gif_opt)
+elif gif_prefix != ''
+    # Explicitly selected giflib installation.
+    gif_args = ['-I' + gif_prefix / 'include']
+    gif = cc.find_library('gif', dirs: gif_prefix / 'lib', required: gif_opt)
 else
     gif = cc.find_library('gif', required: false)
     if not gif.found() and gif_opt.allowed()
@@ -117,6 +123,21 @@ else
         )
     endif
 endif
+# The decoder uses the giflib 5 API; reject older versions instead of
+# failing the build (DGifSavedExtensionToGCB appeared in giflib 5).
+if gif.found()
+    if not cc.has_header_symbol('gif_lib.h', 'DGifSavedExtensionToGCB',
+                                args: gif_args)
+        if gif_opt.enabled()
+            error('giflib >= 5 is required; ' +
+                  'use -Dgiflib=<prefix> to select a suitable installation')
+        endif
+        message('giflib found, but older than version 5; GIF support disabled')
+        gif = cc.find_library('gif', dirs: '/var/empty', required: false)
+    elif gif_args.length() > 0
+        gif = declare_dependency(compile_args: gif_args, dependencies: gif)
+    endif
+endif
 
 # optional dependencies: other features
 exiv = dependency('exiv2', required: get_option('exif'))
diff --git a/meson.options b/meson.options
index 36c60b4..a3dc409 100644
--- meson.options
+++ meson.options
@@ -11,6 +11,16 @@ option(
     value: 'auto',
     description: 'Enable GIF format support',
 )
+option(
+    'giflib',
+    type: 'string',
+    value: '',
+    description: 'Prefix of the giflib installation to use. giflib ships ' +
+                 'no pkg-config file, so it cannot be discovered reliably ' +
+                 'when several versions are installed (e.g. MacPorts keeps ' +
+                 'giflib 4 at the prefix root and newer ones under ' +
+                 'libexec/giflib5). Example: /opt/local/libexec/giflib5',
+)
 option(
     'heif',
     type: 'feature',