add spngsave to meson build

libvips/foreign/meson.build

@@ -43,6 +43,7 @@ foreign_sources = files(
     'rawload.c',
     'rawsave.c',
     'spngload.c',
+    'spngsave.c',
     'svgload.c',
     'tiff2vips.c',
     'tiff.c',

meson.build

@@ -249,18 +249,22 @@ if libjpeg_dep.found()
 endif
 
 # Look for libspng first
-# 0.6.1 uses "libspng.pc", git master libspng uses "spng.pc"
-# We can simplify this when requiring meson>=0.60.0
-spng_dep = dependency('libspng', version: '>=0.6', required: false)
+# - it's sometimes called "spng.pc", sometimes "libspng.pc", we must search for
+#   both
+# - we need 0.7+ for PNG write support
+# - simplify this when requiring meson>=0.60.0
+spng_dep = dependency('libspng', version: '>=0.7', required: get_option('spng'))
 if not spng_dep.found()
-    spng_dep = dependency('spng', version: '>=0.6', required: get_option('spng'))
+    spng_dep = dependency('spng', version: '>=0.7', required: get_option('spng'))
 endif
 if not get_option('spng').disabled() and spng_dep.found()
     libvips_deps += spng_dep
     cfg_var.set('HAVE_SPNG', '1')
 endif
 
-# we can have both PNG and SPNG enabled, with SPNG for read and PNG for write
+# only if libspng not found
+png_dep = disabler()
+if not spng_dep.found()
     png_dep = dependency('libpng', version: '>=1.2.9', required: get_option('png'))
     if png_dep.found()
         libvips_deps += png_dep
@@ -269,11 +273,12 @@ if png_dep.found()
             cfg_var.set('HAVE_PNG_SET_CHUNK_MALLOC_MAX', '1')
         endif
     endif
+endif
 
 
 # libwebp ... target 0.6+ to reduce complication
 # webp has the stuff for handling metadata in two separate libraries -- we
-# insit on having all of them
+# insist on having both of them
 libwebp_dep = dependency('libwebp', version: '>=0.6', required: get_option('png'))
 if libwebp_dep.found()
     libvips_deps += libwebp_dep