Work on proper build integration

Install hb-cairo.h and define HB_HAS_CAIRO.

docs/harfbuzz-sections.txt

@@ -170,6 +170,7 @@ HB_HAS_CORETEXT
 HB_HAS_FREETYPE
 HB_HAS_GLIB
 HB_HAS_GRAPHITE
+HB_HAS_CAIRO
 <SUBSECTION Private>
 HB_BEGIN_DECLS
 HB_END_DECLS

src/hb-features.h.in

@@ -84,6 +84,13 @@ HB_BEGIN_DECLS
  */
 #mesondefine HB_HAS_ICU
 
+/**
+ * HB_HAS_CAIRO:
+ *
+ * Defined if Harfbuzz has been built with cairo support.
+ */
+#mesondefine HB_HAS_CAIRO
+
 
 HB_END_DECLS
 

src/meson.build

@@ -483,6 +483,10 @@ if have_icu and have_icu_builtin
   hb_features.set('HB_HAS_ICU', 1)
 endif
 
+if conf.get('HAVE_CAIRO', 0) == 1
+  hb_features.set('HB_HAS_CAIRO', 1)
+endif
+
 hb_features_h = configure_file(input: 'hb-features.h.in',
                                output: 'hb-features.h',
                                configuration: hb_features,
@@ -577,24 +581,39 @@ libharfbuzz_subset_dep = declare_dependency(
   dependencies: [m_dep])
 meson.override_dependency('harfbuzz-subset', libharfbuzz_subset_dep)
 
-hb_cairo_sources = [
-  'hb-cairo.cc',
-  'hb-cairo-utils.cc'
-]
+libharfbuzz_cairo_dep = null_dep
+if conf.get('HAVE_CAIRO', 0) == 1
+  hb_cairo_sources = [
+    'hb-cairo.cc',
+    'hb-cairo-utils.cc'
+  ]
 
-cairo_dep = dependency('cairo')
+  hb_cairo_headers = [
+    'hb-cairo.h',
+  ]
 
-libharfbuzz_cairo = library('harfbuzz-cairo', hb_cairo_sources,
-  include_directories: incconfig,
-  dependencies: [m_dep, cairo_dep],
-  link_with: [libharfbuzz],
-  cpp_args: cpp_args + extra_hb_cpp_args,
-  soversion: hb_so_version,
-  version: version,
-  install: true,
-  darwin_versions: darwin_versions,
-  link_language: 'c',
-)
+  cairo_dep = dependency('cairo')
+
+  libharfbuzz_cairo = library('harfbuzz-cairo', hb_cairo_sources,
+    include_directories: incconfig,
+    dependencies: [m_dep, cairo_dep],
+    link_with: [libharfbuzz],
+     cpp_args: cpp_args + extra_hb_cpp_args,
+    soversion: hb_so_version,
+    version: version,
+    install: true,
+    darwin_versions: darwin_versions,
+    link_language: 'c',
+  )
+
+  install_headers(hb_cairo_headers, subdir: meson.project_name())
+
+  libharfbuzz_cairo_dep = declare_dependency(
+    link_with: libharfbuzz_cairo,
+    include_directories: incsrc,
+    dependencies: [m_dep, cairo_dep])
+  meson.override_dependency('harfbuzz-cairo', libharfbuzz_cairo_dep)
+endif
 
 if get_option('tests').enabled()
   # TODO: MSVC gives the following,