meson.build: install our headers into a versioned subfolder

This makes it possible to have multiple (incompatible) versions
installed simultaneously.

Any incompatible version requires us bumping the major version, so our
headers are simply installed into the hardcoded libei-1.0 subdir.

This also changes the pkgconfig names to include the API version, so
it's now `pkgconfig --cflags libei-1.0`.

doc/api/mainpage.dox

@@ -71,8 +71,8 @@ Otherwise, the most rudimentary way to compile and link a program against
 libei or libeis is:
 
 @verbatim
-    gcc -o myprogram mylibeiclient.c `pkg-config --cflags --libs libei`
-    gcc -o myprogram myEISimplementation.c `pkg-config --cflags --libs libeis`
+    gcc -o myprogram mylibeiclient.c `pkg-config --cflags --libs libei-1.0`
+    gcc -o myprogram myEISimplementation.c `pkg-config --cflags --libs libeis-1.0`
 @endverbatim
 
 For further information on using pkgconfig see the pkg-config documentation.

meson.build

@@ -32,6 +32,11 @@ cflags =[
     '-Wswitch',
 ]
 
+# Our headers are in libei-1.0 until we hit 2.0 etc. libei's API is
+# backwards-compatible until the major version bump.
+libei_api_version = '1.0'
+libei_api_dir = 'libei-@0@'.format(libei_api_version)
+
 if cc.get_id() == 'clang'
     cflags += [
         # clang doesn't think just using _unref_ is a use of the variable

src/meson.build

@@ -68,16 +68,17 @@ lib_libei = library('ei',
     install: true
 )
 libei_headers = files('libei.h')
-install_headers(libei_headers)
+install_headers(libei_headers, subdir: libei_api_dir)
 
 dep_libei = declare_dependency(link_with: lib_libei,
                                 include_directories: [inc_src])
 meson.override_dependency('libei', dep_libei)
 
 pkgconfig.generate(lib_libei,
-    filebase: 'libei',
+    filebase: 'libei-@0@'.format(libei_api_version),
     name: 'libEI',
     description: 'Emulated Input client library',
+    subdirs: libei_api_dir,
     version: meson.project_version(),
     libraries: lib_libei,
 )
@@ -123,16 +124,17 @@ lib_libeis = library('eis',
     install: true
 )
 libeis_headers = files('libeis.h')
-install_headers(libeis_headers)
+install_headers(libeis_headers, subdir: libei_api_dir)
 
 dep_libeis = declare_dependency(link_with: lib_libeis,
                                 include_directories: [inc_src])
 meson.override_dependency('libeis', dep_libeis)
 
 pkgconfig.generate(lib_libeis,
-    filebase: 'libeis',
+    filebase: 'libeis-@0@'.format(libei_api_version),
     name: 'libEIS',
     description: 'Emulated Input server library',
+    subdirs: libei_api_dir,
     version: meson.project_version(),
     libraries: lib_libeis,
 )
@@ -150,16 +152,17 @@ if build_oeffis
         install: true
     )
     liboeffis_headers = files('liboeffis.h')
-    install_headers(liboeffis_headers)
+    install_headers(liboeffis_headers, subdir: libei_api_dir)
 
     dep_liboeffis = declare_dependency(link_with: lib_liboeffis,
                                        include_directories: [inc_src])
     meson.override_dependency('liboeffis', dep_liboeffis)
 
     pkgconfig.generate(lib_liboeffis,
-        filebase: 'liboeffis',
+        filebase: 'liboeffis-@0@'.format(libei_api_version),
         name: 'libOeffis',
         description: 'RemoteDesktop portal DBus helper library',
+        subdirs: libei_api_dir,
         version: meson.project_version(),
         libraries: lib_liboeffis,
     )