[Buildroot] [PATCH 3/3 v4] package/qt5/qt5webengine: fix build dependencies for autodetected packages

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

On Wed, 16 Sep 2020 23:11:34 +0200
"Yann E. MORIN" <yann.morin.1998@free.fr> wrote:

> +ifeq ($(BR2_PACKAGE_JSONCPP),y)
> +QT5WEBENGINE_DEPENDENCIES += jsoncpp
> +endif
> +
> +ifeq ($(BR2_PACKAGE_LCMS2),y)
> +QT5WEBENGINE_DEPENDENCIES += lcms2
> +endif
> +
> +ifeq ($(BR2_PACKAGE_LIBEVENT),y)
> +QT5WEBENGINE_DEPENDENCIES += libevent
> +endif
> +
> +ifeq ($(BR2_PACKAGE_LIBXML2),y)
> +QT5WEBENGINE_DEPENDENCIES += libxml2
> +endif
> +
> +ifeq ($(BR2_PACKAGE_LIBXSLT),y)
> +QT5WEBENGINE_DEPENDENCIES += libxslt
> +endif
> +
> +ifeq ($(BR2_PACKAGE_PROTOBUF),y)
> +QT5WEBENGINE_DEPENDENCIES += protobuf
> +endif
> +
> +ifeq ($(BR2_PACKAGE_SNAPPY),y)
> +QT5WEBENGINE_DEPENDENCIES += snappy
> +endif

I am not 100% sure but I believe those dependencies do have options,
much like the -webengine-ffmpeg option that PATCH 1/3 is using. If you
look at ./src/core/configure.json in the qt5webengine sources, you can
see:

    "commandline": {
        "options": {
            "webengine-alsa": "boolean",
            "webengine-embedded-build": "boolean",
            "webengine-full-debug-info": "boolean",
            "webengine-icu": { "type": "enum", "name": "webengine-system-icu", "values": { "system": "yes", "qt": "no" } },
            "webengine-ffmpeg": { "type": "enum", "name": "webengine-system-ffmpeg", "values": { "system": "yes", "qt": "no" } },
            "webengine-opus": { "type": "enum", "name": "webengine-system-opus", "values": { "system": "yes", "qt": "no" } },
            "webengine-webp": { "type": "enum", "name": "webengine-system-libwebp", "values": { "system": "yes", "qt": "no" } },
            "webengine-pepper-plugins": "boolean",
            "webengine-printing-and-pdf": "boolean",
            "webengine-proprietary-codecs": "boolean",
            "webengine-pulseaudio": "boolean",
            "webengine-spellchecker": "boolean",
            "webengine-native-spellchecker": "boolean",
            "webengine-extensions": "boolean",
            "webengine-webrtc": "boolean",
            "webengine-geolocation": "boolean",
            "webengine-webchannel": "boolean",
            "webengine-kerberos": "boolean",
            "alsa": { "type": "boolean", "name": "webengine-alsa" },
            "pulseaudio": { "type": "boolean", "name": "webengine-pulseaudio" },
            "ffmpeg": { "type": "enum", "name": "webengine-system-ffmpeg", "values": { "system": "yes", "qt": "no" } },
            "opus": { "type": "enum", "name": "webengine-system-opus", "values": { "system": "yes", "qt": "no" } },
            "webp": { "type": "enum", "name": "webengine-system-libwebp", "values": { "system": "yes", "qt": "no" } },
            "pepper-plugins": { "type": "boolean", "name": "webengine-pepper-plugins" },
            "printing-and-pdf": { "type": "boolean", "name": "webengine-printing-and-pdf" },
            "proprietary-codecs": { "type": "boolean", "name": "webengine-proprietary-codecs" },
            "spellchecker": { "type": "boolean", "name": "webengine-spellchecker" },
            "extensions": { "type": "boolean", "name": "webengine-extensions" },
            "webrtc": { "type": "boolean", "name": "webengine-webrtc" }
        }
    },

So it seems like if we have a -webengine-ffmpeg option, then we should
also have many other options to enable (and perhaps disable ?) other
optional features.

However, I'm not sure to understand the difference between the
"webengine-<something>" option and the corresponding "<something>"
option.

Also, it seems like some options such as webengine-ffmpeg or
webengine-icu can take multiple values: they are enums and not
booleans. should we use -webengine-ffmpeg=system for example ? Ditto
for the other dependencies;

For the record, the qt5webengine source code bundles chromium in
./src/3rdparty/, which itself bundles a bunch of things including
ffmpeg in ./src/3rdparty/chromium/third_party/ffmpeg/ (do you like when
a 3rdparty folder includes another third_party folder ?).

Obviously, in the context of Buildroot, we'd prefer to use as few
bundled libraries as possible, and use as much as possible system
libraries.

How is the configure.json above being parsed and used ?

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com