[scarthgap] chromium: Drop patch to decrease minimum Rust version (#858)

chromium: Drop patch to decrease minimum Rust version

Build and patch changes:
------------------------

Drop a patch to decrease the required version of Rust, and instead
depend on meta-lts-mixins to provide a more up-to-date version of Rust
than OE Core.

License changes:
----------------

None.

Test-built:
-----------

* chromium-ozone-wayland:
 - scarthgap, clang, MACHINE=raspberrypi4-64

Signed-off-by: Max Ihlenfeldt <max@igalia.com>

Author: MaxIhlenfeldt

meta-chromium/README.md

@@ -60,6 +60,16 @@ peculiarities:
 - Parts of the V8 (Chromium's JavaScript engine) build need to run binaries
   built for the target, for which we use QEMU.
 
+## Supported OE/Yocto releases
+
+We only support the master branch and the current LTS releases of OE/Yocto,
+using this repo's master branch for the former and separate branches for the
+latter.
+
+Recent non-LTS releases should still work with our master branch, and we'll
+create branches capturing the last buildable version once they stop working with
+the latest version.
+
 ## Build requirements
 
 This recipe requires clang, and GCC is not supported. Upstream Chromium has not
@@ -72,6 +82,21 @@ host. clang-native from the meta-clang layer is used to build those binaries.
 Additionally, make sure the machine being used to build Chromium is powerful
 enough: a x86-64 machine with at least 16GB RAM is recommended.
 
+### scarthgap-specific requirements
+
+The scarthgap OE/Yocto branch is an LTS release, which is often at odds with
+Chromium's release model because it often requires recent versions of certain
+recipes to build correctly.
+
+This is particularly a problem for the toolchain (i.e. LLVM/clang and Rust).
+Chromium needs a more recent version of Rust than OE Core provides for
+scarthgap, which is why we depend on meta-lts-mixins' `scarthgap/rust` branch.
+
+**Side note: For now, clang 18 provided by meta-clang is recent enough, but at
+some point during scarthgap's LTS lifetime Chromium won't be compilable with
+that version, and we'll have to create e.g. a scarthgap-clang20 branch for
+meta-clang and use that.**
+
 ## PACKAGECONFIG knobs
 
 * component-build: (off by default)

meta-chromium/conf/layer.conf

@@ -11,4 +11,4 @@ BBFILE_PRIORITY_chromium-browser-layer = "7"
 LAYERVERSION_chromium-browser-layer = "1"
 LAYERSERIES_COMPAT_chromium-browser-layer = "scarthgap styhead walnascar"
 
-LAYERDEPENDS_chromium-browser-layer = "clang-layer core openembedded-layer"
+LAYERDEPENDS_chromium-browser-layer = "clang-layer core openembedded-layer lts-rust-mixin"

meta-chromium/recipes-browser/chromium/chromium-gn.inc

@@ -27,7 +27,6 @@ SRC_URI += "\
     file://0010-Don-t-require-profiler_builtins.rlib.patch \
     file://0011-Disable-crabbyavif-to-fix-build-errors.patch \
     file://0012-Revert-Allow-and-use-std-hardware_destructive_interf.patch \
-    file://0013-Revert-Tell-rustc-that-we-will-always-be-providing-c.patch \
 "
 # ARM/AArch64-specific patches.
 SRC_URI:append:aarch64 = "${@bb.utils.contains('TUNE_FEATURES', 'crypto', '', ' file://arm/0001-Fix-AES-crypto-SIGILL-on-rpi4-64.patch', d)}"