native xmake toolchain definition for UE-clang (#805)

This change is meant to provide a smoother experience when working on Linux. After this change, the toolchain setup process is now simply

```bash
$ scripts/ue_build_linux/get_ue_toolchain.sh 
```

and then at config time the toolchain is automatically detected if you downloaded it to the default location or have the `UE_TOOLCHAIN_DIR` environment variable set

```bash
xmake config --mode=debug
```

Compared to the old script-based approach this configures the toolchain more precisely, avoiding leakage into unrelated build processes such as when a package manager decides to build something like Ninja locally etc.

6 files changed, 32 insertions, 59 deletions

diff --git a/scripts/bundle.lua b/scripts/bundle.lua
index 07e120d04..b2a5e1e08 100644
--- a/scripts/bundle.lua
+++ b/scripts/bundle.lua
@@ -17,7 +17,15 @@ end
 
 --------------------------------------------------------------------------------
 local function _build(arch, debug, config_args)
+    import("core.project.config")
+    config.load()
+
     variant = debug and "debug" or "release"
+
+    -- Preserve toolchain/sdk from current config so --clean doesn't lose them
+    local toolchain_arg = config.get("toolchain") and ("--toolchain=" .. config.get("toolchain")) or nil
+    local sdk_arg = config.get("sdk") and ("--sdk=" .. config.get("sdk")) or nil
+
     local ret = _exec(
         "xmake",
         "config",
@@ -26,6 +34,8 @@ local function _build(arch, debug, config_args)
         "--mode="..variant,
         "--arch="..arch,
         "--zensentry=yes",
+        toolchain_arg,
+        sdk_arg,
         config_args)
     if ret > 0 then
         raise("Failed to configure xmake")
diff --git a/scripts/ue_build_linux/README.md b/scripts/ue_build_linux/README.md
index e93a234ae..afafcbe24 100755
--- a/scripts/ue_build_linux/README.md
+++ b/scripts/ue_build_linux/README.md
@@ -2,38 +2,38 @@
 

 This folder contains scripts to build Zen using the UE Linux toolchain. This

 can be used to output binaries that meet the VFX Reference Platform versions.

-It works by using the `--sysroot=` option to redirect compilers and linkers to

-find headers and libraries. There are a few components involved;

 

-1) get_ue_toolchain.sh <toolchain_dir>

+## Setup

+

+Download the toolchain using `get_ue_toolchain.sh`:

 

 ```

-$ scripts/ue_build_linux/get_ue_toolchain.sh ./.tmp-ue-toolchain

+$ scripts/ue_build_linux/get_ue_toolchain.sh

 ```

 

-This will download the required components from cdn.unrealengine.com and

-structure them in such a way that they can be used by both vcpkg and xmake

-when building Zen.

+By default this downloads to `~/.ue-toolchain`. A custom path can be given as

+the first argument, or via the `UE_TOOLCHAIN_DIR` environment variable.

 

-2) ue_build.sh <toolchain_dir> <prog> [args...] 

+This will download the required components from cdn.unrealengine.com and

+structure them in such a way that they can be used by xmake when building Zen.

 

-Given the toolchain location downloaded in step (1) and the `VCPKG_ROOT`

-environment variable is properly configured, this script sets up a suitable

-environment and execs the "prog [args...]".

+## Building

 

-It is expected that this is used to invoke xmake to build Zen;

+xmake automatically detects the toolchain at `~/.ue-toolchain`, so no extra

+flags are needed:

 

 ```

-$ scripts/ue_build_linux/ue_build.sh .tmp-ue-toolchain xmake config --mode=debug

-$ scripts/ue_build_linux/ue_build.sh .tmp-ue-toolchain xmake build

+$ xmake config -y -m debug

+$ xmake build -y

 ```

 

-It is possible that `--toolchain=clang` may be required as a configuration

-option. The `ue_build.sh` script can also be sourced into the current shell,

-although it is worth noting that this has never been tried.

+To build a release bundle:

 

-3) `scripts/ue_build_linux/clang` / `scripts/ue_build_linux/clang++`

+```

+$ xmake config -y -m release

+$ xmake bundle -y

+```

 

-These acts as shims to the binaries in `toolchain_dir`, adding in the required

-command line arguments to use the correct headers and libraries.

-The `ue_build.sh` script adjusts `$PATH` appropriately.

+The toolchain can also be selected explicitly with `--toolchain=ue-clang`, and

+the SDK location can be overridden with `--sdk=<path>` (must be absolute) or

+the `UE_TOOLCHAIN_DIR` environment variable.

diff --git a/scripts/ue_build_linux/clang b/scripts/ue_build_linux/clang
deleted file mode 100755
index 9666ba4ba..000000000
--- a/scripts/ue_build_linux/clang
+++ /dev/null
@@ -1,2 +0,0 @@
-#!/bin/sh
-exec $UE_TOOLCHAIN_DIR/bin/clang --sysroot=$UE_TOOLCHAIN_DIR $CFLAGS "$@"
diff --git a/scripts/ue_build_linux/clang++ b/scripts/ue_build_linux/clang++
deleted file mode 100755
index be106ae87..000000000
--- a/scripts/ue_build_linux/clang++
+++ /dev/null
@@ -1,2 +0,0 @@
-#!/bin/sh
-exec $UE_TOOLCHAIN_DIR/bin/clang++ --sysroot=$UE_TOOLCHAIN_DIR -stdlib=libc++ $CXXFLAGS "$@"
diff --git a/scripts/ue_build_linux/get_ue_toolchain.sh b/scripts/ue_build_linux/get_ue_toolchain.sh
index c2538b09a..0afd40fe3 100755
--- a/scripts/ue_build_linux/get_ue_toolchain.sh
+++ b/scripts/ue_build_linux/get_ue_toolchain.sh
@@ -5,7 +5,7 @@ ZEN_ROOT=$(realpath $SCRIPT_DIR/../..)
 
 die() { echo "ERROR: $1"; exit; }
 
-toolchain_dir="${1:-${ZEN_ROOT}/.tmp-ue-toolchain}"
+toolchain_dir="${1:-${UE_TOOLCHAIN_DIR:-${HOME}/.ue-toolchain}}"
 
 if [[ $toolchain_dir == "--help" ]]; then
 	echo "usage: $(basename ${BASH_SOURCE[0]}) <output_dir>"
diff --git a/scripts/ue_build_linux/ue_build.sh b/scripts/ue_build_linux/ue_build.sh
deleted file mode 100755
index 690f9f661..000000000
--- a/scripts/ue_build_linux/ue_build.sh
+++ /dev/null
@@ -1,33 +0,0 @@
-#!/bin/bash
-
-SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
-ZEN_ROOT=$(realpath $SCRIPT_DIR/../..)
-
-die() { echo ERROR: $1; exit 1; }
-
-if [[ $1 == "--help" ]]; then
-	echo "usage: $0 <ue_toolchain_dir> (defaults to ${ZEN_ROOT}/.tmp-ue-toolchain)"
-	exit
-fi
-
-toolchain_dir="${1:-${ZEN_ROOT}/.tmp-ue-toolchain}"
-
-# Validate input
-
-if ! [ -d $toolchain_dir ]; then
-	die "$1 is not a directory"
-fi
-
-if ! [ -e $toolchain_dir/bin/clang++ ]; then
-	die "$1/bin/clang++ does not exist"
-fi
-
-export UE_TOOLCHAIN_DIR=$(realpath $toolchain_dir)
-export CC="clang"
-export CXX="clang++"
-export LD="clang++"
-
-export PATH="$(realpath $(dirname ${BASH_SOURCE[0]})):$PATH"
-
-shift
-exec "$@"