add compiler auto to use dmd or ldc depending on architecture

README.md

@@ -10,7 +10,7 @@ steps:
   - uses: actions/checkout@v2
   - uses: dlang-community/setup-dlang@v1
     with:
-      compiler: dmd-latest
+      compiler: auto # dmd-latest, ldc-latest, ...
   - name: Run tests
     run: dub test
 ```
@@ -51,6 +51,8 @@ All DMD versions of releases and pre-releases on https://downloads.dlang.org/rel
 
 Additionally instead of a version for both DMD and LDC you can specify `-latest` to get the latest stable release of the compiler, use `-beta` to get the latest pre-release of the compiler and also use `-master` to get the newest nightly builds.
 
+When no compiler is specified, or when it is set to `auto`, `dmd-latest` will be picked, unless it's running on a non-x86 platform (e.g. ARM), then `ldc-latest` will be picked.
+
 Valid version examples are:
 - `dmd-latest`
 - `ldc-latest`

action.yml

@@ -4,7 +4,7 @@ author: "Mihails Strasuns"
 inputs:
   compiler:
     description: "Compiler version string, for example 'dmd-latest' or 'ldc-1.20.1'"
-    default: "dmd-latest"
+    default: "auto"
   dub:
     description: "DUB version string, for example 'latest' or '1.29.0'"
     required: false

src/main.ts

@@ -12,7 +12,8 @@ async function run() {
         if (process.arch != "x64") {
             default_compiler = "ldc-latest";
         }
-        const input = core.getInput('compiler') || default_compiler;
+        let input = core.getInput('compiler') || 'auto';
+        if (input === 'auto') input = default_compiler;
         if (process.arch != "x64" && input.startsWith("dmd"))
             throw new Error("The dmd compiler is not supported for non-x64 architecture");