Allow using msys2 instead of cygwin

.github/workflows/workflow.yml

@@ -53,6 +53,8 @@ jobs:
           - windows-latest
         ocaml-compiler:
           - "5.2"
+        windows-environment:
+          - ""
         allow-prerelease-opam:
           - false
         include:
@@ -62,6 +64,10 @@ jobs:
           - os: ubuntu-latest
             ocaml-compiler: "5.2"
             allow-prerelease-opam: true
+          - os: windows-latest
+            ocaml-compiler: "5.2"
+            windows-environment: msys2
+            allow-prerelease-opam: false
 
     runs-on: ${{ matrix.os }}
 
@@ -74,5 +80,6 @@ jobs:
         with:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
           allow-prerelease-opam: ${{ matrix.allow-prerelease-opam }}
+          windows-environment: ${{ matrix.windows-environment }}
 
       - run: opam install ssl

action.yml

@@ -37,6 +37,9 @@ inputs:
     description: The prefix of the cache keys.
     required: false
     default: v1
+  windows-environment:
+    description: Whether to use `cygwin` (default) or `msys2` for windows installs.
+    required: false
   github-token:
     description: DO NOT SET THIS.
     required: false

packages/setup-ocaml/src/cache.ts

@@ -18,6 +18,7 @@ import {
   OPAM_ROOT,
   PLATFORM,
   RESOLVED_COMPILER,
+  WINDOWS_ENVIRONMENT,
 } from "./constants.js";
 import { retrieveLatestOpamRelease } from "./opam.js";
 import { retrieveCygwinVersion } from "./windows.js";
@@ -50,6 +51,7 @@ async function composeOpamCacheKeys() {
   const ocamlCompiler = await RESOLVED_COMPILER;
   const repositoryUrls = OPAM_REPOSITORIES.map(([_, value]) => value).join();
   const osInfo = await system.osInfo();
+  const msys2 = WINDOWS_ENVIRONMENT === "msys2" ? "msys2" : undefined;
   const plainKey = [
     PLATFORM,
     osInfo.release,
@@ -58,7 +60,9 @@ async function composeOpamCacheKeys() {
     ocamlCompiler,
     repositoryUrls,
     sandbox,
-  ].join();
+  ]
+    .concat(msys2 ?? [])
+    .join();
   const hash = crypto.createHash("sha256").update(plainKey).digest("hex");
   const key = `${CACHE_PREFIX}-setup-ocaml-opam-${hash}`;
   const restoreKeys = [key];
@@ -203,7 +207,7 @@ async function restoreOpamCache() {
 export async function restoreOpamCaches() {
   return await core.group("Retrieve the opam cache", async () => {
     const [opamCacheHit, cygwinCacheHit] = await Promise.all(
-      PLATFORM === "windows"
+      PLATFORM === "windows" && WINDOWS_ENVIRONMENT === "cygwin"
         ? [restoreOpamCache(), restoreCygwinCache()]
         : [restoreOpamCache()],
     );

packages/setup-ocaml/src/constants.ts

@@ -86,6 +86,23 @@ export const ALLOW_PRERELEASE_OPAM = core.getBooleanInput(
   },
 );
 
+export const WINDOWS_ENVIRONMENT: "cygwin" | "msys2" = (() => {
+  const input = core.getInput("windows-environment");
+
+  if (!(PLATFORM === "windows" || input === "")) {
+    core.error("windows-environment is only supported on windows");
+  }
+
+  if (input === "msys2" || input === "cygwin") {
+    return input;
+  }
+
+  if (input !== "") {
+    core.error("unrecognized value for windows-environment");
+  }
+  return "cygwin";
+})();
+
 export const CACHE_PREFIX = core.getInput("cache-prefix", {
   required: false,
   trimWhitespace: true,

packages/setup-ocaml/src/installer.ts

@@ -10,6 +10,7 @@ import {
   saveOpamCache,
 } from "./cache.js";
 import {
+  CYGWIN_ROOT,
   CYGWIN_ROOT_BIN,
   DUNE_CACHE,
   DUNE_CACHE_ROOT,
@@ -18,6 +19,7 @@ import {
   OPAM_ROOT,
   PLATFORM,
   RESOLVED_COMPILER,
+  WINDOWS_ENVIRONMENT,
 } from "./constants.js";
 import { installDune } from "./dune.js";
 import {
@@ -29,7 +31,7 @@ import {
   update,
 } from "./opam.js";
 import { retrieveOpamLocalPackages } from "./packages.js";
-import { setupCygwin } from "./windows.js";
+import { prepareMsys2, setupCygwin } from "./windows.js";
 
 export async function installer() {
   if (core.isDebug()) {
@@ -64,13 +66,24 @@ export async function installer() {
   }
   const { opamCacheHit, cygwinCacheHit } = await restoreOpamCaches();
   if (PLATFORM === "windows") {
-    await setupCygwin();
-    if (!cygwinCacheHit) {
-      await saveCygwinCache();
+    switch (WINDOWS_ENVIRONMENT) {
+      case "msys2": {
+        const msys2Root = await prepareMsys2();
+        await setupOpam(msys2Root);
+        break;
+      }
+      case "cygwin":
+        await setupCygwin();
+        if (!cygwinCacheHit) {
+          await saveCygwinCache();
+        }
+        core.addPath(CYGWIN_ROOT_BIN);
+        await setupOpam(CYGWIN_ROOT);
+        break;
     }
-    core.addPath(CYGWIN_ROOT_BIN);
+  } else {
+    await setupOpam();
   }
-  await setupOpam();
   if (!opamCacheHit) {
     await repositoryRemoveAll();
     await repositoryAddAll(OPAM_REPOSITORIES);