Better handling of platforms when downloading

Check whether platform is supported before moving on

Add some tests to ensure it's the case. Also that we support
all said platform (file can actually be downloaded). This test suite
is slow, but I think it's worth it

Note: in future releases, windows support will need to be reworked.
in some instances, the `exe` is gone and replaced with a zip that'll
likely need to unpack

src/coursier/coursier.ts

@@ -6,7 +6,11 @@ export function getCoursierExecutable(extensionPath: string): Promise<string> {
     if (paths.length > 0) {
       return paths[0];
     } else {
-      return downloadCoursierIfRequired(extensionPath, "v2.0.6");
+      return downloadCoursierIfRequired(
+        extensionPath,
+        process.platform,
+        "v2.0.13"
+      );
     }
   });
 }

src/coursier/download-coursier.ts

@@ -6,6 +6,7 @@ import { access, mkdir } from "fs/promises";
 
 export function downloadCoursierIfRequired(
   extensionPath: string,
+  platform: string,
   versionPath: string
 ): Promise<string> {
   function binPath(filename: string) {
@@ -20,25 +21,32 @@ export function downloadCoursierIfRequired(
     });
   }
 
-  const urls = {
-    darwin: `https://github.com/coursier/coursier/releases/download/${versionPath}/cs-x86_64-apple-darwin`,
-    linux: `https://github.com/coursier/coursier/releases/download/${versionPath}/cs-x86_64-pc-linux`,
-    win32: `https://github.com/coursier/coursier/releases/download/${versionPath}/cs-x86_64-pc-win32.exe`,
-  };
-  const targets = {
-    darwin: binPath("coursier"),
-    linux: binPath("coursier"),
-    win32: binPath("coursier.exe"),
+  const supportedTargets = {
+    darwin: {
+      url: `https://github.com/coursier/coursier/releases/download/${versionPath}/cs-x86_64-apple-darwin`,
+      bin: binPath("coursier"),
+    },
+    linux: {
+      url: `https://github.com/coursier/coursier/releases/download/${versionPath}/cs-x86_64-pc-linux`,
+      bin: binPath("coursier"),
+    },
+    win32: {
+      url: `https://github.com/coursier/coursier/releases/download/${versionPath}/cs-x86_64-pc-win32.exe`,
+      bin: binPath("coursier.exe"),
+    },
   };
 
-  const targetFile = targets[process.platform];
-  return validBinFileExists(targetFile).then((valid) => {
-    return valid
-      ? targetFile
-      : createDir().then(() =>
-          downloadFile(urls[process.platform], targetFile)
-        );
-  });
+  const target = supportedTargets[platform];
+  if (target === undefined) {
+    return Promise.reject(`Unsupported platform ${platform}.`);
+  } else {
+    const targetFile = target.bin;
+    return validBinFileExists(targetFile).then((valid) => {
+      return valid
+        ? targetFile
+        : createDir().then(() => downloadFile(target.url, targetFile));
+    });
+  }
 }
 
 function validBinFileExists(file: string): Promise<boolean> {

tests/coursier/download-coursier.spec.ts

@@ -0,0 +1,26 @@
+import { downloadCoursierIfRequired } from "../../src/coursier/download-coursier";
+import { tmpdir } from "os";
+import { existsSync, mkdirSync, accessSync, constants, rmSync } from "fs";
+import { join } from "path";
+
+["darwin", "linux", "win32"].forEach((p) => {
+  test(
+    `download on platform: ${p}`,
+    () => {
+      const dir = join(tmpdir(), p);
+      rmSync(dir, { recursive: true, force: true });
+      mkdirSync(dir, { recursive: true });
+      return downloadCoursierIfRequired(dir, p, "v2.0.13").then((x) => {
+        expect(existsSync(x)).toBeTruthy();
+        accessSync(x, constants.X_OK);
+      });
+    },
+    25 * 1000
+  );
+});
+
+test(`fails on unknown platform`, () => {
+  return expect(
+    downloadCoursierIfRequired(tmpdir(), "unsupported", "v2.0.13")
+  ).rejects.toEqual("Unsupported platform unsupported.");
+});