workaround link(pkg) twice at once

README.md

@@ -57,12 +57,14 @@ const { pkgs: tree } = await hydrate(pkg)
 const { installed, pending } = await resolve(tree)
 
 for (const pkg of pending) {
-  const install = await install(pkg)
+  const installation = await install(pkg)
   // ^^ install packages that aren’t yet installed
   // ^^ takes a logger parameter so you can show progress to the user
   // ^^ you could do these in parallel to speed things up
   // ^^ by default, versioned installs go to ~/.tea, separated from the user’s system. The install location can be customized, see next section.
-  installed.push(install)
+  await link(installation)
+  // ^^ creates v*, vx, vx.y symlinks ∵ some packages depend on this
+  installed.push(installation)
 }
 
 const { map, flatten } = useShellEnv()

src/prefab/install.test.ts

@@ -24,7 +24,8 @@ Deno.test("install()", async runner => {
     assertEquals(installation.pkg.version, pkg.version)
     assertEquals(installation.path, conf.prefix.join(pkg.project, `v${pkg.version}`))
 
-    installation.path.rm({ recursive: true  })
+    /// so next test works
+    installation.path.rm({ recursive: true })
 
     stubber.restore()
   })

src/prefab/link.test.ts

@@ -0,0 +1,37 @@
+import { useTestConfig } from "../hooks/useConfig.test.ts"
+import { assert } from "deno/testing/asserts.ts"
+import SemVer from "../utils/semver.ts"
+import { Package } from "../types.ts"
+import install from "./install.ts"
+import link from "./link.ts";
+
+Deno.test("link()", async runner => {
+  const pkg: Package = {
+    project: "tea.xyz/brewkit",
+    version: new SemVer("0.30.0")
+  }
+
+  await runner.step("link()", async () => {
+    useTestConfig()
+
+    const installation = await install(pkg)
+    await link(installation)
+    await link(installation)  // calling twice works
+
+    /// test symlinks work
+    assert(installation.path.parent().join("v*").isDirectory())
+    assert(installation.path.parent().join(`v${pkg.version.major}`).isDirectory())
+  })
+
+  await runner.step("link() ×2 at once", async () => {
+    const installation = await install(pkg)
+    const p1 = link(installation)
+    const p2 = link(installation)
+
+    await Promise.all([p1, p2])
+
+    /// test symlinks work
+    assert(installation.path.parent().join("v*").isDirectory())
+    assert(installation.path.parent().join(`v${pkg.version.major}`).isDirectory())
+  })
+})

src/prefab/link.ts

@@ -43,9 +43,19 @@ export default async function link(pkg: Package | Installation) {
   }
 
   async function makeSymlink(symname: string) {
-    await Deno.symlink(
-      installation.path.basename(),
-      shelf.join(symname).rm().string,
-      {type: 'dir'})
+    try {
+      await Deno.symlink(
+        installation.path.basename(),  // makes it relative
+        shelf.join(symname).rm().string,
+        {type: 'dir'})
+      } catch (err) {
+        if (err instanceof Deno.errors.AlreadyExists) {
+          //FIXME race condition for installing the same pkg simultaneously
+          // real fix is to lock around the entire download/untar/link process
+          return
+        } else {
+          throw err
+        }
+      }
   }
 }