Use exit code 1 on errors on `fnm use`. Fixes #43 (#45)

executable/Use.re

@@ -69,14 +69,27 @@ let run = (~version, ~quiet) =>
         "The following version is not installed: "
         version
       </Pastel>,
-    )
-    |> Lwt.return
+    );
+    exit(1);
+  | Dotfiles.Conflicting_Dotfiles_Found(v1, v2) =>
+    log(
+      ~quiet,
+      <Pastel color=Pastel.Red>
+        "Can't infer version from dotfiles: .node-version and .nvmrc have differing version strings:\n"
+        "  * "
+        v1
+        "\n"
+        "  * "
+        v2
+      </Pastel>,
+    );
+    exit(1);
   | Dotfiles.Version_Not_Provided =>
     log(
       ~quiet,
       <Pastel color=Pastel.Red>
         "No .nvmrc or .node-version file was found in the current directory. Please provide a version number."
       </Pastel>,
-    )
-    |> Lwt.return
+    );
+    exit(1);
   };

library/Dotfiles.re

@@ -1,4 +1,5 @@
 exception Version_Not_Provided;
+exception Conflicting_Dotfiles_Found(string, string);
 
 let versionString = fileName => {
   try%lwt (
@@ -20,9 +21,7 @@ let getVersion = () => {
   switch (nodeVersion, nvmrc) {
   | (None, None) => Lwt.fail(Version_Not_Provided)
   | (Some(v1), Some(v2)) when v1 != v2 =>
-    Lwt.fail_with(
-      "You have both .node-version and .nvmrc with differing version strings!",
-    )
+    Lwt.fail(Conflicting_Dotfiles_Found(v1, v2))
   | (Some(version), Some(_))
   | (Some(version), None)
   | (None, Some(version)) => Lwt.return(version)