Merge pull request #4431 from JoeRobich/improve-invalid-mono-error

Give more information when Mono is missing or invalid.

package.json

@@ -739,7 +739,7 @@
           ],
           "default": null,
           "scope": "machine",
-          "description": "Specifies the path to a mono installation to use when \"useGlobalMono\" is set to \"always\" or \"auto\", instead of the default system one."
+          "description": "Specifies the path to a mono installation to use when \"useGlobalMono\" is set to \"always\", instead of the default system one. Example: \"/Library/Frameworks/Mono.framework/Versions/Current\""
         },
         "omnisharp.waitForDebugger": {
           "type": "boolean",
@@ -3666,4 +3666,4 @@
       ]
     }
   }
-}
+}

src/omnisharp/OmniSharpMonoResolver.ts

@@ -36,11 +36,19 @@ export class OmniSharpMonoResolver implements IMonoResolver {
 
     public async getGlobalMonoInfo(options: Options): Promise<MonoInformation> {
         let monoInfo = await this.configureEnvironmentAndGetInfo(options);
-        let isValid = monoInfo.version && satisfies(monoInfo.version, `>=${this.minimumMonoVersion}`);
 
+        let isMissing = monoInfo.version === undefined;
+        if (isMissing) {
+            const suggestedAction = options.monoPath
+                ? "Update the \"omnisharp.monoPath\" setting to point to the folder containing Mono's '/bin' folder."
+                : "Ensure that Mono's '/bin' folder is added to your environment's PATH variable.";
+            throw new Error(`Unable to find Mono. ${suggestedAction}`);
+        }
+
+        let isValid = monoInfo.version && satisfies(monoInfo.version, `>=${this.minimumMonoVersion}`);
         if (options.useGlobalMono === "always") {
             if (!isValid) {
-                throw new Error(`Cannot start OmniSharp because Mono version >=${this.minimumMonoVersion} is required.`);
+                throw new Error(`Found Mono version ${monoInfo.version}. Cannot start OmniSharp because Mono version >=${this.minimumMonoVersion} is required.`);
             }
 
             return monoInfo;