Repository: serverless/serverless (JavaScript) — Bug Fix

Issue:
`sls plugin install` failing
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# This is a Bug Report

## Description

* What went wrong?
I wanted to install a serverless plugin through the CLI ` $ sls plugin install serverless-express`  but was met with an error `  Serverless command "plugin install serverless-express" not found. Did you mean "uninstall"? Run "serverless help" for a list of all available commands.`
* What did you expect should have happened?
I expected based on the following that I could use the `sls` command line to install a plugin. I normally just install by adding it to my `serverless.yml` and using, but I gave this a try for the first time and it wasn't as I expected
```bash
tyler:~/environment/sls-starters/sls-express (master) $ sls help | grep plugin
* Pass "--verbose" to this command to get in-depth plugin info
install ....................... Install a Serverless service from GitHub or a plugin from the Serverless registry
plugin ........................ Plugin management for Serverless
plugin install ................ Install and add a plugin to your service
plugin uninstall .............. Uninstall and remove a plugin from your service
plugin list ................... Lists all available plugins
plugin search ................. Search for plugins
tyler:~/environment/sls-starters/sls-express (master) $ sls plugin list | grep serverless-express
serverless-express - Making express app development compatible with serverless framework.
tyler:~/environment/sls-starters/sls-express (master) $ sls plugin install serverless-express

  Serverless Error ---------------------------------------

  Serverless command "plugin install serverless-express" not found. Did you mean "uninstall"? Run "serverless help" for a list of all available commands.

  Get Support --------------------------------------------
     Docs:          docs.serverless.com
     Bugs:          github.com/serverless/serverless/issues
     Issues:        forum.serverless.com
 
  Your Environment Information ---------------------------
     OS:                     linux
     Node Version:           8.10.0
     Serverless Version:     1.41.0
 
tyler:~/environment/sls-starters/sls-express (master) $ sls plugin install help                                                                                            
 
  Serverless Error ---------------------------------------
 
  Serverless command "plugin install help" not found. Did you mean "uninstall"? Run "serverless help" for a list of all available commands.
 
  Get Support --------------------------------------------
     Docs:          docs.serverless.com
     Bugs:          github.com/serverless/serverless/issues
     Issues:        forum.serverless.com
 
  Your Environment Information ---------------------------
     OS:                     linux
     Node Version:           8.10.0
     Serverless Version:     1.41.0
```
 
* What was the config you used?
Basic starter from `$ serverless create --template aws-nodejs --path my-service` no custom config. `serverless.yml` here 
```yml
service: sls-express 
provider:
  name: aws
  runtime: nodejs8.10
functions:
  hello:
    handler: handler.hello
```

* What stacktrace or error message from your provider did you see?
```bash
  Serverless Error ---------------------------------------

  Serverless command "plugin install serverless-express" not found. Did you mean "uninstall"? Run "serverless help" for a list of all available commands.

  Get Support --------------------------------------------
     Docs:          docs.serverless.com
     Bugs:          github.com/serverless/serverless/issues
     Issues:        forum.serverless.com
 
  Your Environment Information ---------------------------
     OS:                     linux
     Node Version:           8.10.0
     Serverless Version:     1.41.0
 
```
Similar or dependent issues:
* #4258

## Additional Data

* ***Serverless Framework Version you're using***:
1.41.0
* ***Operating System***:
Amazon Linux inside an EC2 using Cloud9
* ***Stack Trace***:
N/A
* ***Provider Error messages***:
```bash

  Serverless Error ---------------------------------------

  Serverless command "plugin install serverless-express" not found. Did you mean "uninstall"? Run "serverless help" for a list of all available commands.

  Get Support --------------------------------------------
     Docs:          docs.serverless.com
     Bugs:          github.com/serverless/serverless/issues
     Issues:        forum.serverless.com
 
  Your Environment Information ---------------------------
     OS:                     linux
     Node Version:           8.10.0
     Serverless Version:     1.41.0

```


Discussion:
Ahh I see what I did wrong. I searched for plugins with `$ sls plugin list | grep serverless-express` I didn't use `$ sls plugin search --query express`. 

The `plugin search` command tells you that you should 
```
To install a plugin run 'serverless plugin install --name plugin-name-here'

It will be automatically downloaded and added to your package.json and serverless.yml file
```

When I did `$ sls plugin install --name serverless-express` it worked like a charm. 
I'll be closing this issue and opening up a feature request for the `$ sls plugin install` utility

Resolving patch:
diff --git a/lib/classes/PluginManager.js b/lib/classes/PluginManager.js
index ebe0d2e45be..433e3dac735 100644
--- a/lib/classes/PluginManager.js
+++ b/lib/classes/PluginManager.js
@@ -359,6 +359,20 @@ class PluginManager {
         && (isNotEntrypoint || allowEntryPoints)) {
         return current.commands[name];
       }
+      // if user is using a top level command properly, but sub commands are not
+      if (this.serverless.cli.loadedCommands[commandOrAlias[0]]) {
+        const errorMessage = [`"${name}" is not a valid sub command. Run "serverless `];
+        for (let i = 0; commandOrAlias[i] !== name; i++) {
+          errorMessage.push(`${commandOrAlias[i]}`);
+          if (commandOrAlias[i + 1] !== name) {
+            errorMessage.push(' ');
+          }
+        }
+        errorMessage.push('" to see a more helpful error message for this command.');
+        throw new this.serverless.classes.Error(errorMessage.join(''));
+      }
+
+      // top level command isn't valid. give a suggestion
       const commandName = commandOrAlias.slice(0, index + 1).join(' ');
       const suggestedCommand = getCommandSuggestion(commandName,
         this.serverless.cli.loadedCommands);


Test patch:
diff --git a/lib/classes/PluginManager.test.js b/lib/classes/PluginManager.test.js
index 595c2caf6c2..b1a9a14c5ce 100644
--- a/lib/classes/PluginManager.test.js
+++ b/lib/classes/PluginManager.test.js
@@ -1586,6 +1586,107 @@ describe('PluginManager', () => {
     });
   });
 
+  describe('#getCommand()', () => {
+    beforeEach(() => {
+      pluginManager.addPlugin(SynchronousPluginMock);
+      pluginManager.serverless.cli.loadedCommands = {
+        create: {
+          usage: 'Create new Serverless service',
+          lifecycleEvents: [
+            'create',
+          ],
+          options: {
+            template: {
+              usage: 'Template for the service. Available templates: ", "aws-nodejs", "..."',
+              shortcut: 't',
+            },
+          },
+          key: 'create',
+          pluginName: 'Create',
+        },
+        deploy: {
+          usage: 'Deploy a Serverless service',
+          configDependent: true,
+          lifecycleEvents: [
+            'cleanup',
+            'initialize',
+          ],
+          options: {
+            conceal: {
+              usage: 'Hide secrets from the output (e.g. API Gateway key values)',
+            },
+            stage: {
+              usage: 'Stage of the service',
+              shortcut: 's',
+            },
+          },
+          key: 'deploy',
+          pluginName: 'Deploy',
+          commands: {
+            function: {
+              usage: 'Deploy a single function from the service',
+              lifecycleEvents: [
+                'initialize',
+                'packageFunction',
+                'deploy',
+              ],
+              options: {
+                function: {
+                  usage: 'Name of the function',
+                  shortcut: 'f',
+                  required: true,
+                },
+              },
+              key: 'deploy:function',
+              pluginName: 'Deploy',
+            },
+            list: {
+              usage: 'List deployed version of your Serverless Service',
+              lifecycleEvents: [
+                'log',
+              ],
+              key: 'deploy:list',
+              pluginName: 'Deploy',
+              commands: {
+                functions: {
+                  usage: 'List all the deployed functions and their versions',
+                  lifecycleEvents: [
+                    'log',
+                  ],
+                  key: 'deploy:list:functions',
+                  pluginName: 'Deploy',
+                },
+              },
+            },
+          },
+        },
+      };
+    });
+    it('should give a suggestion for an unknown command', (done) => {
+      try {
+        pluginManager.getCommand(['creet']);
+        done('Test failed. Expected an error to be thrown');
+      } catch (error) {
+        expect(error.name).to.eql('ServerlessError');
+        expect(error.message).to.eql('Serverless command "creet" not found. ' +
+          'Did you mean "create"? Run "serverless help" for a list of all available commands.');
+        done();
+      }
+    });
+
+    it('should not give a suggestion for valid top level command', (done) => {
+      try {
+        pluginManager.getCommand(['deploy', 'function-misspelled']);
+        done('Test failed. Expected an error to be thrown');
+      } catch (error) {
+        expect(error.name).to.eql('ServerlessError');
+        expect(error.message).to.eql('"function-misspelled" is not a valid sub command. '
+          + 'Run "serverless deploy" to see a more helpful error message for this command.');
+        done();
+      }
+    });
+  });
+
   describe('#spawn()', () => {
     it('should throw an error when the given command is not available', () => {
       pluginManager.addPlugin(EntrypointPluginMock);