From 311cb9fbe94fe09c0dc08a52f5bff169529960ba Mon Sep 17 00:00:00 2001
From: William Woodruff <william@tuffbizz.com>
Date: Fri, 29 Sep 2017 18:31:28 -0400
Subject: Support for required options

This commit introduces support for required options,
which are options that cause the parser to raise
a `MissingRequiredOption` exception if not present.

Options can be marked as required by passing
`required: true` in their configuration, and any errors
caused by missing required options can be suppressed via
`suppress_errors: true`.
---
 README.md          |  2 ++
 lib/slop/error.rb  |  5 +++++
 lib/slop/option.rb |  6 ++++++
 lib/slop/parser.rb |  9 +++++++++
 test/error_test.rb | 14 ++++++++++++++
 5 files changed, 36 insertions(+)

diff --git a/README.md b/README.md
index 505d4c5..4d686ce 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,7 @@ Usage
 opts = Slop.parse do |o|
   o.string '-h', '--host', 'a hostname'
   o.integer '--port', 'custom port', default: 80
+  o.string '-l', '--login', required: true
   o.bool '-v', '--verbose', 'enable verbose mode'
   o.bool '-q', '--quiet', 'suppress output (quiet mode)'
   o.bool '-c', '--check-ssl-certificate', 'check SSL certificate for host'
@@ -197,6 +198,7 @@ Slop will raise errors for the following:
 
 * An option used without an argument when it expects one: `Slop::MissingArgument`
 * An option used that Slop doesn't know about: `Slop::UnknownOption`
+* An option marked as `required` when not provided: `Slop::MissingRequiredOption`
 
 These errors inherit from `Slop::Error`, so you can rescue them all.
 Alternatively you can suppress these errors with the `suppress_errors` config
diff --git a/lib/slop/error.rb b/lib/slop/error.rb
index b02de3b..e024645 100644
--- a/lib/slop/error.rb
+++ b/lib/slop/error.rb
@@ -32,4 +32,9 @@ module Slop
       @flag = flag
     end
   end
+
+  # Raised when a required option is *not* parsed.
+  # Suppress with the `suppress_errors` config option.
+  class MissingRequiredOption < Error
+  end
 end
diff --git a/lib/slop/option.rb b/lib/slop/option.rb
index b8533ae..093b37f 100644
--- a/lib/slop/option.rb
+++ b/lib/slop/option.rb
@@ -4,6 +4,7 @@ module Slop
       help: true,
       tail: false,
       underscore_flags: true,
+      required: false,
     }
 
     # An Array of flags this option matches.
@@ -101,6 +102,11 @@ module Slop
       config[:suppress_errors]
     end
 
+    # Returns true if an exception should be raised when this option isn't supplied.
+    def required?
+      config[:required]
+    end
+
     # Returns all flags joined by a comma. Used by the help string.
     def flag
       flags.join(", ")
diff --git a/lib/slop/parser.rb b/lib/slop/parser.rb
index 3cba82b..463e75a 100644
--- a/lib/slop/parser.rb
+++ b/lib/slop/parser.rb
@@ -80,6 +80,15 @@ module Slop
 
       @arguments += ignored_args
 
+      if !suppress_errors?
+        unused_options.each do |o|
+          if o.config[:required]
+            pretty_flags = o.flags.map { |f| "`#{f}'" }.join(", ")
+            raise MissingRequiredOption, "missing required option #{pretty_flags}"
+          end
+        end
+      end
+
       Result.new(self).tap do |result|
         used_options.each { |o| o.finish(result) }
       end
diff --git a/test/error_test.rb b/test/error_test.rb
index 2f7730b..d9c71ab 100644
--- a/test/error_test.rb
+++ b/test/error_test.rb
@@ -49,3 +49,17 @@ describe Slop::UnknownOption do
     opts.parse %w(--foo)
   end
 end
+
+describe Slop::MissingRequiredOption do
+  it "raises when a required option is missing" do
+    opts = Slop::Options.new
+    opts.string "-n", "--name", required: true
+    assert_raises(Slop::MissingRequiredOption) { opts.parse [] }
+  end
+
+  it "does not raise when errors are suppressed" do
+    opts = Slop::Options.new(suppress_errors: true)
+    opts.string "-n", "--name", required: true
+    opts.parse []
+  end
+end
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