Allow URL-only lines to exceed TextWidth body limit

lib/overcommit/hook/commit_msg/text_width.rb

@@ -4,6 +4,11 @@ module Overcommit::Hook::CommitMsg
   # Ensures the number of columns the subject and commit message lines occupy is
   # under the preferred limits.
   class TextWidth < Base
+    # A line consisting only of a URL (optionally as a Markdown-style link
+    # reference such as `[1]: https://...`) cannot be wrapped without breaking
+    # the link, so it is exempt from the body width limit.
+    URL_ONLY_LINE = %r{\A(\[[^\]]+\]:\s*)?[a-z][a-z0-9+.-]*://\S+\z}i.freeze
+
     def run
       return :pass if empty_message?
 
@@ -42,13 +47,17 @@ def find_errors_in_body(lines)
       max_body_width = config['max_body_width']
 
       lines[2..].each_with_index do |line, index|
-        if line.chomp.size > max_body_width
-          @errors << "Line #{index + 3} of commit message has > " \
-                    "#{max_body_width} characters"
-        end
+        next if line.chomp.size <= max_body_width || url_only_line?(line)
+
+        @errors << "Line #{index + 3} of commit message has > " \
+                  "#{max_body_width} characters"
       end
     end
 
+    def url_only_line?(line)
+      URL_ONLY_LINE.match?(line.strip)
+    end
+
     def special_prefix_length(subject)
       subject.match(/^(fixup|squash)! /) { |match| match[0].length } || 0
     end

spec/overcommit/hook/commit_msg/text_width_spec.rb

@@ -73,6 +73,37 @@
     it { should warn('Line 3 of commit message has > 72 characters') }
   end
 
+  context 'when a line longer than 72 characters contains only a URL' do
+    let(:commit_msg) { <<-MSG }
+      Some summary
+
+      See:
+      https://example.com/some/very/long/path/that/cannot/be/wrapped/without/breaking/it
+    MSG
+
+    it { should pass }
+  end
+
+  context 'when a line longer than 72 characters is a link reference' do
+    let(:commit_msg) { <<-MSG }
+      Some summary
+
+      [1]: https://example.com/some/very/long/path/that/cannot/be/wrapped/without/breaking
+    MSG
+
+    it { should pass }
+  end
+
+  context 'when a line longer than 72 characters contains a URL and other text' do
+    let(:commit_msg) { <<-MSG }
+      Some summary
+
+      See https://example.com/some/very/long/path/that/cannot/be/wrapped for details
+    MSG
+
+    it { should warn('Line 3 of commit message has > 72 characters') }
+  end
+
   context 'when all lines in the message are fewer than 72 characters' do
     let(:commit_msg) { <<-MSG }
       Some summary