1 files changed, 42 insertions, 3 deletions
diff --git a/danger/commit_messages/Dangerfile b/danger/commit_messages/Dangerfile
index e982e8ed7c5..c5ebb9b457e 100644
--- a/danger/commit_messages/Dangerfile
+++ b/danger/commit_messages/Dangerfile
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'json'
+
 # rubocop: disable Style/SignalException
 # rubocop: disable Metrics/CyclomaticComplexity
 # rubocop: disable Metrics/PerceivedComplexity
@@ -8,10 +10,38 @@
 # https://github.com/jonallured/danger-commit_lint because its output is not
 # very helpful, and it doesn't offer the means of ignoring merge commits.
 
+class EmojiChecker
+  DIGESTS = File.expand_path('../../fixtures/emojis/digests.json', __dir__)
+  ALIASES = File.expand_path('../../fixtures/emojis/aliases.json', __dir__)
+
+  # A regex that indicates a piece of text _might_ include an Emoji. The regex
+  # alone is not enough, as we'd match `:foo:bar:baz`. Instead, we use this
+  # regex to save us from having to check for all possible emoji names when we
+  # know one definitely is not included.
+  LIKELY_EMOJI = /:[\+a-z0-9_\-]+:/
+
+  def initialize
+    names = JSON.parse(File.read(DIGESTS)).keys +
+      JSON.parse(File.read(ALIASES)).keys
+
+    @emoji = names.map { |name| ":#{name}:" }
+  end
+
+  def includes_emoji?(text)
+    return false unless text.match?(LIKELY_EMOJI)
+
+    @emoji.any? { |emoji| text.include?(emoji) }
+  end
+end
+
 def fail_commit(commit, message)
   fail("#{commit.sha}: #{message}")
 end
 
+def warn_commit(commit, message)
+  warn("#{commit.sha}: #{message}")
+end
+
 def lines_changed_in_commit(commit)
   commit.diff_parent.stats[:total][:lines]
 end
@@ -33,6 +63,7 @@ end
 
 def lint_commits(commits)
   failures = false
+  emoji_checker = EmojiChecker.new
 
   unicode_emoji_regex = %r((
     [\u{1F300}-\u{1F5FF}] |
@@ -60,13 +91,21 @@ def lint_commits(commits)
       failures = true
     end
 
-    if subject.length > 50
+    if subject.length > 72
       fail_commit(
         commit,
-        'The commit subject may not be longer than 50 characters'
+        'The commit subject may not be longer than 72 characters'
       )
 
       failures = true
+    elsif subject.length > 50
+      warn_commit(
+        commit,
+        "This commit's subject line could be improved. " \
+          'Commit subjects are ideally no longer than roughly 50 characters, ' \
+          'though we allow up to 72 characters in the subject. ' \
+          'If possible, try to reduce the length of the subject to roughly 50 characters.'
+      )
     end
 
     unless subject_starts_with_capital?(subject)
@@ -117,7 +156,7 @@ def lint_commits(commits)
       failures = true
     end
 
-    if commit.message.match?(/:[\+a-z0-9_\-]+:/)
+    if emoji_checker.includes_emoji?(commit.message)
       fail_commit(
         commit,
         'Avoid the use of Markdown Emoji such as `:+1:`. ' \