Fix acronym support in humanize

Acronym inflections are stored with lowercase keys in the hash but
the match wasn't being lowercased before being looked up in the hash.
This shouldn't have any performance impact because before it would
fail to find the acronym and perform the `downcase` operation anyway.

Fixes #31052.

activesupport/CHANGELOG.md

@@ -1,3 +1,14 @@
+*   Fix acronym support in `humanize`
+
+    Acronym inflections are stored with lowercase keys in the hash but
+    the match wasn't being lowercased before being looked up in the hash.
+    This shouldn't have any performance impact because before it would
+    fail to find the acronym and perform the `downcase` operation anyway.
+
+    Fixes #31052.
+
+    *Andrew White*
+
 *   Add same method signature for `Time#prev_year` and `Time#next_year`
     in accordance with `Date#prev_year`, `Date#next_year`.
 

activesupport/lib/active_support/inflector/methods.rb

@@ -138,7 +138,7 @@ def humanize(lower_case_and_underscored_word, capitalize: true, keep_id_suffix:
       result.tr!("_".freeze, " ".freeze)
 
       result.gsub!(/([a-z\d]*)/i) do |match|
-        "#{inflections.acronyms[match] || match.downcase}"
+        "#{inflections.acronyms[match.downcase] || match.downcase}"
       end
 
       if capitalize

activesupport/test/inflector_test.rb

@@ -356,6 +356,19 @@ def test_humanize_by_string
     assert_equal("Col rpted bugs", ActiveSupport::Inflector.humanize("COL_rpted_bugs"))
   end
 
+  def test_humanize_with_acronyms
+    ActiveSupport::Inflector.inflections do |inflect|
+      inflect.acronym "LAX"
+      inflect.acronym "SFO"
+    end
+    assert_equal("LAX roundtrip to SFO", ActiveSupport::Inflector.humanize("LAX ROUNDTRIP TO SFO"))
+    assert_equal("LAX roundtrip to SFO", ActiveSupport::Inflector.humanize("LAX ROUNDTRIP TO SFO", capitalize: false))
+    assert_equal("LAX roundtrip to SFO", ActiveSupport::Inflector.humanize("lax roundtrip to sfo"))
+    assert_equal("LAX roundtrip to SFO", ActiveSupport::Inflector.humanize("lax roundtrip to sfo", capitalize: false))
+    assert_equal("LAX roundtrip to SFO", ActiveSupport::Inflector.humanize("Lax Roundtrip To Sfo"))
+    assert_equal("LAX roundtrip to SFO", ActiveSupport::Inflector.humanize("Lax Roundtrip To Sfo", capitalize: false))
+  end
+
   def test_constantize
     run_constantize_tests_on do |string|
       ActiveSupport::Inflector.constantize(string)