dev-cmd/bump-formula-pr: use Formatter.truncate.

Add new `Formatter.truncate` method, tests and use it.

Library/Homebrew/dev-cmd/bump-formula-pr.rb

@@ -400,7 +400,7 @@ module Homebrew
             if github_release_data.present?
               pre = "pre" if github_release_data["prerelease"].present?
               # maximum length of PR body is 65,536 characters so let's truncate release notes to half of that.
-              body = github_release_data["body"].truncate(32_768)
+              body = Formatter.truncate(github_release_data["body"], max: 32_768)
 
               formula_pr_message += <<~XML
                 <details>

Library/Homebrew/test/formatter_spec.rb

@@ -110,4 +110,18 @@ RSpec.describe Formatter do
       expect(described_class.format_help_text(text, width: 80)).to eq expected
     end
   end
+
+  describe "::truncate" do
+    it "returns the original string if it's shorter than max length" do
+      expect(described_class.truncate("short", max: 10)).to eq("short")
+    end
+
+    it "truncates strings longer than max length" do
+      expect(described_class.truncate("this is a long string", max: 10)).to eq("this is...")
+    end
+
+    it "uses custom omission string" do
+      expect(described_class.truncate("this is a long string", max: 10, omission: " [...]")).to eq("this [...]")
+    end
+  end
 end

Library/Homebrew/utils/formatter.rb

@@ -54,6 +54,19 @@ module Formatter
     label(label, string, :red)
   end
 
+  # Truncate a string to a specific length.
+  #
+  # @api internal
+  sig { params(string: String, max: Integer, omission: String).returns(String) }
+  def self.truncate(string, max: 30, omission: "...")
+    return string if string.length <= max
+
+    length_with_room_for_omission = max - omission.length
+    truncated = string[0, length_with_room_for_omission]
+
+    "#{truncated}#{omission}"
+  end
+
   # Wraps text to fit within a given number of columns using regular expressions that:
   #
   # 1. convert hard-wrapped paragraphs to a single line