Use first SHA for last tag

Rather than having the last tag be an empty husk, generate a full
changelog link using the first sha from the repository.

Signed-off-by: Tom Duffield <tom@chef.io>

lib/github_changelog_generator/generator/generator.rb

@@ -57,14 +57,23 @@ module GitHubChangelogGenerator
     # @param [Array] pull_requests List or PR's in new section
     # @param [Array] issues List of issues in new section
     # @param [String] newer_tag Name of the newer tag. Could be nil for `Unreleased` section
-    # @param [String] older_tag_name Older tag, used for the links. Could be nil for last tag.
+    # @param [String] older_tag Older tag, used for the links. Could be nil for last tag.
     # @return [String] Ready and parsed section
-    def create_log_for_tag(pull_requests, issues, newer_tag, older_tag_name = nil)
+    def create_log_for_tag(pull_requests, issues, newer_tag, older_tag = nil)
       newer_tag_link, newer_tag_name, newer_tag_time = detect_link_tag_time(newer_tag)
 
       github_site = options[:github_site] || "https://github.com"
       project_url = "#{github_site}/#{options[:user]}/#{options[:project]}"
 
+      # If the older tag is nil, go back in time from the latest tag and find
+      # the SHA for the first commit.
+      older_tag_name =
+        if older_tag.nil?
+          @fetcher.commits_before(newer_tag_time).last["sha"]
+        else
+          older_tag["name"]
+        end
+
       log = generate_header(newer_tag_name, newer_tag_link, newer_tag_time, older_tag_name, project_url)
 
       if options[:issues]

lib/github_changelog_generator/generator/generator_generation.rb

@@ -83,14 +83,12 @@ module GitHubChangelogGenerator
     def generate_log_between_tags(older_tag, newer_tag)
       filtered_issues, filtered_pull_requests = filter_issues_for_tags(newer_tag, older_tag)
 
-      older_tag_name = older_tag.nil? ? detect_since_tag : older_tag["name"]
-
       if newer_tag.nil? && filtered_issues.empty? && filtered_pull_requests.empty?
         # do not generate empty unreleased section
         return ""
       end
 
-      create_log_for_tag(filtered_pull_requests, filtered_issues, newer_tag, older_tag_name)
+      create_log_for_tag(filtered_pull_requests, filtered_issues, newer_tag, older_tag)
     end
 
     # Apply all filters to issues and pull requests