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

lib/github_changelog_generator/octo_fetcher.rb

@@ -236,6 +236,17 @@ Make sure, that you push tags to remote repo via 'git push --tags'"
       end
     end
 
+    # Fetch all commits before certain point
+    #
+    # @return [String]
+    def commits_before(start_time)
+      commits = []
+      iterate_pages(@client, "commits_before", start_time.to_datetime.to_s) do |new_commits|
+        commits.concat(new_commits)
+      end
+      commits
+    end
+
     private
 
     def stringify_keys_deep(indata)

spec/unit/octo_fetcher_spec.rb

@@ -526,4 +526,18 @@ describe GitHubChangelogGenerator::OctoFetcher do
       end
     end
   end
+
+  describe "#commits_before" do
+    context "when API is valid", :vcr do
+      let(:start_time) { Time.parse("Wed Mar 4 18:47:17 2015 +0200") }
+
+      subject do
+        fetcher.commits_before(start_time)
+      end
+
+      it "returns commits" do
+        expect(subject.last["sha"]).to eq("4c2d6d1ed58bdb24b870dcb5d9f2ceed0283d69d")
+      end
+    end
+  end
 end