[SDTEST-126] add different fallbacks for unshallowing remotes

lib/datadog/ci/git/local_repository.rb

@@ -238,23 +238,42 @@ def self.git_unshallow
           Telemetry.git_command(Ext::Telemetry::Command::UNSHALLOW)
           res = nil
 
+          unshallow_command =
+            "git fetch " \
+            "--shallow-since=\"1 month ago\" " \
+            "--update-shallow " \
+            "--filter=\"blob:none\" " \
+            "--recurse-submodules=no " \
+            "$(git config --default origin --get clone.defaultRemoteName)"
+
+          unshallow_remotes = [
+            "$(git rev-parse HEAD)",
+            "$(git rev-parse --abbrev-ref --symbolic-full-name @{upstream})",
+            nil
+          ]
+
           duration_ms = Core::Utils::Time.measure(:float_millisecond) do
-            res = exec_git_command(
-              "git fetch " \
-              "--shallow-since=\"1 month ago\" " \
-              "--update-shallow " \
-              "--filter=\"blob:none\" " \
-              "--recurse-submodules=no " \
-              "$(git config --default origin --get clone.defaultRemoteName) $(git rev-parse HEAD)"
-            )
+            unshallow_remotes.each do |remote|
+              unshallowing_errored = false
+
+              res =
+                begin
+                  exec_git_command(
+                    "#{unshallow_command} #{remote}"
+                  )
+                rescue => e
+                  log_failure(e, "git unshallow")
+                  telemetry_track_error(e, Ext::Telemetry::Command::UNSHALLOW)
+                  unshallowing_errored = true
+                  nil
+                end
+
+              break unless unshallowing_errored
+            end
           end
-          Telemetry.git_command_ms(Ext::Telemetry::Command::UNSHALLOW, duration_ms)
 
+          Telemetry.git_command_ms(Ext::Telemetry::Command::UNSHALLOW, duration_ms)
           res
-        rescue => e
-          log_failure(e, "git unshallow")
-          telemetry_track_error(e, Ext::Telemetry::Command::UNSHALLOW)
-          nil
         end
 
         # makes .exec_git_command private to make sure that this method

spec/datadog/ci/git/local_repository_spec.rb

@@ -305,10 +305,34 @@ def with_clone_git_dir
           with_clone_git_dir { described_class.git_commits }
         end
 
-        it "unshallows the repository" do
-          expect(subject).to be_truthy
-          # additional commits plus the initial commit
-          expect(commits.size).to eq(commits_count + 1)
+        context "successful from the first try" do
+          before do
+            expect(Open3).to receive(:capture2e).and_call_original.at_most(2).times
+          end
+
+          it "unshallows the repository" do
+            expect(subject).to be_truthy
+            # additional commits plus the initial commit
+            expect(commits.size).to eq(commits_count + 1)
+          end
+        end
+
+        context "when unshallow command fails" do
+          before do
+            allow(Open3).to receive(:capture2e).and_call_original
+            allow(Open3).to receive(:capture2e)
+              .with("git fetch --shallow-since=\"1 month ago\" --update-shallow --filter=\"blob:none\" --recurse-submodules=no $(git config --default origin --get clone.defaultRemoteName) $(git rev-parse HEAD)", stdin_data: nil)
+              .and_return(["error", double(success?: false, to_i: 1)])
+          end
+
+          it "still unshallows the repository using the fallback command" do
+            expect(subject).to be_truthy
+            # additional commits plus the initial commit
+            expect(commits.size).to eq(commits_count + 1)
+          end
+
+          # it signals error to the telemetry
+          it_behaves_like "emits telemetry metric", :inc, "git.command_errors", 1
         end
       end
     end