Go mod: Handle multi-line error messages

go_modules/lib/dependabot/go_modules/file_updater/go_mod_updater.rb

@@ -269,22 +269,20 @@ def substitute_all(substitutions)
           write_go_mod(body)
         end
 
-        # rubocop:disable Metrics/AbcSize
-        # rubocop:disable Metrics/PerceivedComplexity
         def handle_subprocess_error(stderr)
           stderr = stderr.gsub(Dir.getwd, "")
 
           # Package version doesn't match the module major version
           error_regex = RESOLVABILITY_ERROR_REGEXES.find { |r| stderr =~ r }
           if error_regex
-            lines = stderr.lines.drop_while { |l| error_regex !~ l }
-            raise Dependabot::DependencyFileNotResolvable, lines.join
+            error_message = filter_error_message(message: stderr, regex: error_regex)
+            raise Dependabot::DependencyFileNotResolvable, error_message
           end
 
           repo_error_regex = REPO_RESOLVABILITY_ERROR_REGEXES.find { |r| stderr =~ r }
           if repo_error_regex
-            lines = stderr.lines.drop_while { |l| repo_error_regex !~ l }
-            ResolvabilityErrors.handle(lines.join, credentials: credentials)
+            error_message = filter_error_message(message: stderr, regex: repo_error_regex)
+            ResolvabilityErrors.handle(error_message, credentials: credentials)
           end
 
           path_regex = MODULE_PATH_MISMATCH_REGEXES.find { |r| stderr =~ r }
@@ -296,16 +294,22 @@ def handle_subprocess_error(stderr)
 
           out_of_disk_regex = OUT_OF_DISK_REGEXES.find { |r| stderr =~ r }
           if out_of_disk_regex
-            lines = stderr.lines.select { |l| out_of_disk_regex =~ l }
-            raise Dependabot::OutOfDisk.new, lines.join
+            error_message = filter_error_message(message: stderr, regex: out_of_disk_regex)
+            raise Dependabot::OutOfDisk.new, error_message
           end
 
           # We don't know what happened so we raise a generic error
           msg = stderr.lines.last(10).join.strip
           raise Dependabot::DependabotError, msg
         end
-        # rubocop:enable Metrics/PerceivedComplexity
-        # rubocop:enable Metrics/AbcSize
+
+        def filter_error_message(message:, regex:)
+          lines = message.lines.select { |l| regex =~ l }
+          return lines.join if lines.any?
+
+          # In case the regex is multi-line, match the whole string
+          message.match(regex).to_s
+        end
 
         def go_mod_path
           return "go.mod" if directory == "/"

go_modules/spec/dependabot/go_modules/file_updater/go_mod_updater_spec.rb

@@ -465,6 +465,39 @@
         end
       end
     end
+
+    context "for an unknown revision version" do
+      let(:project_name) { "unknown_revision_version" }
+      let(:dependency_name) do
+        "github.com/deislabs/oras"
+      end
+      let(:dependency_version) { "v0.10.0" }
+      let(:dependency_previous_version) { "v0.9.0" }
+      let(:requirements) do
+        [{
+          file: "go.mod",
+          requirement: dependency_version,
+          groups: [],
+          source: {
+            type: "default",
+            source: "github.com/deislabs/oras"
+          }
+        }]
+      end
+      let(:previous_requirements) { [] }
+
+      it "raises the correct error" do
+        error_class = Dependabot::DependencyFileNotResolvable
+        expect { updater.updated_go_sum_content }.
+          to raise_error(error_class) do |error|
+          expect(error.message).to include(
+            "go: github.com/deislabs/oras@v0.10.0 requires\n"\
+            "	github.com/docker/distribution@v0.0.0-00010101000000-000000000000: "\
+            "invalid version: unknown revision"
+          )
+        end
+      end
+    end
   end
 
   describe "#updated_go_sum_content" do

go_modules/spec/fixtures/projects/unknown_revision_version/go.mod

@@ -0,0 +1,7 @@
+module github.com/dependabot/vgotest
+
+go 1.16
+
+require (
+  github.com/deislabs/oras v0.9.0
+)

go_modules/spec/fixtures/projects/unknown_revision_version/main.go

@@ -0,0 +1,8 @@
+package main
+
+import (
+	_ "github.com/deislabs/oras"
+)
+
+func main() {
+}