Handle all YAML parser exceptions in .gitlab-ci.yml (fixes #41209)

- Move the exception handling as close to the source as possible to
avoid leaking Psych ahstraction
- Also remove unnecessary rescue all statement from LintsController.
This should not be necessary anymore since any YAML errors should all be
caught by the #validation_message method.

app/controllers/ci/lints_controller.rb

@@ -16,10 +16,7 @@ module Ci
         @builds = @config_processor.builds
         @jobs = @config_processor.jobs
       end
-    rescue
-      @error = 'Undefined error'
-      @status = false
-    ensure
+
       render :show
     end
   end

app/models/ci/pipeline.rb

@@ -394,7 +394,7 @@ module Ci
       @config_processor ||= begin
         Gitlab::Ci::YamlProcessor.new(ci_yaml_file)
-      rescue Gitlab::Ci::YamlProcessor::ValidationError, Psych::SyntaxError => e
+      rescue Gitlab::Ci::YamlProcessor::ValidationError => e
         self.yaml_errors = e.message
         nil
       rescue

changelogs/unreleased/41209-ci-linter-fails-on-gitlab-ci-blob-viewer.yml

+---
+title: 'Handle all Psych YAML parser exceptions (fixes #41209)'
+merge_request:
+author:
+type: fixed

lib/gitlab/ci/config/loader.rb

@@ -6,6 +6,8 @@ module Gitlab
         def initialize(config)
           @config = YAML.safe_load(config, [Symbol], [], true)
+        rescue Psych::Exception => e
+          raise FormatError, e.message
         end
         def valid?

lib/gitlab/ci/yaml_processor.rb

@@ -85,7 +85,7 @@ module Gitlab
         begin
           Gitlab::Ci::YamlProcessor.new(content)
           nil
-        rescue ValidationError, Psych::SyntaxError => e
+        rescue ValidationError => e
           e.message
         end
       end

spec/lib/gitlab/ci/config/loader_spec.rb

@@ -38,6 +38,16 @@ describe Gitlab::Ci::Config::Loader do
     end
   end
+  context 'when there is an unknown alias' do
+    let(:yml) { 'steps: *bad_alias' }
+
+    describe '#initialize' do
+      it 'raises FormatError' do
+        expect { loader }.to raise_error(Gitlab::Ci::Config::Loader::FormatError, 'Unknown alias: bad_alias')
+      end
+    end
+  end
+
   context 'when yaml config is empty' do
     let(:yml) { '' }

spec/lib/gitlab/ci/yaml_processor_spec.rb

@@ -1394,7 +1394,7 @@ EOT
       describe "Error handling" do
         it "fails to parse YAML" do
-          expect {Gitlab::Ci::YamlProcessor.new("invalid: yaml: test")}.to raise_error(Psych::SyntaxError)
+          expect {Gitlab::Ci::YamlProcessor.new("invalid: yaml: test")}.to raise_error(Gitlab::Ci::YamlProcessor::ValidationError)
         end
         it "indicates that object is invalid" do
@@ -1688,37 +1688,35 @@ EOT
       end
       describe "#validation_message" do
+        subject { Gitlab::Ci::YamlProcessor.validation_message(content) }
+
         context "when the YAML could not be parsed" do
-          it "returns an error about invalid configutaion" do
-            content = YAML.dump("invalid: yaml: test")
-            expect(Gitlab::Ci::YamlProcessor.validation_message(content))
-              .to eq "Invalid configuration format"
-          end
+          let(:content) { YAML.dump("invalid: yaml: test") }
+          it { is_expected.to eq "Invalid configuration format" }
         end
         context "when the tags parameter is invalid" do
-          it "returns an error about invalid tags" do
-            content = YAML.dump({ rspec: { script: "test", tags: "mysql" } })
-            expect(Gitlab::Ci::YamlProcessor.validation_message(content))
-              .to eq "jobs:rspec tags should be an array of strings"
-          end
+          let(:content) { YAML.dump({ rspec: { script: "test", tags: "mysql" } }) }
+          it { is_expected.to eq "jobs:rspec tags should be an array of strings" }
         end
         context "when YAML content is empty" do
-          it "returns an error about missing content" do
-            expect(Gitlab::Ci::YamlProcessor.validation_message(''))
-              .to eq "Please provide content of .gitlab-ci.yml"
-          end
+          let(:content) { '' }
+          it { is_expected.to eq "Please provide content of .gitlab-ci.yml" }
+        end
+
+        context 'when the YAML contains an unknown alias' do
+          let(:content) { 'steps: *bad_alias' }
+
+          it { is_expected.to eq "Unknown alias: bad_alias" }
         end
         context "when the YAML is valid" do
-          it "does not return any errors" do
-            content = File.read(Rails.root.join('spec/support/gitlab_stubs/gitlab_ci.yml'))
-            expect(Gitlab::Ci::YamlProcessor.validation_message(content)).to be_nil
-          end
+          let(:content) { File.read(Rails.root.join('spec/support/gitlab_stubs/gitlab_ci.yml')) }
+          it { is_expected.to be_nil }
         end
       end