Fix crash in oneshot coverage when file is missing or not valid Ruby

lib/simplecov/result_adapter.rb

@@ -31,16 +31,18 @@ def adapt
   private
 
     def adapt_oneshot_lines_if_needed(file_name, cover_statistic)
-      if cover_statistic.key?(:oneshot_lines)
-        line_stub = Coverage.line_stub(file_name)
-        oneshot_lines = cover_statistic.delete(:oneshot_lines)
-        oneshot_lines.each do |covered_line|
-          line_stub[covered_line - 1] = 1
-        end
-        cover_statistic[:lines] = line_stub
-      else
-        cover_statistic
+      return unless cover_statistic.key?(:oneshot_lines)
+
+      oneshot_lines = cover_statistic.delete(:oneshot_lines)
+      line_stub = begin
+        Coverage.line_stub(file_name)
+      rescue Errno::ENOENT, SyntaxError
+        Array.new(oneshot_lines.max || 0, nil)
+      end
+      oneshot_lines.each do |covered_line|
+        line_stub[covered_line - 1] = 1
       end
+      cover_statistic[:lines] = line_stub
     end
   end
 end

spec/result_adapter_spec.rb

@@ -0,0 +1,84 @@
+# frozen_string_literal: true
+
+require "helper"
+require "coverage"
+
+describe SimpleCov::ResultAdapter do
+  subject { described_class.call(result_set) }
+
+  let(:existing_file) { source_fixture("app/models/user.rb") }
+
+  describe "with oneshot_lines coverage" do
+    before do
+      skip "oneshot_lines coverage not supported" if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.6") || RUBY_ENGINE == "truffleruby"
+    end
+
+    context "when all tracked files exist" do
+      let(:result_set) do
+        {
+          existing_file => {oneshot_lines: [2, 3, 4]}
+        }
+      end
+
+      it "adapts the coverage data to lines format" do
+        lines = subject[existing_file][:lines]
+        expect(lines).to be_an(Array)
+        expect(lines[1]).to eq(1)
+        expect(lines[2]).to eq(1)
+        expect(lines[3]).to eq(1)
+      end
+    end
+
+    context "when a tracked file no longer exists on disk" do
+      let(:deleted_file) { File.join(SimpleCov.root, "lib/deleted_generated_file.rb") }
+
+      let(:result_set) do
+        {
+          existing_file => {oneshot_lines: [2, 3]},
+          deleted_file => {oneshot_lines: [1, 3]}
+        }
+      end
+
+      it "builds a fallback line stub for the missing file" do
+        lines = subject[deleted_file][:lines]
+        expect(lines[0]).to eq(1)
+        expect(lines[2]).to eq(1)
+      end
+
+      it "still adapts the existing file normally" do
+        lines = subject[existing_file][:lines]
+        expect(lines[1]).to eq(1)
+        expect(lines[2]).to eq(1)
+      end
+    end
+
+    context "when a tracked file is not valid Ruby" do
+      let(:non_ruby_file) { source_fixture("non_ruby_config.yml") }
+
+      before do
+        File.write(non_ruby_file, "development: &default\n  adapter: mysql2\n")
+      end
+
+      after do
+        FileUtils.rm_f(non_ruby_file)
+      end
+
+      let(:result_set) do
+        {
+          existing_file => {oneshot_lines: [2]},
+          non_ruby_file => {oneshot_lines: [1]}
+        }
+      end
+
+      it "builds a fallback line stub for the non-parseable file" do
+        lines = subject[non_ruby_file][:lines]
+        expect(lines[0]).to eq(1)
+      end
+
+      it "still adapts the existing file normally" do
+        lines = subject[existing_file][:lines]
+        expect(lines[1]).to eq(1)
+      end
+    end
+  end
+end