Write parser output only after successful generation

lib/lrama/command.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "stringio"
+
 module Lrama
   class Command
     LRAMA_LIB = File.realpath(File.join(File.dirname(__FILE__)))
@@ -33,8 +35,8 @@ def execute_command_workflow
       render_reports(states) if @options.report_file
       @tracer.trace(grammar)
       render_diagram(grammar)
-      render_output(context, grammar)
       states.validate!(@logger)
+      render_output(context, grammar)
       @warnings.warn(grammar, states)
     end
 
@@ -103,18 +105,18 @@ def render_diagram(grammar)
     end
 
     def render_output(context, grammar)
-      File.open(@options.outfile, "w+") do |f|
-        Lrama::Output.new(
-          out: f,
-          output_file_path: @options.outfile,
-          template_name: @options.skeleton,
-          grammar_file_path: @options.grammar_file,
-          header_file_path: @options.header_file,
-          context: context,
-          grammar: grammar,
-          error_recovery: @options.error_recovery,
-        ).render
-      end
+      out = StringIO.new
+      Lrama::Output.new(
+        out: out,
+        output_file_path: @options.outfile,
+        template_name: @options.skeleton,
+        grammar_file_path: @options.grammar_file,
+        header_file_path: @options.header_file,
+        context: context,
+        grammar: grammar,
+        error_recovery: @options.error_recovery,
+      ).render
+      File.write(@options.outfile, out.string)
     end
   end
 end

spec/lrama/command_spec.rb

@@ -81,5 +81,49 @@
         File.delete("report.output")
       end
     end
+
+    context "when conflicts do not match %expect" do
+      it "does not create the parser output" do
+        grammar = <<~Y
+          %expect 0
+          %token NUM
+          %%
+          expr: NUM | expr '+' expr;
+        Y
+
+        Dir.mktmpdir do |dir|
+          outfile = File.join(dir, "parse.c")
+          allow(STDIN).to receive(:read).and_return(grammar)
+          command = Lrama::Command.new(["-o", outfile, "-", "conflict.y"])
+          errors = StringIO.new
+          command.instance_variable_set(:@logger, Lrama::Logger.new(errors))
+
+          expect { command.run }.to raise_error(SystemExit)
+          expect(errors.string).to eq("error: shift/reduce conflicts: 1 found, 0 expected\n")
+          expect(File).not_to exist(outfile)
+        end
+      end
+    end
+
+    context "when rendering fails" do
+      it "preserves the existing parser output" do
+        Dir.mktmpdir do |dir|
+          outfile = File.join(dir, "parse.c")
+          File.write(outfile, "existing output")
+          command = Lrama::Command.new(["-o", outfile, fixture_path("command/basic.y")])
+          allow(Lrama::Output).to receive(:new) do |out:, **|
+            output = instance_double(Lrama::Output)
+            allow(output).to receive(:render) do
+              out << "partial output"
+              raise "render failed"
+            end
+            output
+          end
+
+          expect { command.run }.to raise_error("render failed")
+          expect(File.read(outfile)).to eq("existing output")
+        end
+      end
+    end
   end
 end