Warn on shift/reduce conflicts

assets/parser.c.erb

@@ -669,7 +669,7 @@ typedef struct
 /** Parser shift table. */
 static const shift_t parser_shift_table[] = {
 <%   @parser.shift_table.each do |shift| %>
-    {<%= shift[:symbol_id] %>u, <%= shift[:state_id] %>u},
+    {<%= shift[:symbol].id %>u, <%= shift[:state_id] %>u},
 <%   end %>
 };
 

assets/parser.d.erb

@@ -817,7 +817,7 @@ private struct state_value_t
 /** Parser shift table. */
 private immutable shift_t[] parser_shift_table = [
 <%   @parser.shift_table.each do |shift| %>
-    shift_t(<%= shift[:symbol_id] %>u, <%= shift[:state_id] %>u),
+    shift_t(<%= shift[:symbol].id %>u, <%= shift[:state_id] %>u),
 <%   end %>
 ];
 

lib/propane/parser.rb

@@ -13,6 +13,7 @@ class Propane
       @log = log
       @item_sets = []
       @item_sets_set = {}
+      @sr_conflicts = Set.new
       start_item = Item.new(grammar.rules.first, 0)
       eval_item_sets = Set[ItemSet.new([start_item])]
 
@@ -38,8 +39,8 @@ class Propane
 
       build_reduce_actions!
       build_follow_sets!
-      write_log!
       build_tables!
+      write_log!
     end
 
     private
@@ -57,10 +58,17 @@ class Propane
               item_set.next_item_set[next_symbol].id
             end
           {
-            symbol_id: next_symbol.id,
+            symbol: next_symbol,
             state_id: state_id,
           }
         end
+        if item_set.reduce_actions
+          shift_entries.each do |shift_entry|
+            if item_set.reduce_actions.include?(shift_entry[:symbol])
+              @sr_conflicts << [shift_entry[:symbol], item_set.reduce_actions[shift_entry[:symbol]]]
+            end
+          end
+        end
         reduce_entries =
           if rule = item_set.reduce_rule
             [{token_id: @grammar.invalid_token_id, rule_id: rule.id, rule: rule,
@@ -310,6 +318,13 @@ class Propane
           end
         end
       end
+      if @sr_conflicts.size > 0
+        @log.puts
+        @log.puts "Shift/Reduce Conflicts:"
+        @sr_conflicts.each do |sr_conflict|
+          @log.puts "  Shift/Reduce conflict between #{sr_conflict[0].name} and #{sr_conflict[1].name}"
+        end
+      end
     end
 
   end

spec/propane_spec.rb

@@ -184,6 +184,20 @@ EOF
     expect(results.status).to_not eq 0
   end
 
+  it "warns on shift/reduce conflicts" do
+    write_grammar <<EOF
+token a;
+token b;
+Start -> As? b?;
+As -> a As2?;
+As2 -> b a As2?;
+EOF
+    results = run_propane(capture: true)
+    expect(results.stderr).to eq ""
+    expect(results.status).to eq 0
+    expect(File.binread("spec/run/testparser.log")).to match %r{Shift/Reduce conflict between b and As2}
+  end
+
   %w[d c].each do |language|
 
     context "#{language.upcase} language" do