Add error message support associated with definition rule

peglib.h

@@ -2735,6 +2735,12 @@ inline size_t Holder::parse_core(const char *s, size_t n, SemanticValues &vs,
           c.error_info.message = msg;
         }
       }
+    } else {
+      if (c.log && !outer_->error_message.empty() &&
+          c.error_info.message_pos < s) {
+        c.error_info.message_pos = s;
+        c.error_info.message = outer_->error_message;
+      }
     }
   });
 
@@ -3382,9 +3388,8 @@ private:
             opt(seq(g["InstructionItem"], zom(seq(g["InstructionItemSeparator"],
                                                   g["InstructionItem"])))),
             g["EndBlacket"]);
-    g["InstructionItem"] <= cho(g["PrecedenceClimbing"], g["ErrorMessage"],
+    g["InstructionItem"] <=
-                                g["NoAstOpt"]
+        cho(g["PrecedenceClimbing"], g["ErrorMessage"], g["NoAstOpt"]);
-                            );
     ~g["InstructionItemSeparator"] <= seq(chr(';'), g["Spacing"]);
 
     ~g["SpacesZom"] <= zom(g["Space"]);

test/test2.cc

@@ -2051,3 +2051,39 @@ SkipToRCUR ← (!RCUR (LCUR SkipToRCUR / .))* RCUR
 )",
             ast_to_s(ast));
 }
+
+TEST(ErrorTest, Error_message_with_rule_instruction) {
+  parser pg(R"(
+START       <- (LINE (ln LINE)*)? ln?
+
+LINE        <- STR '=' CODE
+
+CODE        <- HEX / DEC { message 'code format error...' }
+HEX         <- < [a-f0-9]+ 'h' >
+DEC         <- < [0-9]+ >
+
+STR         <- < [a-z0-9]+ >
+
+~ln         <- [\r\n]+
+%whitespace <- [ \t]*
+  )");
+
+  EXPECT_TRUE(!!pg);
+
+  std::vector<std::string> errors{
+      R"(2:5: code format error...)",
+  };
+
+  size_t i = 0;
+  pg.log = [&](size_t ln, size_t col, const std::string &msg) {
+    std::stringstream ss;
+    ss << ln << ":" << col << ": " << msg;
+    EXPECT_EQ(errors[i++], ss.str());
+  };
+
+  EXPECT_FALSE(pg.parse(R"(1 = ah
+2 = b
+3 = ch
+  )"));
+  EXPECT_EQ(i, errors.size());
+}