parse.y: Improve error reporting of type redef

It's happening regularly to me that I forget the type specifier when redef'ing
records or enums and usually it takes me a while to figure out what's going
on as the errors are not descriptive. Improve the error reporting and just
bail as there's no sensible way to continue.

Closes #2777

src/parse.y

@@ -1387,9 +1387,22 @@ decl:
 			build_global($2, $3, $4, $5, $6, VAR_CONST);
 			}
 
-	|	TOK_REDEF global_id opt_type init_class opt_init opt_attr ';'
+	|	TOK_REDEF global_id {
+			if ( $2->IsType() )
 				{
-			build_global($2, $3, $4, $5, $6, VAR_REDEF);
+				auto tag = $2->GetType()->Tag();
+				auto tstr = type_name(tag);
+				if ( tag == TYPE_RECORD || tag == TYPE_ENUM )
+					yyerror(zeek::util::fmt("redef of %s type %s is missing %s keyword",
+								tstr, $2->Name(), tstr));
+				else
+					yyerror(zeek::util::fmt("can not redef %s type %s", tstr, $2->Name()));
+
+				YYERROR;  // bail
+				}
+		} opt_type init_class opt_init opt_attr ';'
+			{
+			build_global($2, $4, $5, $6, $7, VAR_REDEF);
 			}
 
 	|	TOK_REDEF TOK_ENUM global_id TOK_ADD_TO '{'

testing/btest/Baseline/language.redef-missing-type-2/out

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/redef-missing-type.zeek, line 6: redef of enum type Color is missing enum keyword, at or near "Color"

testing/btest/Baseline/language.redef-missing-type-3/out

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/redef-missing-type.zeek, line 7: redef of enum type Color is missing enum keyword, at or near "Color"

testing/btest/Baseline/language.redef-missing-type-4/out

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/redef-missing-type.zeek, line 2: syntax error, at or near "count"

testing/btest/Baseline/language.redef-missing-type-5/out

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/redef-missing-type.zeek, line 2: can not redef table type string_set, at or near "string_set"

testing/btest/Baseline/language.redef-missing-type-6/out

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/redef-missing-type.zeek, line 3: can not redef vector type sv, at or near "sv"

testing/btest/Baseline/language.redef-missing-type/out

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/redef-missing-type.zeek, line 8: redef of record type MyRecord is missing record keyword, at or near "MyRecord"

testing/btest/language/redef-missing-type.zeek

@@ -0,0 +1,45 @@
+# @TEST-EXEC-FAIL: zeek -b %INPUT >out 2>&1
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff out
+
+type MyRecord: record {
+	s1: string;
+};
+
+redef MyRecord += {
+	s2: string;
+};
+
+
+# @TEST-START-NEXT
+type Color: enum {
+	RED,
+	GREEN,
+};
+
+redef Color += {
+	BLUE,
+};
+
+# @TEST-START-NEXT
+type Color: enum {
+	RED,
+	GREEN,
+};
+
+# This is very bogus.
+redef Color: enum += {
+	BLUE,
+};
+
+# @TEST-START-NEXT
+# ...more bogus things.
+redef count += { 1 };
+
+# @TEST-START-NEXT
+# ...more bogus things.
+redef string_set += { &log };
+
+# @TEST-START-NEXT
+# ...also bogus.
+type sv: vector of string;
+redef sv += { 1 };