From 021ec4962bb7f539effbc325f2771b034fdf62bb Mon Sep 17 00:00:00 2001
From: Bill Currie <bill@taniwha.org>
Date: Sun, 24 Apr 2022 15:16:15 +0900
Subject: [PATCH] [cexpr] Add optional error message prefix string

The prefix gives more context to the error messages, making the system a
lot easier to use (it was especially helpful when getting my cvar revamp
into shape).
---
 include/QF/cexpr.h    |  1 +
 libs/util/cexpr-lex.l | 13 +++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/QF/cexpr.h b/include/QF/cexpr.h
index c0d608f80..91e19ced2 100644
--- a/include/QF/cexpr.h
+++ b/include/QF/cexpr.h
@@ -99,6 +99,7 @@ typedef struct exprctx_s {
 	exprval_t  *result;
 	exprtab_t  *symtab;				// directly accessible symbols
 	exprtab_t  *external_variables;	// accessible via $id
+	const char *msg_prefix;			// optional prefix for error messages
 	struct memsuper_s *memsuper;
 	const struct plitem_s *item;
 	struct plitem_s *messages;
diff --git a/libs/util/cexpr-lex.l b/libs/util/cexpr-lex.l
index bb4387a10..28551b1dc 100644
--- a/libs/util/cexpr-lex.l
+++ b/libs/util/cexpr-lex.l
@@ -94,9 +94,18 @@ cexpr_error(exprctx_t *ctx, const char *fmt, ...)
 	va_end (args);
 
 	if (ctx->messages) {
-		PL_Message (ctx->messages, ctx->item, "%s", string->str);
+		if (ctx->msg_prefix) {
+			PL_Message (ctx->messages, ctx->item, "%s:%s",
+						ctx->msg_prefix, string->str);
+		} else {
+			PL_Message (ctx->messages, ctx->item, "%s", string->str);
+		}
 	} else {
-		Sys_Printf ("%s\n", string->str);
+		if (ctx->msg_prefix) {
+			Sys_Printf ("%s:%s\n", ctx->msg_prefix, string->str);
+		} else {
+			Sys_Printf ("%s\n", string->str);
+		}
 	}
 	dstring_delete (string);
 }