From 82c1730db176a72a7efff222c68b9e38600035f8 Mon Sep 17 00:00:00 2001
From: Xaver Hugl <xaver.hugl@kde.org>
Date: Wed, 25 Jun 2025 15:39:46 +0200
Subject: [PATCH] scanner: warn on value 0 in bitfields

Sometimes they're used legitimately, but in some cases they're just nonsense.
For the legitimate use cases, this adds an optional "valid-zero" attribute
for bitfield entries, which can be used to suppress the warning.
---
 protocol/wayland.dtd |  1 +
 protocol/wayland.xml |  4 ++--
 src/scanner.c        | 12 ++++++++++++
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/protocol/wayland.dtd b/protocol/wayland.dtd
index b97372c5..62f4d778 100644
--- a/protocol/wayland.dtd
+++ b/protocol/wayland.dtd
@@ -24,6 +24,7 @@
   <!ATTLIST entry summary CDATA #IMPLIED>
   <!ATTLIST entry since CDATA #IMPLIED>
   <!ATTLIST entry deprecated-since CDATA #IMPLIED>
+  <!ATTLIST entry valid-zero CDATA #IMPLIED>
 <!ELEMENT arg (description?)>
   <!ATTLIST arg name CDATA #REQUIRED>
   <!ATTLIST arg type CDATA #REQUIRED>
diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index bee74a10..7802fbb9 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -1084,7 +1084,7 @@
 	or drags initiated with other buttons than BTN_LEFT to specific
 	actions (e.g. "ask").
       </description>
-      <entry name="none" value="0" summary="no action"/>
+      <entry name="none" value="0" summary="no action" valid-zero="true"/>
       <entry name="copy" value="1" summary="copy action"/>
       <entry name="move" value="2" summary="move action"/>
       <entry name="ask" value="4" summary="ask action"/>
@@ -1163,7 +1163,7 @@
 	use this information to adapt its behavior, e.g. choose
 	an appropriate cursor image.
       </description>
-      <entry name="none" value="0" summary="no edge"/>
+      <entry name="none" value="0" summary="no edge" valid-zero="true"/>
       <entry name="top" value="1" summary="top edge"/>
       <entry name="bottom" value="2" summary="bottom edge"/>
       <entry name="left" value="4" summary="left edge"/>
diff --git a/src/scanner.c b/src/scanner.c
index 1b71e60c..fa81c1f3 100644
--- a/src/scanner.c
+++ b/src/scanner.c
@@ -737,6 +737,7 @@ start_element(void *data, const char *element_name, const char **atts)
 	const char *enumeration_name = NULL;
 	const char *bitfield = NULL;
 	int i, version = 0;
+	bool valid_zero = false;
 
 	ctx->loc.line_number = XML_GetCurrentLineNumber(ctx->parser);
 	for (i = 0; atts[i]; i += 2) {
@@ -761,6 +762,14 @@ start_element(void *data, const char *element_name, const char **atts)
 			deprecated_since = atts[i + 1];
 		if (strcmp(atts[i], "allow-null") == 0)
 			allow_null = atts[i + 1];
+		if (strcmp(atts[i], "valid-zero") == 0) {
+			if (strcmp(atts[i + 1], "true") == 0)
+				valid_zero = true;
+			else
+				fail(&ctx->loc,
+				     "Invalid value for valid-zero: %s",
+				     atts[i + 1]);
+		}
 		if (strcmp(atts[i], "enum") == 0)
 			enumeration_name = atts[i + 1];
 		if (strcmp(atts[i], "bitfield") == 0)
@@ -914,6 +923,9 @@ start_element(void *data, const char *element_name, const char **atts)
 			     version, entry->since);
 		entry->deprecated_since = version;
 
+		if (ctx->enumeration->bitfield && !valid_zero && strcmp(entry->value, "0") == 0)
+			warn(&ctx->loc, "value 0 used in a bitfield entry");
+
 		if (summary)
 			entry->summary = xstrdup(summary);
 		else