Replace <feature number> attribute with <feature depends>

Initially this PR only updates the XML schema and vk.xml.

The generator scripts will need to be modified to do a topological sort
on the dependencies, and downstream repositories such as validation
layers and Vulkan-Hpp will need to be updated to remove or replace their
usage of the old attribute.

registry.adoc

@@ -1,5 +1,4 @@
 // Copyright 2013-2024 The Khronos Group Inc.
-//
 // SPDX-License-Identifier: CC-BY-4.0
 
 // Core versions and extensions to enable
@@ -1293,10 +1292,32 @@ that API and version.
     Version name, used as the C preprocessor token under which the version's
     interfaces are protected against multiple inclusion.
     Example: `"VK_VERSION_1_0"`.
-  * attr:number - required.
-    Feature version number, usually a string interpreted as
-    `majorNumber.minorNumber`.
-    Example: `4.2`.
+  * attr:depends - optional.
+    String containing a boolean expression of one or more API core version
+    and extension names.
+    The feature requires the expression in the string to be satisfied to
+    use any functionality it defines.
+    Supported operators include `,` for logical OR, `+` for logical AND, and
+    `(` `)` for grouping.
+    `,` and `+` are of equal precedence, and lower than `(` `)`.
+    Expressions must be evaluated left-to-right for operators of the same
+    precedence.
+    Terms which are core version names are true if the corresponding
+    API version is supported.
+    Terms which are extension names are true if the corresponding extension
+    is enabled.
++
+--
+[NOTE]
+.Note
+====
+attr:depends replaces the attr:number attribute used in the past.
+The expected purposes of this attribute include sorting features in
+dependency order when emitting them from generator scripts, and ensuring
+that all dependent features are included when building with a specified
+feature.
+====
+--
   * attr:sortorder - optional.
     A decimal number which specifies an order relative to other tag:feature
     tags when calling output generators.
@@ -3049,6 +3070,8 @@ Changes to the `.xml` files and Python scripts are logged in GitHub history.
 [[changelog]]
 = Change Log
 
+  * 2024-03-20 - Replace the tag:feature attr:number tag with the
+    attr:depends tag (public issue 2327).
   * 2024-01-31 - Specify the meaning of the tag:member attr:len attribute of
     structure members when the member is a static array (internal issue
     3743).

xml/registry.rnc

@@ -406,7 +406,8 @@ Command = element command {
 #   api - API tag (e.g. 'gl', 'gles2', etc. - used internally, not
 #     necessarily an actual API name
 #   name - version name (C preprocessor name, e.g. GL_VERSION_4_2)
-#   number - version number, e.g. 4.2
+#   depends - boolean expression of API and/or extension names
+#       upon which this feature depends.
 #   protect - additional #ifdef symbol to place around the feature
 #   sortorder - order relative to other features, default 0
 #   <require> / <remove> contains features to require or remove in
@@ -416,7 +417,7 @@ Command = element command {
 Feature = element feature {
     attribute api { text } ,
     Name ,
-    attribute number { xsd:float } ,
+    attribute depends { text } ?,
     attribute protect { text } ? ,
     attribute sortorder { xsd:integer } ?,
     Comment ? ,

xml/vk.xml

@@ -15377,7 +15377,7 @@ typedef void* <name>MTLSharedEvent_id</name>;
         </command>
     </commands>
 
-    <feature api="vulkan,vulkansc" name="VK_VERSION_1_0" number="1.0" comment="Vulkan core API interface definitions">
+    <feature api="vulkan,vulkansc" name="VK_VERSION_1_0" comment="Vulkan core API interface definitions">
         <require comment="Header boilerplate">
             <type name="vk_platform"/>
             <type name="VK_DEFINE_HANDLE"/>
@@ -15892,7 +15892,7 @@ typedef void* <name>MTLSharedEvent_id</name>;
             <command name="vkCmdExecuteCommands"/>
         </require>
     </feature>
-    <feature api="vulkan,vulkansc" name="VK_VERSION_1_1" number="1.1" comment="Vulkan 1.1 core API interface definitions.">
+    <feature api="vulkan,vulkansc" name="VK_VERSION_1_1" depends="VK_VERSION_1_1" comment="Vulkan 1.1 core API interface definitions.">
         <require>
             <type name="VK_API_VERSION_1_1"/>
         </require>
@@ -16224,7 +16224,7 @@ typedef void* <name>MTLSharedEvent_id</name>;
             <type name="VkPhysicalDeviceShaderDrawParametersFeatures"/>
         </require>
     </feature>
-    <feature api="vulkan,vulkansc" name="VK_VERSION_1_2" number="1.2" comment="Vulkan 1.2 core API interface definitions.">
+    <feature api="vulkan,vulkansc" name="VK_VERSION_1_2" depends="VK_VERSION_1_2" comment="Vulkan 1.2 core API interface definitions.">
         <require>
             <type name="VK_API_VERSION_1_2"/>
         </require>
@@ -16419,7 +16419,7 @@ typedef void* <name>MTLSharedEvent_id</name>;
             <command name="vkGetDeviceMemoryOpaqueCaptureAddress"/>
         </require>
     </feature>
-    <feature api="vulkan,vulkansc" name="VK_VERSION_1_3" number="1.3" comment="Vulkan 1.3 core API interface definitions.">
+    <feature api="vulkan,vulkansc" name="VK_VERSION_1_3" depends="VK_VERSION_1_3" comment="Vulkan 1.3 core API interface definitions.">
         <require>
             <type name="VK_API_VERSION_1_3"/>
         </require>
@@ -16684,7 +16684,7 @@ typedef void* <name>MTLSharedEvent_id</name>;
         </require>
     </feature>
 
-    <feature api="vulkansc" name="VKSC_VERSION_1_0" number="1.0" comment="Vulkan SC core API interface definitions">
+    <feature api="vulkansc" name="VKSC_VERSION_1_0" depends="VK_VERSION_1_2" comment="Vulkan SC core API interface definitions">
         <require>
             <type name="VKSC_API_VARIANT"/>
             <type name="VKSC_API_VERSION_1_0"/>