wgsl: Replace [[decoration]] with @decoration

Deprecate the old syntax. Migrate everything to the new syntax.

Bug: tint:1382
Change-Id: Ide12b2e927b17dc93b9714c7049090864cc568d3
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/77260
Reviewed-by: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: David Neto <dneto@google.com>
Commit-Queue: David Neto <dneto@google.com>

docs/origin-trial-changes.md

@@ -11,7 +11,8 @@ Obviously infinite loops (no condition, no break) are now a validation error.
 The following features have been deprecated and will be removed in M102:
 
 * The `[[block]]` attribute has been deprecated. [tint:1324](https://crbug.com/tint/1324)
-* `elseif` has been replaced with `else if` [tint:1289](https://crbug.com/tint/1289)
+* Attributes now use the `@decoration` syntax instead of the `[[decoration]]` syntax. [tint:1382](https://crbug.com/tint/1382)
+* `elseif` has been replaced with `else if`. [tint:1289](https://crbug.com/tint/1289)
 
 ### New Features
 

docs/spirv-input-output-variables.md

@@ -85,8 +85,8 @@ through the copying and optimize the result.
 Current translation, through SPIR-V, SPIR-V reader, WGSL writer:
 
 ```groovy
-    [[location(0)]] var<out> frag_colour : vec4<f32>;
-    [[location(0)]] var<in> the_colour : vec4<f32>;
+    @location(0) var<out> frag_colour : vec4<f32>;
+    @location(0) var<in> the_colour : vec4<f32>;
 
     fn bar_() -> void {
       const x_14 : vec4<f32> = the_colour;
@@ -94,7 +94,7 @@ Current translation, through SPIR-V, SPIR-V reader, WGSL writer:
       return;
     }
 
-    [[stage(fragment)]]
+    @stage(fragment)
     fn main() -> void {
       bar_();
       return;
@@ -123,14 +123,14 @@ Proposed translation, through SPIR-V, SPIR-V reader, WGSL writer:
 
     // Declare a structure type to collect the return values.
     struct main_result_type {
-      [[location(0)]] frag_color : vec4<f32>;
+      @location(0) frag_color : vec4<f32>;
     };
 
-    [[stage(fragment)]]
+    @stage(fragment)
     fn main(
 
       // 'in' variables are entry point parameters
-      [[location(0)]] the_color_arg : vec4<f32>
+      @location(0) the_color_arg : vec4<f32>
 
     ) -> main_result_type {
 

docs/translations.md

@@ -188,4 +188,4 @@ static const <type> <name> = WGSL_SPEC_CONSTANT_<id>
 ```
 
 ## MSL
-`[[function_constant(<id>)]]`
+`@function_constant(<id>)`