0036 - 202x Feature Deprecations

• Planned Version: 202x
• Issues: #300, #291, #259, #135, LLVM #117715

Introduction

HLSL 2021 supports syntaxes and features that either do nothing, or are potentially confusing. This proposal tracks a set of minimal breaking changes for HLSL to remove misleading or confusing functionality.

Motivation

This proposal is part of a larger effort to reduce carried forward technical debt in HLSL compiler implementations.

Proposed solution

Removal of Effects Syntax

DXC supports parsing much of the legacy FXC effects syntax, however it emits warnings and does not provide any behavior associated with the effects syntax.

In HLSL 202x we should disable effects parsing support and allow those parsing failures to generate errors as would otherwise occur in HLSL.

Examples of effects syntax

< int foo=1; >
<
  string Name = "texa";
  int ArraySize = 3;
>;

sampler S : register(s1) = sampler_state {texture=tex;};
Texture2D l_tex { state=foo; };

int foobar2 {blah=foo;} = 5;

texture tex1 < int foo=1; > { state=foo; };


technique T0
{
  pass {}
}
Technique
{
  pass {}
}

int foobar5[] {1, 2, 3};
int foobar6[4] {1, 2, 3, 4};

Removal of interface Keyword

DXC supports interface declarations, however the semantic utility of interfaces is limited. Instances of interfaces cannot be created or passed around to functions. They can only be used as a static-verification that all required methods of an object are implemented.

Template-based polymorphic patterns available in HLSL 2021 and later enable many of the code patterns that interface declarations would have previously been used for and should be the supported path going forward.

Removal of uniform Keyword

In DXC the uniform keyword is parsed and ignored. This may lead users to believing it has some impact when it does not. We should remove it.

Disallow cbuffer initializers

DXC allows variables within a cbuffer to have initializer clauses. The initializer clauses are ignored, and DXC does not issue a diagnostic. In HLSL 202x initializer clauses on declarations placed into an implicit or explicit cbuffer declaration are illegal and will produce an error.