0004 - 202x Feature Removals

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

Note: this proposal was introduced in Microsoft’s hlsl-specs as deprecations. In Ecma the proposal is categorized as removals, because the proposal is to not include these features in the first edition of the specification.

Implementation Status

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 mode, the effects parsing support should be disabled so that parsing failures generate errors as would otherwise occur in HLSL. Conformant compilers should not support parsing the effects syntax.

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.

Conforming implementations will not treat the interface keyword as a reserved word, and will not support any special parsing or semantic handling for interface declarations. Use of the interface keyword as a class-key in the grammar for specifying a declaration shall be rejected and produce a diagnostic.

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.

Conforming implementations will not treat the uniform keyword as a reserved word, and will not support any special parsing or semantic handling for variables with the uniform type attribute applied. Use of the uniform keyword as a keyword attribute on any declaration shall be rejected and produce a diagnostic.

Removal of shared Keyword

In DXC the shared 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.

Conforming implementations shall reject initializers on declarations inside cbuffer declarations and on declarations added to the implicit global cbuffer.