feat(wgsl-in): create skeleton for parsing directives

CHANGELOG.md

@@ -85,6 +85,7 @@ By @bradwerth [#6216](https://github.com/gfx-rs/wgpu/pull/6216).
 - Support local `const` declarations in WGSL. By @sagudev in [#6156](https://github.com/gfx-rs/wgpu/pull/6156).
 - Implemented `const_assert` in WGSL. By @sagudev in [#6198](https://github.com/gfx-rs/wgpu/pull/6198).
 - Support polyfilling `inverse` in WGSL. By @chyyran in [#6385](https://github.com/gfx-rs/wgpu/pull/6385).
+- Add an internal skeleton for parsing `requires`, `enable`, and `diagnostic` directives that don't yet do anything besides emit nicer errors. By @ErichDonGubler in [#6352](https://github.com/gfx-rs/wgpu/pull/6352).
 
 #### General
 

Cargo.lock

@@ -1897,6 +1897,7 @@ dependencies = [
  "rustc-hash",
  "serde",
  "spirv 0.3.0+sdk-1.3.268.0",
+ "strum",
  "termcolor",
  "thiserror",
  "unicode-xid",

naga/Cargo.toml

@@ -101,3 +101,4 @@ ron = "0.8.0"
 rspirv = { version = "0.11", git = "https://github.com/gfx-rs/rspirv", rev = "b969f175d5663258b4891e44b76c1544da9661ab" }
 serde = { workspace = true, features = ["derive"] }
 spirv = { version = "0.3", features = ["deserialize"] }
+strum.workspace = true

naga/src/front/wgsl/error.rs

@@ -1,3 +1,4 @@
+use crate::front::wgsl::parse::directive::{DirectiveKind, UnimplementedDirectiveKind};
 use crate::front::wgsl::parse::lexer::Token;
 use crate::front::wgsl::Scalar;
 use crate::proc::{Alignment, ConstantEvaluatorError, ResolveError};
@@ -265,6 +266,13 @@ pub(crate) enum Error<'a> {
     PipelineConstantIDValue(Span),
     NotBool(Span),
     ConstAssertFailed(Span),
+    DirectiveNotYetImplemented {
+        kind: UnimplementedDirectiveKind,
+        span: Span,
+    },
+    DirectiveAfterFirstGlobalDecl {
+        directive_span: Span,
+    },
 }
 
 #[derive(Clone, Debug)]
@@ -861,6 +869,36 @@ impl<'a> Error<'a> {
                 labels: vec![(span, "evaluates to false".into())],
                 notes: vec![],
             },
+            Error::DirectiveNotYetImplemented { kind, span } => ParseError {
+                message: format!(
+                    "`{}` is not yet implemented",
+                    DirectiveKind::Unimplemented(kind).to_ident()
+                ),
+                labels: vec![(
+                    span,
+                    "this global directive is standard, but not yet implemented".into(),
+                )],
+                notes: vec![format!(
+                    concat!(
+                        "Let Naga maintainers know that you ran into this at ",
+                        "<https://github.com/gfx-rs/wgpu/issues/{}>, ",
+                        "so they can prioritize it!"
+                    ),
+                    kind.tracking_issue_num()
+                )],
+            },
+            Error::DirectiveAfterFirstGlobalDecl { directive_span } => ParseError {
+                message: "expected global declaration, but found a global directive".into(),
+                labels: vec![(
+                    directive_span,
+                    "written after first global declaration".into(),
+                )],
+                notes: vec![concat!(
+                    "global directives are only allowed before global declarations; ",
+                    "maybe hoist this closer to the top of the shader module?"
+                )
+                .into()],
+            },
         }
     }
 }

naga/src/front/wgsl/mod.rs

@@ -58,3 +58,21 @@ impl Frontend {
 pub fn parse_str(source: &str) -> Result<crate::Module, ParseError> {
     Frontend::new().parse(source)
 }
+
+#[cfg(test)]
+#[track_caller]
+pub fn assert_parse_err(input: &str, snapshot: &str) {
+    let output = parse_str(input)
+        .expect_err("expected parser error")
+        .emit_to_string(input);
+    if output != snapshot {
+        for diff in diff::lines(snapshot, &output) {
+            match diff {
+                diff::Result::Left(l) => println!("-{l}"),
+                diff::Result::Both(l, _) => println!(" {l}"),
+                diff::Result::Right(r) => println!("+{r}"),
+            }
+        }
+        panic!("Error snapshot failed");
+    }
+}

naga/src/front/wgsl/parse/directive.rs

@@ -0,0 +1,179 @@
+//! WGSL directives. The focal point of this API is [`DirectiveKind`].
+//!
+//! See also <https://www.w3.org/TR/WGSL/#directives>.
+
+/// A parsed sentinel word indicating the type of directive to be parsed next.
+#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
+pub enum DirectiveKind {
+    Unimplemented(UnimplementedDirectiveKind),
+}
+
+impl DirectiveKind {
+    const DIAGNOSTIC: &'static str = "diagnostic";
+    const ENABLE: &'static str = "enable";
+    const REQUIRES: &'static str = "requires";
+
+    /// Convert from a sentinel word in WGSL into its associated [`DirectiveKind`], if possible.
+    pub fn from_ident(s: &str) -> Option<Self> {
+        Some(match s {
+            Self::DIAGNOSTIC => Self::Unimplemented(UnimplementedDirectiveKind::Diagnostic),
+            Self::ENABLE => Self::Unimplemented(UnimplementedDirectiveKind::Enable),
+            Self::REQUIRES => Self::Unimplemented(UnimplementedDirectiveKind::Requires),
+            _ => return None,
+        })
+    }
+
+    /// Maps this [`DirectiveKind`] into the sentinel word associated with it in WGSL.
+    pub const fn to_ident(self) -> &'static str {
+        match self {
+            Self::Unimplemented(kind) => match kind {
+                UnimplementedDirectiveKind::Diagnostic => Self::DIAGNOSTIC,
+                UnimplementedDirectiveKind::Enable => Self::ENABLE,
+                UnimplementedDirectiveKind::Requires => Self::REQUIRES,
+            },
+        }
+    }
+
+    #[cfg(test)]
+    fn iter() -> impl Iterator<Item = Self> {
+        use strum::IntoEnumIterator;
+
+        UnimplementedDirectiveKind::iter().map(Self::Unimplemented)
+    }
+}
+
+/// A [`DirectiveKind`] that is not yet implemented. See [`DirectiveKind::Unimplemented`].
+#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
+#[cfg_attr(test, derive(strum::EnumIter))]
+pub enum UnimplementedDirectiveKind {
+    Diagnostic,
+    Enable,
+    Requires,
+}
+
+impl UnimplementedDirectiveKind {
+    pub const fn tracking_issue_num(self) -> u16 {
+        match self {
+            Self::Diagnostic => 5320,
+            Self::Requires => 6350,
+            Self::Enable => 5476,
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use strum::IntoEnumIterator;
+
+    use crate::front::wgsl::assert_parse_err;
+
+    use super::{DirectiveKind, UnimplementedDirectiveKind};
+
+    #[test]
+    fn unimplemented_directives() {
+        for unsupported_shader in UnimplementedDirectiveKind::iter() {
+            let shader;
+            let expected_msg;
+            match unsupported_shader {
+                UnimplementedDirectiveKind::Diagnostic => {
+                    shader = "diagnostic(off,derivative_uniformity);";
+                    expected_msg = "\
+error: `diagnostic` is not yet implemented
+  ┌─ wgsl:1:1
+  │
+1 │ diagnostic(off,derivative_uniformity);
+  │ ^^^^^^^^^^ this global directive is standard, but not yet implemented
+  │
+  = note: Let Naga maintainers know that you ran into this at <https://github.com/gfx-rs/wgpu/issues/5320>, so they can prioritize it!
+
+";
+                }
+                UnimplementedDirectiveKind::Enable => {
+                    shader = "enable f16;";
+                    expected_msg = "\
+error: `enable` is not yet implemented
+  ┌─ wgsl:1:1
+  │
+1 │ enable f16;
+  │ ^^^^^^ this global directive is standard, but not yet implemented
+  │
+  = note: Let Naga maintainers know that you ran into this at <https://github.com/gfx-rs/wgpu/issues/5476>, so they can prioritize it!
+
+";
+                }
+                UnimplementedDirectiveKind::Requires => {
+                    shader = "requires readonly_and_readwrite_storage_textures";
+                    expected_msg = "\
+error: `requires` is not yet implemented
+  ┌─ wgsl:1:1
+  │
+1 │ requires readonly_and_readwrite_storage_textures
+  │ ^^^^^^^^ this global directive is standard, but not yet implemented
+  │
+  = note: Let Naga maintainers know that you ran into this at <https://github.com/gfx-rs/wgpu/issues/6350>, so they can prioritize it!
+
+";
+                }
+            };
+
+            assert_parse_err(shader, expected_msg);
+        }
+    }
+
+    #[test]
+    fn directive_after_global_decl() {
+        for unsupported_shader in DirectiveKind::iter() {
+            let directive;
+            let expected_msg;
+            match unsupported_shader {
+                DirectiveKind::Unimplemented(UnimplementedDirectiveKind::Diagnostic) => {
+                    directive = "diagnostic(off,derivative_uniformity)";
+                    expected_msg = "\
+error: expected global declaration, but found a global directive
+  ┌─ wgsl:2:1
+  │
+2 │ diagnostic(off,derivative_uniformity);
+  │ ^^^^^^^^^^ written after first global declaration
+  │
+  = note: global directives are only allowed before global declarations; maybe hoist this closer to the top of the shader module?
+
+";
+                }
+                DirectiveKind::Unimplemented(UnimplementedDirectiveKind::Enable) => {
+                    directive = "enable f16";
+                    expected_msg = "\
+error: expected global declaration, but found a global directive
+  ┌─ wgsl:2:1
+  │
+2 │ enable f16;
+  │ ^^^^^^ written after first global declaration
+  │
+  = note: global directives are only allowed before global declarations; maybe hoist this closer to the top of the shader module?
+
+";
+                }
+                DirectiveKind::Unimplemented(UnimplementedDirectiveKind::Requires) => {
+                    directive = "requires readonly_and_readwrite_storage_textures";
+                    expected_msg = "\
+error: expected global declaration, but found a global directive
+  ┌─ wgsl:2:1
+  │
+2 │ requires readonly_and_readwrite_storage_textures;
+  │ ^^^^^^^^ written after first global declaration
+  │
+  = note: global directives are only allowed before global declarations; maybe hoist this closer to the top of the shader module?
+
+";
+                }
+            }
+
+            let shader = format!(
+                "\
+@group(0) @binding(0) var<storage> thing: i32;
+{directive};
+"
+            );
+            assert_parse_err(&shader, expected_msg);
+        }
+    }
+}

naga/src/front/wgsl/parse/lexer.rs

@@ -355,7 +355,6 @@ impl<'a> Lexer<'a> {
         }
     }
 
-    #[allow(dead_code)]
     pub(in crate::front::wgsl) fn peek_ident_with_span(
         &mut self,
     ) -> Result<(&'a str, Span), Error<'a>> {

naga/src/front/wgsl/parse/mod.rs

@@ -1,4 +1,5 @@
 use crate::front::wgsl::error::{Error, ExpectedToken};
+use crate::front::wgsl::parse::directive::DirectiveKind;
 use crate::front::wgsl::parse::lexer::{Lexer, Token};
 use crate::front::wgsl::parse::number::Number;
 use crate::front::wgsl::Scalar;
@@ -7,6 +8,7 @@ use crate::{Arena, FastIndexSet, Handle, ShaderStage, Span};
 
 pub mod ast;
 pub mod conv;
+pub mod directive;
 pub mod lexer;
 pub mod number;
 
@@ -136,6 +138,7 @@ enum Rule {
     SingularExpr,
     UnaryExpr,
     GeneralExpr,
+    Directive,
 }
 
 struct ParsedAttribute<T> {
@@ -2357,6 +2360,9 @@ impl Parser {
         let start = lexer.start_byte_offset();
         let kind = match lexer.next() {
             (Token::Separator(';'), _) => None,
+            (Token::Word(word), directive_span) if DirectiveKind::from_ident(word).is_some() => {
+                return Err(Error::DirectiveAfterFirstGlobalDecl { directive_span });
+            }
             (Token::Word("struct"), _) => {
                 let name = lexer.next_ident()?;
 
@@ -2474,6 +2480,24 @@ impl Parser {
 
         let mut lexer = Lexer::new(source);
         let mut tu = ast::TranslationUnit::default();
+
+        // Parse directives.
+        #[allow(clippy::never_loop, unreachable_code)]
+        while let Ok((ident, span)) = lexer.peek_ident_with_span() {
+            if let Some(kind) = DirectiveKind::from_ident(ident) {
+                self.push_rule_span(Rule::Directive, &mut lexer);
+                let _ = lexer.next_ident_with_span().unwrap();
+                match kind {
+                    DirectiveKind::Unimplemented(kind) => {
+                        return Err(Error::DirectiveNotYetImplemented { kind, span })
+                    }
+                }
+                self.pop_rule_span(&lexer);
+            } else {
+                break;
+            }
+        }
+
         loop {
             match self.global_decl(&mut lexer, &mut tu) {
                 Err(error) => return Err(error),