[wgsl-in] Use deterministic ordering for dependency ordering.

Use `FastIndexSet`, rather than `FastHashSet`, for tracking global
declarations' dependencies, so that the order in which functions are
inserted into the `Module` is not dependent on the hash function.

src/front/wgsl/parse/ast.rs

@@ -1,5 +1,5 @@
 use crate::front::wgsl::parse::number::Number;
-use crate::{Arena, FastHashSet, Handle, Span};
+use crate::{Arena, FastIndexSet, Handle, Span};
 use std::hash::Hash;
 
 #[derive(Debug, Default)]
@@ -73,7 +73,7 @@ pub struct GlobalDecl<'a> {
 
     /// Names of all module-scope or predeclared objects this
     /// declaration uses.
-    pub dependencies: FastHashSet<Dependency<'a>>,
+    pub dependencies: FastIndexSet<Dependency<'a>>,
 }
 
 #[derive(Debug)]

src/front/wgsl/parse/mod.rs

@@ -2,7 +2,7 @@ use crate::front::wgsl::error::{Error, ExpectedToken};
 use crate::front::wgsl::parse::lexer::{Lexer, Token};
 use crate::front::wgsl::parse::number::Number;
 use crate::front::SymbolTable;
-use crate::{Arena, FastHashSet, Handle, ShaderStage, Span};
+use crate::{Arena, FastIndexSet, Handle, ShaderStage, Span};
 
 pub mod ast;
 pub mod conv;
@@ -51,7 +51,7 @@ struct ExpressionContext<'input, 'temp, 'out> {
     ///
     /// [`GlobalDecl`]: ast::GlobalDecl
     /// [`dependencies`]: ast::GlobalDecl::dependencies
-    unresolved: &'out mut FastHashSet<ast::Dependency<'input>>,
+    unresolved: &'out mut FastIndexSet<ast::Dependency<'input>>,
 }
 
 impl<'a> ExpressionContext<'a, '_, '_> {
@@ -2076,7 +2076,7 @@ impl Parser {
         &mut self,
         lexer: &mut Lexer<'a>,
         out: &mut ast::TranslationUnit<'a>,
-        dependencies: &mut FastHashSet<ast::Dependency<'a>>,
+        dependencies: &mut FastIndexSet<ast::Dependency<'a>>,
     ) -> Result<ast::Function<'a>, Error<'a>> {
         self.push_rule_span(Rule::FunctionDecl, lexer);
         // read function name
@@ -2238,7 +2238,7 @@ impl Parser {
             (None, None) => {}
         }
 
-        let mut dependencies = FastHashSet::default();
+        let mut dependencies = FastIndexSet::default();
         let mut ctx = ExpressionContext {
             expressions: &mut out.expressions,
             local_table: &mut SymbolTable::default(),

tests/out/wgsl/module-scope.wgsl

@@ -9,14 +9,14 @@ var Texture: texture_2d<f32>;
 @group(0) @binding(1) 
 var Sampler: sampler;
 
-fn returns() -> S {
-    return S(Value);
-}
-
 fn statement() {
     return;
 }
 
+fn returns() -> S {
+    return S(Value);
+}
+
 fn call() {
     statement();
     let _e0 = returns();