WGSL preprocess and composer utilities aligned with naga_oil.

wgsl

shader

Author

Milky2018

Version

0.6.2

License

Apache-2.0

Repository

github.com/moonbit-community/moon_wgsl

Last updated

5 months ago

Downloads

393

#moon_wgsl

Milky2018/moon_wgsl is a MoonBit library for WGSL preprocessing, import analysis, and shader composition.

The public surface follows naga_oil concepts while staying source-level and multi-backend. Import the focused subpackage you need, such as @common, @ast, @parser, @metadata, @preprocess, @resolver, @analysis, @import_planner, @virtual_overrides, @writeback, @compose, or @export:

///|
test "README: common package surface" {
  let value_defines = @common.default_wgsl_value_defines()
  debug_inspect(value_defines.length() > 0, content="true")
}

#What This Library Provides

moon_wgsl focuses on three related tasks:

Parse shader metadata such as #define_import_path, #define, used imports, and top-level WGSL directives.
Preprocess shader source with conditional compilation and shader-definition substitution.
Compose WGSL modules by resolving #import directives from a registered in-memory source registry.

The library is intended for projects that want naga_oil-style shader module composition in MoonBit without introducing a separate CLI step.

#Highlights

Supports #ifdef, #ifndef, #if, #else if, #else, and #endif.
Supports shader definition values of type Bool, Int, and UInt.
Parses grouped imports such as #import bevy_render::{view::View, maths::{PI_2, powsafe}}.
Supports import aliases such as #import bevy_render::maths as maths.
Supports quoted file-path imports such as #import "../shared/common.wgsl" SharedVertex, build_color.
Supports bulk source registration with register_source_files.
Supports source-tree scanning and registration through moonbitlang/x/fs.
Supports preflight registry diagnostics with analyze_source_files and register_source_files_checked.
Preserves and re-emits WGSL enable, requires, and diagnostic(...) directives.
Tracks only actually used imported items when extracting metadata.
Resolves composable modules from registered WGSL source strings.
Exports single-file WGSL with declaration-level tree-shaking, an explicit source catalog, source-map entries, and diagnostics.
Supports token-based source-level symbol redirects during composition and export.

#Core Concepts

#1. Metadata Extraction

Use @metadata.get_preprocessor_metadata when you want to inspect a shader without fully composing it.

Metadata includes:

Optional module name from #define_import_path
Imported module/item pairs that are actually used
Module-local shader definitions declared with #define
Effective definition names referenced by conditional blocks or #NAME substitutions
Top-level WGSL directives

Example:

///|
test "README: metadata extraction" {
  let metadata : @common.PreprocessorMetaData = @metadata.get_preprocessor_metadata(
    "#define_import_path bevy_ui::ui_node\n#define HDR\n#define TONEMAP_MODE 2\n#import bevy_render::{view::View, globals::Globals}\n#import bevy_render::maths as maths\nfn main(view: View, globals: Globals) -> f32 {\n  return maths::tone_map(1.0);\n}\n",
  ) catch {
    _ => abort("expected metadata extraction success")
  }

  debug_inspect(metadata.name, content="Some(\"bevy_ui::ui_node\")")
  debug_inspect(metadata.imports.length(), content="3")
  debug_inspect(metadata.wgsl_directives.is_empty(), content="true")
}

#2. Preprocessing a Single Shader

Use Preprocessor::preprocess to evaluate conditional blocks, strip import declarations from the output, and substitute shader-definition values.

///|
test "README: preprocess single shader" {
  let defs : @hashmap.HashMap[String, @common.ShaderDefValue] = @hashmap.HashMap::new()
  defs.set("TEXTURE", @common.ShaderDefValue::Bool(true))

  let source = "#ifdef TEXTURE\nvar sprite_texture: texture_2d<f32>;\n#else\nvar sprite_texture: texture_2d_array<f32>;\n#endif\n"

  let output : @common.PreprocessOutput = @preprocess.Preprocessor::default().preprocess(
    source, defs,
  ) catch {
    _ => abort("preprocess failed")
  }

  debug_inspect(
    output.preprocessed_source.contains("texture_2d<f32>"),
    content="true",
  )
  debug_inspect(output.imports.length(), content="0")
}

#3. Composing Registered WGSL Modules

Composer expands #import directives recursively, resolves aliases, and merges imported definitions into a final WGSL string.

The recommended path is to register shaders on the Composer instance itself. Composer::default() starts with an empty registry and owns all state needed for module resolution and composition.

///|
test "README: compose registered modules" {
  let composer : @compose.Composer = @compose.Composer::default()
  let defines : @hashmap.HashMap[String, Bool] = @hashmap.HashMap::new()
  let redirects : Array[@common.WgslSymbolRedirect] = []
  composer.clear_sources()

  composer.register_source(
    "render/maths.wgsl", "#define_import_path bevy_render::maths\nconst PI_2: f32 = 6.28318;\n",
  )

  composer.register_source(
    "sprite_render/mesh2d/mesh2d_functions.wgsl", "#define_import_path bevy_sprite::mesh2d_functions\n#import bevy_render::maths::PI_2\nfn twice_pi() -> f32 {\n  return PI_2;\n}\n",
  )

  composer.register_source(
    "sprite_render/mesh2d/mesh2d.wgsl", "#import bevy_sprite::mesh2d_functions as mesh_functions\nfn demo() -> f32 {\n  return mesh_functions::twice_pi();\n}\n",
  )

  let compose_options : @common.WgslComposeOptions = {
    defines,
    value_defines: @common.default_wgsl_value_defines(),
    redirects,
    additional_imports: [],
  }
  let composed : String = composer.compose_wgsl(
    "sprite_render/mesh2d/mesh2d.wgsl", compose_options,
  ) catch {
    _ => abort("compose failed")
  }

  debug_inspect(composed.contains("fn demo"), content="true")
  debug_inspect(composed.contains("mesh_functions::"), content="false")
}

#4. Bulk Registry and Relative File Imports

You can register a batch of shader files at once and use relative quoted paths between them. Composer instances own the registry used by composition.

///|
test "README: bulk registry and relative imports" {
  let composer : @compose.Composer = @compose.Composer::default()
  let defines : @hashmap.HashMap[String, Bool] = @hashmap.HashMap::new()
  let redirects : Array[@common.WgslSymbolRedirect] = []
  let files : Array[@common.WgslSourceFile] = [
    {
      rel_path: "shaders/shared/common.wgsl",
      source: "struct SharedValue {\n  tint: vec4<f32>,\n}\n",
    },
    {
      rel_path: "shaders/effects/main.wgsl",
      source: "#import \"../shared/common.wgsl\" SharedValue\nfn shade(value: SharedValue) -> vec4<f32> {\n  return value.tint;\n}\n",
    },
  ]

  composer.clear_sources()
  composer.register_source_files(files)

  debug_inspect(
    composer.registered_source("shaders/effects/main.wgsl") is Some(_),
    content="true",
  )
  let compose_options : @common.WgslComposeOptions = {
    defines,
    value_defines: @common.default_wgsl_value_defines(),
    redirects,
    additional_imports: [],
  }
  let composed : String = composer.compose_wgsl(
    "shaders/effects/main.wgsl", compose_options,
  ) catch {
    _ => abort("compose failed")
  }
  debug_inspect(composed.contains("struct SharedValue"), content="true")
}

If you want collision diagnostics before mutating the registry, use the checked path:

///|
test "README: checked bulk registry" {
  let files : Array[@common.WgslSourceFile] = [
    {
      rel_path: "shaders/demo/a.wgsl",
      source: "#define_import_path demo::dup\nfn a() -> f32 { return 1.0; }\n",
    },
    {
      rel_path: "shaders/demo/b.wgsl",
      source: "#define_import_path demo::dup\nfn b() -> f32 { return 2.0; }\n",
    },
  ]

  let registry = @resolver.WgslSourceRegistry::default()
  let diagnostics : Array[@common.WgslDiagnostic] = registry.analyze_source_files(
    files,
  )
  debug_inspect(diagnostics.length(), content="1")

  let checked_diagnostics : Array[@common.WgslDiagnostic] = []
  registry.register_source_files_checked(files, checked_diagnostics)
  debug_inspect(checked_diagnostics.length(), content="1")
}

#5. Scanning a WGSL Source Tree

If your shaders already live on disk, use scan_wgsl_source_files or the Composer convenience helpers built on top of moonbitlang/x/fs.

Scanned rel_path values are relative to the scan root, so scanning assets/shaders yields registry keys such as effects/main.wgsl.

///|
test "README: scan source tree" {
  let composer : @compose.Composer = @compose.Composer::default()
  let defines : @hashmap.HashMap[String, Bool] = @hashmap.HashMap::new()
  let redirects : Array[@common.WgslSymbolRedirect] = []
  let scan_options : @common.WgslSourceScanOptions = {
    recursive: true,
    extensions: [".wgsl"],
    exclude_prefixes: ["ignored"],
  }

  composer.clear_sources()
  composer.register_source_tree("testdata/wgsl_scan", scan_options) catch {
    _ => abort("failed to scan WGSL shader tree")
  }

  let compose_options : @common.WgslComposeOptions = {
    defines,
    value_defines: @common.default_wgsl_value_defines(),
    redirects,
    additional_imports: [],
  }
  let composed : String = composer.compose_wgsl(
    "effects/main.wgsl", compose_options,
  ) catch {
    _ => abort("compose failed")
  }

  debug_inspect(composed.contains("fn shade"), content="true")
}

If you want to preflight a tree before registration, use the checked scan path:

///|
test "README: checked tree scan" {
  let (files, diagnostics) = @resolver.scan_wgsl_source_files_checked(
    "testdata/wgsl_scan_dups",
    @common.WgslSourceScanOptions::default(),
  ) catch {
    _ => abort("failed to scan WGSL shader tree")
  }

  debug_inspect(files.length(), content="2")
  debug_inspect(diagnostics.length(), content="1")
}

#6. Exporting a Single WGSL File

Use export_wgsl_with_options to produce a fully expanded single-file WGSL output. The export path also supports declaration-level tree-shaking and returns source-map entries, the dependency-closure source catalog used for matching, plus diagnostics.

///|
test "README: export single WGSL file" {
  let composer : @compose.Composer = @compose.Composer::default()
  let defines : @hashmap.HashMap[String, Bool] = @hashmap.HashMap::new()
  let redirects : Array[@common.WgslSymbolRedirect] = []
  let files : Array[@common.WgslSourceFile] = [
    {
      rel_path: "shaders/shared/common.wgsl",
      source: "struct SharedParams {\n  tint: vec4<f32>,\n}\nstruct SharedVertex {\n  params: SharedParams,\n}\nfn build_color(vertex: SharedVertex) -> vec4<f32> {\n  return vertex.params.tint;\n}\n",
    },
    {
      rel_path: "shaders/effects/main.wgsl",
      source: "#import \"../shared/common.wgsl\" SharedVertex, build_color\nfn shade(vertex: SharedVertex) -> vec4<f32> {\n  return build_color(vertex);\n}\n",
    },
  ]

  composer.clear_sources()
  composer.register_source_files(files)

  let compose_options : @common.WgslComposeOptions = {
    defines,
    value_defines: @common.default_wgsl_value_defines(),
    redirects,
    additional_imports: [],
  }
  let export_options : @common.WgslExportOptions = { root_items: ["shade"] }
  let exported : @common.WgslExportOutput = @export.export_wgsl_with_options(
    composer, "shaders/effects/main.wgsl", compose_options, export_options,
  ) catch {
    _ => abort("export failed")
  }

  debug_inspect(exported.source.contains("#import"), content="false")
  debug_inspect(exported.source_catalog.length() > 0, content="true")
  debug_inspect(exported.source_map.length() > 0, content="true")
  debug_inspect(exported.diagnostics.length(), content="0")
}

If you need the declaration catalog directly, without exporting a specific entrypoint, use build_wgsl_source_catalog on the same Composer:

///|
test "README: build source catalog" {
  let composer : @compose.Composer = @compose.Composer::default()
  let defines : @hashmap.HashMap[String, Bool] = @hashmap.HashMap::new()
  let redirects : Array[@common.WgslSymbolRedirect] = []
  let files : Array[@common.WgslSourceFile] = [
    {
      rel_path: "shaders/shared/common.wgsl",
      source: "struct SharedParams {\n  tint: vec4<f32>,\n}\nstruct SharedVertex {\n  params: SharedParams,\n}\nfn build_color(vertex: SharedVertex) -> vec4<f32> {\n  return vertex.params.tint;\n}\n",
    },
    {
      rel_path: "shaders/effects/main.wgsl",
      source: "#import \"../shared/common.wgsl\" SharedVertex, build_color\nfn shade(vertex: SharedVertex) -> vec4<f32> {\n  return build_color(vertex);\n}\n",
    },
  ]

  composer.clear_sources()
  composer.register_source_files(files)

  let compose_options : @common.WgslComposeOptions = {
    defines,
    value_defines: @common.default_wgsl_value_defines(),
    redirects,
    additional_imports: [],
  }
  let prepared = composer.prepare_wgsl_source(
    "shaders/effects/main.wgsl", compose_options,
  ) catch {
    err => abort("expected prepare success: \{err.message()}")
  }
  let catalog : Array[@common.WgslSourceCatalogEntry] = prepared.source_catalog
  debug_inspect(catalog.length() > 0, content="true")
}

#7. Applying Source-Level Redirects

Use the redirect-aware APIs when you want to remap one imported symbol to another during composition/export without depending on Naga IR.

///|
test "README: source-level redirects" {
  let composer : @compose.Composer = @compose.Composer::default()
  let defines : @hashmap.HashMap[String, Bool] = @hashmap.HashMap::new()
  let redirects : Array[@common.WgslSymbolRedirect] = [
    { from_name: "build_shadow", to_name: "build_color" },
  ]
  let files : Array[@common.WgslSourceFile] = [
    {
      rel_path: "shaders/shared/common.wgsl",
      source: "struct SharedParams {\n  tint: vec4<f32>,\n}\nstruct SharedVertex {\n  params: SharedParams,\n}\nfn build_color(vertex: SharedVertex) -> vec4<f32> {\n  return vertex.params.tint;\n}\nfn build_shadow(vertex: SharedVertex) -> vec4<f32> {\n  return vec4<f32>(0.0, 0.0, 0.0, 1.0);\n}\n",
    },
    {
      rel_path: "shaders/effects/redirect.wgsl",
      source: "#import \"../shared/common.wgsl\" SharedVertex, build_color, build_shadow\nfn shade(vertex: SharedVertex) -> vec4<f32> {\n  return build_shadow(vertex);\n}\n",
    },
  ]

  composer.clear_sources()
  composer.register_source_files(files)

  let compose_options : @common.WgslComposeOptions = {
    defines,
    value_defines: @common.default_wgsl_value_defines(),
    redirects,
    additional_imports: [],
  }
  let export_options : @common.WgslExportOptions = { root_items: ["shade"] }
  let exported : @common.WgslExportOutput = @export.export_wgsl_with_options(
    composer, "shaders/effects/redirect.wgsl", compose_options, export_options,
  ) catch {
    _ => abort("redirect export failed")
  }

  debug_inspect(exported.source.contains("build_shadow"), content="false")
  debug_inspect(exported.source.contains("build_color"), content="true")
}

#Import Syntax Supported

The parser supports several common import forms:

#import bevy_render::view::View
#import bevy_render::maths as maths
#import bevy_render::{view::View, globals::Globals}
#import bevy_render::{maths::{PI_2, powsafe}}
#import "shaders/skills/shared.wgsl" Vertex, VertexOutput
#import "../shared/common.wgsl" SharedVertex, build_color

#Public API Overview

Main public entry points:

Preprocessor Parses and preprocesses a single shader source string.
Composer Owns a WGSL registry and recursively composes registered shader modules.
@metadata.get_preprocessor_metadata Returns a rich metadata object for a shader source string.
WgslSourceRegistry::register_source / WgslSourceRegistry::registered_source Manage an explicit WGSL source registry value.
Composer::register_source / Composer::register_source_files Manage a Composer-owned WGSL source registry for hermetic composition.
Composer::compose_wgsl Composes WGSL from Composer-owned registry state and WgslComposeOptions.
WgslSourceRegistry::register_source_files Registers a batch of WGSL source files into an explicit registry.
WgslSourceRegistry::analyze_source_files Performs preflight validation for duplicate module names and rel-path ownership conflicts.
WgslSourceRegistry::register_source_files_checked Runs preflight registry diagnostics and only mutates registry state when no errors are reported.
build_wgsl_source_catalog Returns the declaration catalog for a prepared dependency closure.
WgslSourceRegistry::copy_import_module_paths / resolve_wgsl_import_module_in_registry Build and query module-path resolution data for an explicit registry.
resolve_wgsl_import_file_path_from_registry Resolves relative or quoted file-path imports against a source file path.
rewrite_wgsl_symbol_redirects Applies token-based source-level symbol redirects to WGSL source from the analysis package.
Composer::compose_wgsl_source Composes a raw WGSL source string using WgslComposeOptions without exposing session internals.
Composer::prepare_wgsl_source Produces a stable PreparedWgslSource intermediate for tools such as single-file export.
export_wgsl_with_options Produces single-file WGSL from WgslComposeOptions without depending on compose session internals.

Important public data structures:

ShaderDefValue
ImportDefinition
PreprocessOutput
PreprocessorMetaData
PreparedWgslSource
ComposableModuleDescriptor
ComposableModuleDefinition
WgslDirectives
WgslSourceFile
WgslComposeOptions Holds root compose settings: shader defs, value defs, symbol redirects, and root-only additional_imports.
WgslSymbolRedirect
WgslExportOptions
WgslExportOutput
WgslSourceCatalogEntry
WgslSourceMapEntry
WgslDiagnostic

For the full exported surface, see the generated subpackage interfaces: common/pkg.generated.mbti, ast/pkg.generated.mbti, parser/pkg.generated.mbti, metadata/pkg.generated.mbti, preprocess/pkg.generated.mbti, resolver/pkg.generated.mbti, analysis/pkg.generated.mbti, import_planner/pkg.generated.mbti, virtual_overrides/pkg.generated.mbti, writeback/pkg.generated.mbti, compose/pkg.generated.mbti, and export/pkg.generated.mbti.

#Behavior Notes

#define_import_path is used as the canonical module name for composition.
Composer now owns registry/module resolution state; new code should prefer Composer::register_source*, Composer::compose_wgsl, Composer::compose_wgsl_source, and export_wgsl_with_options.
Composer::default() is hermetic and starts with an empty registry.
Relative quoted file imports are resolved against the importing shader's registered path in the active Composer registry.
register_source_files_checked is the safe bulk-registration path when callers need deterministic diagnostics before mutating a Composer registry.
@metadata.get_preprocessor_metadata is strict like upstream naga_oil and raises MetadataError when directive or import metadata is invalid.
Preprocessor::preprocess is the strict path and raises PreprocessError when parsing or conditional evaluation fails.
export_wgsl_with_options scopes source_catalog and source_map to the dependency closure of the current compose/export preparation result instead of the full registry.
Source-level redirects are token-based and intentionally skip declaration heads, field accesses (.), and attributes (@...); they are intended for imported helper/type names rather than locally shadowed identifiers.

#Development

Run the test suite from the module root:

moon test

The repository currently includes tests for:

metadata extraction
grouped and aliased imports
quoted relative file imports
bulk registry collision diagnostics
source catalog exposure for ambiguous source-map diagnostics
WGSL directive preservation
conditional preprocessing semantics
module registration and import resolution
recursive composition behavior
source-level symbol redirects during composition/export
single-file WGSL export with tree-shaking and diagnostics

#Compatibility Goal

This package aims to preserve the practical naga_oil programming model used by existing downstream shader pipelines. The tests intentionally exercise behavior that matches upstream usage patterns from the original extraction context.

#License

Apache-2.0

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