feat: tgpu.fn(callback) for providing slots and accessors

packages/typegpu/src/core/function/tgpuFn.ts

@@ -41,6 +41,7 @@ import type {
   InheritArgNames,
 } from './fnTypes.ts';
 import { stripTemplate } from './templateUtils.ts';
+import type { TgpuBufferShorthand } from '../buffer/bufferShorthand.ts';
 
 // ----------
 // Public API
@@ -108,6 +109,28 @@ export type TgpuFn<ImplSchema extends AnyFn = (...args: any[]) => any> =
       };
   };
 
+/**
+ * A function wrapper that allows providing slot and accessor overrides for shellless functions
+ */
+export interface TgpuGenericFn<Callback extends AnyFn> {
+  readonly [$internal]: true;
+  readonly [$providing]?: Providing | undefined;
+  readonly resourceType: 'generic-function';
+  readonly callback: Callback;
+
+  with<T>(slot: TgpuSlot<T>, value: Eventual<T>): TgpuGenericFn<Callback>;
+  with<T extends AnyData>(
+    accessor: TgpuAccessor<T>,
+    value:
+      | TgpuFn<() => T>
+      | TgpuBufferUsage<T>
+      | TgpuBufferShorthand<T>
+      | Infer<T>,
+  ): TgpuGenericFn<Callback>;
+
+  (...args: Parameters<Callback>): ReturnType<Callback>;
+}
+
 export function fn<
   Args extends AnyData[] | [],
 >(argTypes: Args, returnType?: undefined): TgpuFnShell<Args, Void>;
@@ -117,10 +140,22 @@ export function fn<
   Return extends AnyData,
 >(argTypes: Args, returnType: Return): TgpuFnShell<Args, Return>;
 
+export function fn<Callback extends AnyFn>(
+  callback: Callback,
+): TgpuGenericFn<Callback>;
+
 export function fn<
   Args extends AnyData[] | [],
   Return extends AnyData = Void,
->(argTypes: Args, returnType?: Return | undefined): TgpuFnShell<Args, Return> {
+>(
+  argTypesOrCallback: Args | AnyFn,
+  returnType?: Return | undefined,
+): TgpuFnShell<Args, Return> | TgpuGenericFn<AnyFn> {
+  if (typeof argTypesOrCallback === 'function') {
+    return createGenericFn(argTypesOrCallback, []);
+  }
+
+  const argTypes = argTypesOrCallback;
   const shell: TgpuFnShellHeader<Args, Return> = {
     [$internal]: true,
     argTypes,
@@ -147,6 +182,13 @@ export function isTgpuFn<Args extends AnyData[] | [], Return extends AnyData>(
     (value as TgpuFn<(...args: Args) => Return>)?.resourceType === 'function';
 }
 
+export function isGenericFn<Callback extends AnyFn>(
+  value: unknown | TgpuGenericFn<Callback>,
+): value is TgpuGenericFn<Callback> {
+  return isMarkedInternal(value) &&
+    (value as TgpuGenericFn<Callback>)?.resourceType === 'generic-function';
+}
+
 // --------------
 // Implementation
 // --------------
@@ -328,3 +370,50 @@ function createBoundFunction<ImplSchema extends AnyFn>(
 
   return fn;
 }
+
+function createGenericFn<Callback extends AnyFn>(
+  callback: Callback,
+  pairs: SlotValuePair[],
+): TgpuGenericFn<Callback> {
+  type This = TgpuGenericFn<Callback>;
+
+  const fnBase = {
+    [$internal]: true as const,
+    resourceType: 'generic-function' as const,
+    callback,
+    [$providing]: pairs.length > 0
+      ? {
+        inner: callback,
+        pairs,
+      }
+      : undefined,
+
+    with(
+      slot: TgpuSlot<unknown> | TgpuAccessor,
+      value: unknown,
+    ): TgpuGenericFn<Callback> {
+      return createGenericFn(callback, [
+        ...pairs,
+        [isAccessor(slot) ? slot.slot : slot, value],
+      ]);
+    },
+  };
+
+  const call = ((...args: Parameters<Callback>): ReturnType<Callback> => {
+    return callback(...args) as ReturnType<Callback>;
+  }) as Callback;
+
+  const genericFn = Object.assign(call, fnBase) as unknown as This;
+
+  Object.defineProperty(genericFn, 'toString', {
+    value() {
+      const fnLabel = getName(callback) ?? '<unnamed>';
+      if (pairs.length > 0) {
+        return `fn*:${fnLabel}[${pairs.map(stringifyPair).join(', ')}]`;
+      }
+      return `fn*:${fnLabel}`;
+    },
+  });
+
+  return genericFn;
+}

packages/typegpu/src/index.ts

@@ -174,7 +174,11 @@ export type {
   TgpuLayoutTexture,
   TgpuLayoutUniform,
 } from './tgpuBindGroupLayout.ts';
-export type { TgpuFn, TgpuFnShell } from './core/function/tgpuFn.ts';
+export type {
+  TgpuFn,
+  TgpuFnShell,
+  TgpuGenericFn,
+} from './core/function/tgpuFn.ts';
 export type { TgpuComptime } from './core/function/comptime.ts';
 export type {
   TgpuVertexFn,

packages/typegpu/src/resolutionCtx.ts

@@ -607,6 +607,10 @@ export class ResolutionCtxImpl implements ResolutionCtx {
   }
 
   withSlots<T>(pairs: SlotValuePair<unknown>[], callback: () => T): T {
+    if (pairs.length === 0) {
+      return callback();
+    }
+
     this._itemStateStack.pushSlotBindings(pairs);
 
     try {

packages/typegpu/src/tgsl/wgslGenerator.ts

@@ -23,7 +23,7 @@ import { invariant, ResolutionError, WgslTypeError } from '../errors.ts';
 import { getName } from '../shared/meta.ts';
 import { isMarkedInternal } from '../shared/symbols.ts';
 import { safeStringify } from '../shared/stringify.ts';
-import { $internal } from '../shared/symbols.ts';
+import { $internal, $providing } from '../shared/symbols.ts';
 import { pow } from '../std/numeric.ts';
 import { add, div, mul, neg, sub } from '../std/operators.ts';
 import { type FnArgsConversionHint, isKnownAtComptime } from '../types.ts';
@@ -44,6 +44,8 @@ import type { DualFn } from '../data/dualFn.ts';
 import { createPtrFromOrigin, implicitFrom, ptrFn } from '../data/ptr.ts';
 import { RefOperator } from '../data/ref.ts';
 import { constant } from '../core/constant/tgpuConstant.ts';
+import { isGenericFn } from '../core/function/tgpuFn.ts';
+import type { SlotValuePair } from '../core/slot/slotTypes.ts';
 
 const { NodeTypeCatalog: NODE } = tinyest;
 
@@ -549,26 +551,44 @@ ${this.ctx.pre}}`;
         return callee.value.operator(callee.value.lhs, rhs);
       }
 
-      if (!isMarkedInternal(callee.value)) {
-        const args = argNodes.map((arg) => this.expression(arg));
-        const shellless = this.ctx.shelllessRepo.get(
-          callee.value as (...args: never[]) => unknown,
-          args,
+      if (!isMarkedInternal(callee.value) || isGenericFn(callee.value)) {
+        const slotPairs: SlotValuePair[] = isGenericFn(callee.value)
+          ? (callee.value[$providing]?.pairs ?? [])
+          : [];
+        const callback = isGenericFn(callee.value)
+          ? callee.value.callback
+          : (callee.value as (...args: never[]) => unknown);
+
+        const shelllessCall = this.ctx.withSlots(
+          slotPairs,
+          (): Snippet | undefined => {
+            const args = argNodes.map((arg) => this.expression(arg));
+            const shellless = this.ctx.shelllessRepo.get(
+              callback,
+              args,
+            );
+            if (!shellless) {
+              return undefined;
+            }
+
+            const converted = args.map((s, idx) => {
+              const argType = shellless.argTypes[idx] as AnyData;
+              return tryConvertSnippet(s, argType, /* verbose */ false);
+            });
+
+            return this.ctx.withResetIndentLevel(() => {
+              const snippet = this.ctx.resolve(shellless);
+              return snip(
+                stitch`${snippet.value}(${converted})`,
+                snippet.dataType,
+                /* origin */ 'runtime',
+              );
+            });
+          },
         );
-        if (shellless) {
-          const converted = args.map((s, idx) => {
-            const argType = shellless.argTypes[idx] as AnyData;
-            return tryConvertSnippet(s, argType, /* verbose */ false);
-          });
 
-          return this.ctx.withResetIndentLevel(() => {
-            const snippet = this.ctx.resolve(shellless);
-            return snip(
-              stitch`${snippet.value}(${converted})`,
-              snippet.dataType,
-              /* origin */ 'runtime',
-            );
-          });
+        if (shelllessCall) {
+          return shelllessCall;
         }
 
         throw new Error(

packages/typegpu/tests/tgpuGenericFn.test.ts

@@ -0,0 +1,90 @@
+import { describe, expect } from 'vitest';
+import * as d from '../src/data/index.ts';
+import tgpu from '../src/index.ts';
+import { it } from './utils/extendedIt.ts';
+
+describe('TgpuGenericFn - shellless callback wrapper', () => {
+  it('generates only one definition when both original and wrapped function are used', () => {
+    const countAccess = tgpu['~unstable'].accessor(d.f32, 2);
+
+    const getDouble = () => {
+      'use gpu';
+      return countAccess.$ * 2;
+    };
+
+    const getDouble4 = tgpu.fn(getDouble);
+
+    const main = () => {
+      'use gpu';
+      const original = getDouble();
+      const wrapped = getDouble4();
+      return original + wrapped;
+    };
+
+    expect(tgpu.resolve([main])).toMatchInlineSnapshot(`
+      "fn getDouble() -> f32 {
+        return 4f;
+      }
+
+      fn main() -> f32 {
+        let original = getDouble();
+        let wrapped = getDouble();
+        return (original + wrapped);
+      }"
+    `);
+  });
+
+  it('works when only the wrapped function is used', () => {
+    const countAccess = tgpu['~unstable'].accessor(d.f32, 0);
+
+    const getDouble = () => {
+      'use gpu';
+      return countAccess.$ * 2;
+    };
+
+    const getDouble4 = tgpu.fn(getDouble);
+
+    const main = () => {
+      'use gpu';
+      return getDouble4();
+    };
+
+    const wgsl = tgpu.resolve([main]);
+    expect(tgpu.resolve([main])).toMatchInlineSnapshot(`
+      "fn getDouble() -> f32 {
+        return 0f;
+      }
+
+      fn main() -> f32 {
+        return getDouble();
+      }"
+    `);
+  });
+
+  it('does not duplicate the same function', () => {
+    const countAccess = tgpu['~unstable'].accessor(d.f32, 0);
+
+    const getDouble = () => {
+      'use gpu';
+      return countAccess.$ * 2;
+    };
+
+    const getDouble4 = tgpu.fn(getDouble);
+
+    const main = () => {
+      'use gpu';
+      return getDouble4() + getDouble4();
+    };
+
+    const wgsl = tgpu.resolve([main]);
+    expect(tgpu.resolve([main])).toMatchInlineSnapshot(`
+      "fn getDouble() -> f32 {
+        return 0f;
+      }
+
+      fn main() -> f32 {
+        return (getDouble() + getDouble());
+      }"
+    `);
+  });
+});