fix: forward compilation errors, fix HMR

Author: CodyJasonBennett

src/index.js

@@ -15,11 +15,6 @@ let slangPromise = null
  * @returns {import('vite').PluginOption}
  */
 function viteSlang(options = { target: 'WGSL' }) {
-  /**
-   * @type {import('./slang-2025.15-wasm/slang-wasm.js').Session | null}
-   */
-  let session = null
-
   return {
     name: 'vite-slang',
     async transform(code, id) {
@@ -28,11 +23,14 @@ function viteSlang(options = { target: 'WGSL' }) {
       // For now, we only handle files with a .slang file extension. These are transformed as source code.
       if (!id.endsWith('.slang')) return
 
-      // Lazy load Slang WASM so this module can be used in ESM/CJS/UMD contexts (no top-level-await)
-      if (!slangPromise) slangPromise = slangModule()
-      const slang = await slangPromise
+      /** @type {import('./slang-2025.15-wasm/slang-wasm.js').Session | null} */
+      let session = null
+
+      try {
+        // Lazy load Slang WASM so this module can be used in ESM/CJS/UMD contexts (no top-level-await)
+        if (!slangPromise) slangPromise = slangModule()
+        const slang = await slangPromise
 
-      if (!session) {
         let wasmCompileTarget = -1
         for (const target of slang.getCompileTargets()) {
           if (target.name == options.target) {
@@ -43,44 +41,54 @@ function viteSlang(options = { target: 'WGSL' }) {
         // TODO: under which scenarios is a session null? Examples expect GlobalSession but not a Session?
         const globalSession = slang.createGlobalSession()
         session = globalSession.createSession(wasmCompileTarget)
-      }
 
-      // TODO: module stitching and/or non-standard preprocessor unfolding?
-      /** @type {import('./slang-2025.15-wasm/slang-wasm.js').Module} */
-      const module = session.loadModuleFromSource(code, 'shader', id)
-      /** @type {import('./slang-2025.15-wasm/slang-wasm.js').Module[]} */
-      const components = [module]
+        // TODO: module stitching and/or non-standard preprocessor unfolding?
+        /** @type {import('./slang-2025.15-wasm/slang-wasm.js').Module} */
+        const module = session.loadModuleFromSource(code, 'shader', id)
+        /** @type {import('./slang-2025.15-wasm/slang-wasm.js').Module[]} */
 
-      // TODO: surely, there's a better way to reflect the program and get a top-level layout?
-      const count = module.getDefinedEntryPointCount()
-      for (let i = 0; i < count; i++) {
-        /** @type {import('./slang-2025.15-wasm/slang-wasm.js').EntryPoint} */
-        const entryPoint = module.getDefinedEntryPoint(i)
-        const program = session.createCompositeComponentType([entryPoint, 1])
-        const layout = program.getLayout(0).toJsonObject()
-        const { name, stage } = layout.entryPoints[0]
-        components.push(module.findAndCheckEntryPoint(name, SLANG_STAGES[stage]))
-      }
+        // Surface compilation errors
+        if (!module) {
+          const error = slang.getLastError()
+          throw new Error(`${error.type} error: ${error.message}`)
+        }
+
+        // TODO: is there a way to instead infer based on SV_VertexID or SV_Target?
+        const count = module.getDefinedEntryPointCount()
+        if (count === 0) {
+          throw new Error(
+            'An entrypoint must be defined with a shader stage attribute! Try adding [shader("fragment")] before your entrypoint method.',
+          )
+        }
 
-      /** @type {import('./slang-2025.15-wasm/slang-wasm.js').ComponentType} */
-      const linkedProgram = session.createCompositeComponentType(components).link()
+        // TODO: surely, there's a better way to reflect the program and get a top-level layout?
+        const components = [module]
+        for (let i = 0; i < count; i++) {
+          /** @type {import('./slang-2025.15-wasm/slang-wasm.js').EntryPoint} */
+          const entryPoint = module.getDefinedEntryPoint(i)
+          const program = session.createCompositeComponentType([entryPoint, 1])
+          const layout = program.getLayout(0).toJsonObject()
+          const { name, stage } = layout.entryPoints[0]
+          components.push(module.findAndCheckEntryPoint(name, SLANG_STAGES[stage]))
+        }
 
-      code = ''
-      for (let i = 0; i < count; i++) {
-        code += linkedProgram.getEntryPointCode(i /* entryPointIndex */, 0 /* targetIndex */) + '\n'
-      }
-      code.trim()
+        /** @type {import('./slang-2025.15-wasm/slang-wasm.js').ComponentType} */
+        const linkedProgram = session.createCompositeComponentType(components).link()
 
-      if (code == '') {
-        const error = slang.getLastError()
-        throw new Error(`${error.type} error: ${error.message}`)
-      }
+        code = ''
+        for (let i = 0; i < count; i++) {
+          code += linkedProgram.getEntryPointCode(i /* entryPointIndex */, 0 /* targetIndex */) + '\n'
+        }
+        code.trim()
 
-      return transformWithEsbuild(code, id, {
-        format: 'esm',
-        loader: 'text',
-        sourcemap: 'external', // TODO: pass to WebGPU API?
-      })
+        return transformWithEsbuild(code, id, {
+          format: 'esm',
+          loader: 'text',
+          sourcemap: 'external', // TODO: pass to WebGPU API?
+        })
+      } finally {
+        if (session) session.delete()
+      }
     },
   }
 }