Wasm: Implement checked nullPointers.

scala-js · sjrd · Aug 30, 2024 · Jun 24, 2024 · Jun 24, 2024 · Jun 24, 2024
commit 58af468534ea2373d1b85fb9f6e803c40d1e18ad
diff --git a/linker/shared/src/main/scala/org/scalajs/linker/backend/WebAssemblyLinkerBackend.scala b/linker/shared/src/main/scala/org/scalajs/linker/backend/WebAssemblyLinkerBackend.scala
@@ -36,11 +36,6 @@ final class WebAssemblyLinkerBackend(config: LinkerBackendImpl.Config)
     coreSpec.moduleKind == ModuleKind.ESModule,
     s"The WebAssembly backend only supports ES modules; was ${coreSpec.moduleKind}."
   )
-  require(
-    coreSpec.semantics.nullPointers == CheckedBehavior.Unchecked,
-    "The WebAssembly backend currently only supports CheckedBehavior.Unchecked semantics; " +
-    s"was ${coreSpec.semantics}."
-  )
   require(
     coreSpec.semantics.strictFloats,
     "The WebAssembly backend only supports strict float semantics."

diff --git a/linker/shared/src/main/scala/org/scalajs/linker/backend/wasmemitter/CoreWasmLib.scala b/linker/shared/src/main/scala/org/scalajs/linker/backend/wasmemitter/CoreWasmLib.scala
@@ -627,6 +627,10 @@ final class CoreWasmLib(coreSpec: CoreSpec) {
       genCheckedStringCharAt()
     }
 
+    if (semantics.nullPointers != CheckedBehavior.Unchecked) {
+      genThrowNullPointerException()
+    }
+
     if (semantics.moduleInit == CheckedBehavior.Fatal) {
       genThrowModuleInitError()
     }
@@ -1361,6 +1365,26 @@ final class CoreWasmLib(coreSpec: CoreSpec) {
     fb.buildAndAddToModule()
   }
 
+  /** `throwNullPointerException: void -> void`.
+   *
+   *  This function always throws. It should be followed by an `unreachable`
+   *  statement.
+   */
+  private def genThrowNullPointerException()(implicit ctx: WasmContext): Unit = {
+    val typeDataType = RefType(genTypeID.typeData)
+
+    val fb = newFunctionBuilder(genFunctionID.throwNullPointerException)
+
+    maybeWrapInUBE(fb, semantics.nullPointers) {
+      genNewScalaClass(fb, NullPointerExceptionClass, NoArgConstructorName) {
+      }
+    }
+    fb += ExternConvertAny
+    fb += Throw(genTagID.exception)
+
+    fb.buildAndAddToModule()
+  }
+
   /** Generates the `arrayGet.x` functions. */
   private def genArrayGets()(implicit ctx: WasmContext): Unit = {
     for (baseRef <- arrayBaseRefs)
@@ -2248,10 +2272,21 @@ final class CoreWasmLib(coreSpec: CoreSpec) {
     val valueParam = fb.addParam("value", RefType.any)
     fb.setResultType(RefType.any)
 
-    fb += LocalGet(valueParam)
-    fb += Call(genFunctionID.anyGetTypeData)
-    fb += RefAsNonNull // NPE for null.getName()
-    fb += ReturnCall(genFunctionID.typeDataName)
+    if (semantics.nullPointers == CheckedBehavior.Unchecked) {
+      fb += LocalGet(valueParam)
+      fb += Call(genFunctionID.anyGetTypeData)
+      fb += RefAsNonNull // NPE for null.getName()
+      fb += ReturnCall(genFunctionID.typeDataName)
+    } else {
+      fb.block() { npeLabel =>
+        fb += LocalGet(valueParam)
+        fb += Call(genFunctionID.anyGetTypeData)
+        fb += BrOnNull(npeLabel) // NPE for null.getName()
+        fb += ReturnCall(genFunctionID.typeDataName)
+      }
+      fb += Call(genFunctionID.throwNullPointerException)
+      fb += Unreachable
+    }
 
     fb.buildAndAddToModule()
   }

diff --git a/linker/shared/src/main/scala/org/scalajs/linker/backend/wasmemitter/Emitter.scala b/linker/shared/src/main/scala/org/scalajs/linker/backend/wasmemitter/Emitter.scala
@@ -419,6 +419,10 @@ object Emitter {
             StringArgConstructorName)
       },
 
+      cond(nullPointers != Unchecked) {
+        instantiateClass(NullPointerExceptionClass, NoArgConstructorName)
+      },
+
       cond(stringIndexOutOfBounds != Unchecked) {
         instantiateClass(StringIndexOutOfBoundsExceptionClass,
             IntArgConstructorName)