Enforce Error type in throw statements

Throw statements now require the thrown value to be of type Error or a subclass. Added a diagnostic message for invalid throw types, updated the abort implementation to throw Error when exception handling is enabled, and added tests for invalid throw types.

Author: BlobMaster41

src/compiler.ts

@@ -3024,6 +3024,19 @@ export class Compiler extends DiagnosticEmitter {
     if (this.options.hasFeature(Feature.ExceptionHandling)) {
       // Compile the thrown value - should be Error or subclass
       let valueExpr = this.compileExpression(statement.value, Type.auto);
+      let valueType = this.currentType;
+
+      // Verify that the thrown type is Error or a subclass
+      let errorInstance = this.program.errorInstance;
+      let classReference = valueType.getClass();
+      if (!classReference || !classReference.isAssignableTo(errorInstance)) {
+        this.error(
+          DiagnosticCode.Only_Error_or_its_subclasses_can_be_thrown_but_found_type_0,
+          statement.value.range,
+          valueType.toString()
+        );
+        return module.unreachable();
+      }
 
       // Ensure exception tag exists
       let tagName = this.ensureExceptionTag();

src/diagnosticMessages.json

@@ -52,6 +52,7 @@
   "Initializer, definitive assignment or nullable type expected.": 238,
   "Definitive assignment has no effect on local variables.": 239,
   "Ambiguous operator overload '{0}' (conflicting overloads '{1}' and '{2}').": 240,
+  "Only Error or its subclasses can be thrown, but found type '{0}'.": 241,
 
   "Importing the table disables some indirect call optimizations.": 901,
   "Exporting the table disables some indirect call optimizations.": 902,

src/program.ts

@@ -636,6 +636,14 @@ export class Program extends DiagnosticEmitter {
   }
   private _stringInstance: Class | null = null;
 
+  /** Gets the standard `Error` instance. */
+  get errorInstance(): Class {
+    let cached = this._errorInstance;
+    if (!cached) this._errorInstance = cached = this.requireClass(CommonNames.Error);
+    return cached;
+  }
+  private _errorInstance: Class | null = null;
+
   /** Gets the standard `RegExp` instance. */
   get regexpInstance(): Class {
     let cached = this._regexpInstance;

std/assembly/builtins.ts

@@ -2603,13 +2603,32 @@ export abstract class i31 { // FIXME: usage of 'new' requires a class :(
 // @ts-ignore: decorator
 @external("env", "abort")
 @external.js("throw Error(`${message} in ${fileName}:${lineNumber}:${columnNumber}`);")
-declare function abort(
+declare function __abort_impl(
   message?: string | null,
   fileName?: string | null,
   lineNumber?: u32,
   columnNumber?: u32
 ): void;
 
+// When exception-handling is enabled, abort throws an Error that can be caught.
+// When disabled, it calls the external abort function (host implementation).
+function abort(
+  message: string | null = null,
+  fileName: string | null = null,
+  lineNumber: u32 = 0,
+  columnNumber: u32 = 0
+): void {
+  if (isDefined(ASC_FEATURE_EXCEPTION_HANDLING)) {
+    let fullMessage = message ? message : "abort";
+    if (fileName) {
+      fullMessage += " in " + fileName + ":" + lineNumber.toString() + ":" + columnNumber.toString();
+    }
+    throw new Error(fullMessage);
+  } else {
+    __abort_impl(message, fileName, lineNumber, columnNumber);
+  }
+}
+
 // @ts-ignore: decorator
 @external("env", "trace")
 @external.js("console.log(message, ...[a0, a1, a2, a3, a4].slice(0, n));")

tests/compiler/exceptions.debug.wat

@@ -499,3 +499,80 @@ function testReturnInFinallySuppressesException(): i32 {
 }
 assert(testReturnInFinallySuppressesException() == 42);
 assert(finallyReturnSuppressedExceptionRan);
+
+// ============================================================
+// Tests for catching abort() and runtime errors
+// ============================================================
+
+// Test catching abort()
+function testCatchAbort(): bool {
+  let caught = false;
+  try {
+    abort("this should be catchable");
+  } catch (e) {
+    caught = true;
+    // Verify we got an Error with the abort message
+    assert(e.message.includes("this should be catchable"));
+  }
+  return caught;
+}
+assert(testCatchAbort());
+
+// Test catching runtime errors from __new (allocation too large)
+function testCatchRuntimeError(): bool {
+  let caught = false;
+  try {
+    // Try to allocate an impossibly large object
+    // This should trigger an allocation error in the runtime
+    __new(usize.MAX_VALUE, idof<ArrayBuffer>());
+  } catch (e) {
+    caught = true;
+    // Should have caught an allocation error
+    assert(e.message.length > 0);
+  }
+  return caught;
+}
+assert(testCatchRuntimeError());
+
+// Test that abort in a function can be caught by the caller
+function functionThatAborts(): void {
+  abort("abort from function");
+}
+
+function testCatchAbortFromFunction(): bool {
+  let caught = false;
+  try {
+    functionThatAborts();
+  } catch (e) {
+    caught = true;
+    assert(e.message.includes("abort from function"));
+  }
+  return caught;
+}
+assert(testCatchAbortFromFunction());
+
+// Test catch variable is properly typed as Error
+function testCatchVariableType(): bool {
+  try {
+    throw new Error("type test");
+  } catch (e) {
+    // e should be typed as Error, so we can access message directly
+    let msg: string = e.message;
+    return msg == "type test";
+  }
+  return false;
+}
+assert(testCatchVariableType());
+
+// Test catching custom Error subclass (use existing CustomError class)
+function testCatchCustomError2(): bool {
+  try {
+    throw new CustomError("custom error 2", 99);
+  } catch (e) {
+    // e is typed as Error, need to cast to access code
+    let custom = e as CustomError;
+    return custom.message == "custom error 2" && custom.code == 99;
+  }
+  return false;
+}
+assert(testCatchCustomError2());

tests/compiler/exceptions.release.wat

@@ -0,0 +1,9 @@
+{
+  "asc_flags": [
+    "--enable", "exception-handling"
+  ],
+  "stderr": [
+    "AS241: Only Error or its subclasses can be thrown, but found type '~lib/string/String'.",
+    "EOF"
+  ]
+}

tests/compiler/exceptions.ts

@@ -0,0 +1,6 @@
+// Test that throwing non-Error types results in a compile error
+
+// This should fail - throwing a string is not allowed
+throw "string error";
+
+ERROR("EOF");