Overhaul exceptions with tracebacks; 'except Type...'

src/chunk.h

@@ -49,6 +49,7 @@ typedef enum {
 	OP_SUBTRACT,
 	OP_SWAP,
 	OP_TRUE,
+	OP_FILTER_EXCEPT,
 
 	OP_CALL = 64,
 	OP_CLASS,

src/compiler.c

@@ -191,7 +191,7 @@ static void and_(int canAssign);
 static KrkToken classDeclaration();
 static void declareVariable();
 static void namedVariable(KrkToken name, int canAssign);
-static void addLocal(KrkToken name);
+static Local * addLocal(KrkToken name);
 static void string(int canAssign);
 static KrkToken decorator(size_t level, FunctionType type);
 static void call(int canAssign);
@@ -1536,7 +1536,8 @@ static void tryStatement() {
 	/* Make sure we are in a local scope so this ends up on the stack */
 	beginScope();
 	int tryJump = emitJump(OP_PUSH_TRY);
-	addLocal(syntheticToken("exception"));
+	/* We'll rename this later, but it needs to be on the stack now as it represents the exception handler */
+	Local * exceptionObject = addLocal(syntheticToken(""));
 	defineVariable(0);
 
 	beginScope();
@@ -1553,6 +1554,16 @@ static void tryStatement() {
 			advance();
 		}
 		if (match(TOKEN_EXCEPT)) {
+			if (!check(TOKEN_COLON) && !check(TOKEN_AS)) {
+				expression();
+				emitByte(OP_FILTER_EXCEPT);
+			}
+			if (match(TOKEN_AS)) {
+				consume(TOKEN_IDENTIFIER, "Expected identifier after 'as'");
+				exceptionObject->name = parser.previous;
+			} else {
+				exceptionObject->name = syntheticToken("exception");
+			}
 			consume(TOKEN_COLON, "Expect ':' after except.");
 			beginScope();
 			block(blockWidth,"except");
@@ -2428,7 +2439,7 @@ static ssize_t resolveLocal(Compiler * compiler, KrkToken * name) {
 	return -1;
 }
 
-static void addLocal(KrkToken name) {
+static Local * addLocal(KrkToken name) {
 	if (current->localCount + 1 > current->localsSpace) {
 		size_t old = current->localsSpace;
 		current->localsSpace = GROW_CAPACITY(old);
@@ -2449,6 +2460,7 @@ static void addLocal(KrkToken name) {
 	current->function->localNames[current->function->localNameCount].deathday = 0;
 	current->function->localNames[current->function->localNameCount].name = krk_copyString(name.start, name.length);
 	current->function->localNameCount++;
+	return local;
 }
 
 static void declareVariable() {

src/obj_function.c

@@ -3,6 +3,7 @@
 #include "value.h"
 #include "memory.h"
 #include "util.h"
+#include "debug.h"
 
 /* function.__doc__ */
 static KrkValue _closure_get_doc(int argc, KrkValue argv[], int hasKw) {
@@ -24,13 +25,15 @@ static KrkValue _bound_get_doc(int argc, KrkValue argv[], int hasKw) {
 /* Check for and return the name of a native function as a string object */
 static KrkValue nativeFunctionName(KrkValue func) {
 	const char * string = ((KrkNative*)AS_OBJECT(func))->name;
+	if (!string) return OBJECT_VAL(S("<unnamed>"));
 	size_t len = strlen(string);
 	return OBJECT_VAL(krk_copyString(string,len));
 }
 
 /* function.__name__ */
 static KrkValue _closure_get_name(int argc, KrkValue argv[], int hasKw) {
-	if (!IS_CLOSURE(argv[0])) return nativeFunctionName(argv[0]);
+	if (IS_NATIVE(argv[0])) return nativeFunctionName(argv[0]);
+	else if (!IS_CLOSURE(argv[0])) return krk_runtimeError(vm.exceptions->typeError, "'%s' is neither a closure nor a native", krk_typeName(argv[0]));
 	return AS_CLOSURE(argv[0])->function->name ? OBJECT_VAL(AS_CLOSURE(argv[0])->function->name) : OBJECT_VAL(S(""));
 }
 
@@ -40,9 +43,22 @@ static KrkValue _bound_get_name(int argc, KrkValue argv[], int hasKw) {
 	return _closure_get_name(1, (KrkValue[]){OBJECT_VAL(boundMethod->method)}, hasKw);
 }
 
+static KrkValue _closure_ip_to_line(int argc, KrkValue argv[], int hasKw) {
+	if (argc < 2) return krk_runtimeError(vm.exceptions->argumentError, "%s() expects exactly 2 arguments", "ip_to_line");
+	if (!IS_CLOSURE(argv[0])) return NONE_VAL();
+	if (!IS_INTEGER(argv[1])) return TYPE_ERROR(int,argv[1]);
+	return INTEGER_VAL(krk_lineNumber(&AS_CLOSURE(argv[0])->function->chunk, AS_INTEGER(argv[1])));
+}
+
+static KrkValue _bound_ip_to_line(int argc, KrkValue argv[], int hasKw) {
+	KrkBoundMethod * boundMethod = AS_BOUND_METHOD(argv[0]);
+	return _closure_ip_to_line(1, (KrkValue[]){OBJECT_VAL(boundMethod->method)}, hasKw);
+}
+
 /* function.__str__ / function.__repr__ */
 static KrkValue _closure_str(int argc, KrkValue argv[], int hasKw) {
 	KrkValue s = _closure_get_name(argc, argv, hasKw);
+	if (!IS_STRING(s)) return NONE_VAL();
 	krk_push(s);
 
 	size_t len = AS_STRING(s)->length + sizeof("<function >");
@@ -114,6 +130,7 @@ void _createAndBind_functionClass(void) {
 	krk_defineNative(&vm.baseClasses->functionClass->methods, ":__name__", _closure_get_name);
 	krk_defineNative(&vm.baseClasses->functionClass->methods, ":__file__", _closure_get_file);
 	krk_defineNative(&vm.baseClasses->functionClass->methods, ":__args__", _closure_get_argnames);
+	krk_defineNative(&vm.baseClasses->functionClass->methods, "_ip_to_line", _closure_ip_to_line);
 	krk_finalizeClass(vm.baseClasses->functionClass);
 
 	ADD_BASE_CLASS(vm.baseClasses->methodClass, "method", vm.baseClasses->objectClass);
@@ -123,5 +140,6 @@ void _createAndBind_functionClass(void) {
 	krk_defineNative(&vm.baseClasses->methodClass->methods, ":__name__", _bound_get_name);
 	krk_defineNative(&vm.baseClasses->methodClass->methods, ":__file__", _bound_get_file);
 	krk_defineNative(&vm.baseClasses->methodClass->methods, ":__args__", _bound_get_argnames);
+	krk_defineNative(&vm.baseClasses->methodClass->methods, "_ip_to_line", _bound_ip_to_line);
 	krk_finalizeClass(vm.baseClasses->methodClass);
 }

src/opcodes.h

@@ -36,6 +36,7 @@ SIMPLE(OP_IS)
 SIMPLE(OP_POW)
 SIMPLE(OP_CREATE_PROPERTY)
 SIMPLE(OP_CLEANUP_WITH)
+SIMPLE(OP_FILTER_EXCEPT)
 CONSTANT(OP_DEFINE_GLOBAL,(void)0)
 CONSTANT(OP_CONSTANT,(void)0)
 CONSTANT(OP_GET_GLOBAL,(void)0)

src/vm.c

@@ -167,47 +167,66 @@ static void dumpStack(CallFrame * frame) {
  * the source file and print the corresponding line.
  */
 void krk_dumpTraceback() {
-	if (krk_currentThread.frameCount) {
-		fprintf(stderr, "Traceback (most recent call last):\n");
-		for (size_t i = 0; i <= krk_currentThread.frameCount - 1; i++) {
-			CallFrame * frame = &krk_currentThread.frames[i];
-			KrkFunction * function = frame->closure->function;
-			size_t instruction = frame->ip - function->chunk.code - 1;
-			int lineNo = (int)krk_lineNumber(&function->chunk, instruction);
-			fprintf(stderr, "  File \"%s\", line %d, in %s\n",
-				(function->chunk.filename ? function->chunk.filename->chars : "?"),
-				lineNo,
-				(function->name ? function->name->chars : "(unnamed)"));
-			if (function->chunk.filename) {
-				FILE * f = fopen(function->chunk.filename->chars, "r");
-				if (f) {
-					int line = 1;
-					do {
-						char c = fgetc(f);
-						if (c < -1) break;
-						if (c == '\n') {
-							line++;
-							continue;
-						}
-						if (line == lineNo) {
-							fprintf(stderr,"    ");
-							while (c == ' ') c = fgetc(f);
-							do {
-								fputc(c, stderr);
-								c = fgetc(f);
-							} while (!feof(f) && c > 0 && c != '\n');
-							fprintf(stderr, "\n");
-							break;
-						}
-					} while (!feof(f));
-					fclose(f);
+	if (!krk_valuesEqual(krk_currentThread.currentException,NONE_VAL())) {
+		krk_push(krk_currentThread.currentException);
+		KrkValue tracebackEntries;
+		if (IS_INSTANCE(krk_currentThread.currentException)
+			&& krk_tableGet(&AS_INSTANCE(krk_currentThread.currentException)->fields, OBJECT_VAL(S("traceback")), &tracebackEntries)
+			&& IS_list(tracebackEntries) && AS_LIST(tracebackEntries)->count > 0) {
+			/* This exception has a traceback we can print. */
+			fprintf(stderr, "Traceback (most recent call last):\n");
+			for (size_t i = 0; i < AS_LIST(tracebackEntries)->count; ++i) {
+
+				/* Quietly skip invalid entries as we don't want to bother printing explanatory text for them */
+				if (!IS_TUPLE(AS_LIST(tracebackEntries)->values[i])) continue;
+				KrkTuple * entry = AS_TUPLE(AS_LIST(tracebackEntries)->values[i]);
+				if (entry->values.count != 2) continue;
+				if (!IS_CLOSURE(entry->values.values[0])) continue;
+				if (!IS_INTEGER(entry->values.values[1])) continue;
+
+				/* Get the function and instruction index from this traceback entry */
+				KrkClosure * closure = AS_CLOSURE(entry->values.values[0]);
+				KrkFunction * function = closure->function;
+				size_t instruction = AS_INTEGER(entry->values.values[1]);
+
+				/* Calculate the line number */
+				int lineNo = (int)krk_lineNumber(&function->chunk, instruction);
+
+				/* Print the simple stuff that we already know */
+				fprintf(stderr, "  File \"%s\", line %d, in %s\n",
+					(function->chunk.filename ? function->chunk.filename->chars : "?"),
+					lineNo,
+					(function->name ? function->name->chars : "(unnamed)"));
+
+				/* Try to open the file */
+				if (function->chunk.filename) {
+					FILE * f = fopen(function->chunk.filename->chars, "r");
+					if (f) {
+						int line = 1;
+						do {
+							char c = fgetc(f);
+							if (c < -1) break;
+							if (c == '\n') {
+								line++;
+								continue;
+							}
+							if (line == lineNo) {
+								fprintf(stderr,"    ");
+								while (c == ' ') c = fgetc(f);
+								do {
+									fputc(c, stderr);
+									c = fgetc(f);
+								} while (!feof(f) && c > 0 && c != '\n');
+								fprintf(stderr, "\n");
+								break;
+							}
+						} while (!feof(f));
+						fclose(f);
+					}
 				}
 			}
 		}
-	}
 
-	if (!krk_valuesEqual(krk_currentThread.currentException,NONE_VAL())) {
-		krk_push(krk_currentThread.currentException);
 		/* Is this a SyntaxError? Handle those specially. */
 		if (krk_isInstanceOf(krk_currentThread.currentException, vm.exceptions->syntaxError)) {
 			KrkValue result = krk_callSimple(OBJECT_VAL(krk_getType(krk_currentThread.currentException)->_tostr), 1, 0);
@@ -228,6 +247,37 @@ void krk_dumpTraceback() {
 	}
 }
 
+/**
+ * Attach a traceback to the current exception object, if it doesn't already have one.
+ */
+static void attachTraceback(void) {
+	if (IS_INSTANCE(krk_currentThread.currentException)) {
+		KrkInstance * theException = AS_INSTANCE(krk_currentThread.currentException);
+
+		/* If there already is a traceback, don't add a new one; this exception was re-raised. */
+		KrkValue existing;
+		if (krk_tableGet(&theException->fields, OBJECT_VAL(S("traceback")), &existing)) return;
+
+		KrkValue tracebackList = krk_list_of(0,NULL,0);
+		krk_push(tracebackList);
+		/* Build the traceback object */
+		if (krk_currentThread.frameCount) {
+			for (size_t i = 0; i < krk_currentThread.frameCount; i++) {
+				CallFrame * frame = &krk_currentThread.frames[i];
+				KrkTuple * tbEntry = krk_newTuple(2);
+				krk_push(OBJECT_VAL(tbEntry));
+				tbEntry->values.values[tbEntry->values.count++] = OBJECT_VAL(frame->closure);
+				tbEntry->values.values[tbEntry->values.count++] = INTEGER_VAL(frame->ip - frame->closure->function->chunk.code - 1);
+				krk_tupleUpdateHash(tbEntry);
+				krk_writeValueArray(AS_LIST(tracebackList), OBJECT_VAL(tbEntry));
+				krk_pop();
+			}
+		}
+		krk_attachNamedValue(&theException->fields, "traceback", tracebackList);
+		krk_pop();
+	} /* else: probably a legacy 'raise str', just don't bother. */
+}
+
 /**
  * Raise an exception. Creates an exception object of the requested type
  * and formats a message string to attach to it. Exception classes are
@@ -254,6 +304,7 @@ KrkValue krk_runtimeError(KrkClass * type, const char * fmt, ...) {
 
 	/* Set the current exception to be picked up by handleException */
 	krk_currentThread.currentException = OBJECT_VAL(exceptionObject);
+	attachTraceback();
 	return NONE_VAL();
 }
 
@@ -1831,6 +1882,7 @@ static KrkValue run() {
 			case OP_POP:   krk_pop(); break;
 			case OP_RAISE: {
 				krk_currentThread.currentException = krk_pop();
+				attachTraceback();
 				krk_currentThread.flags |= KRK_HAS_EXCEPTION;
 				goto _finishException;
 			}
@@ -1945,6 +1997,28 @@ static KrkValue run() {
 				krk_push(OBJECT_VAL(newProperty));
 				break;
 			}
+			case OP_FILTER_EXCEPT: {
+				int isMatch = 0;
+				if (IS_CLASS(krk_peek(0)) && krk_isInstanceOf(krk_peek(1), AS_CLASS(krk_peek(0)))) {
+					isMatch = 1;
+				} if (IS_TUPLE(krk_peek(0))) {
+					for (size_t i = 0; i < AS_TUPLE(krk_peek(0))->values.count; ++i) {
+						if (IS_CLASS(AS_TUPLE(krk_peek(0))->values.values[i]) && krk_isInstanceOf(krk_peek(1), AS_CLASS(AS_TUPLE(krk_peek(0))->values.values[i]))) {
+							isMatch = 1;
+							break;
+						}
+					}
+				}
+				if (!isMatch) {
+					/* Restore and re-raise the exception if it didn't match. */
+					krk_currentThread.currentException = krk_peek(1);
+					krk_currentThread.flags |= KRK_HAS_EXCEPTION;
+					goto _finishException;
+				}
+				/* Else pop the filter value */
+				krk_pop();
+				break;
+			}
 
 			/*
 			 * Two-byte operands

test/testExceptionTracebacks.krk

@@ -0,0 +1,17 @@
+def doTheThing(excp):
+    try:
+        try:
+            raise excp
+        except (TypeError, ValueError):
+            print("Caught a", repr(exception))
+            for i in exception.traceback:
+                let func, instr = i
+                print(f"  File '{func.__file__}', line {func._ip_to_line(instr)}, in {func.__name__}")
+    except NameError:
+        print("That's a name error!")
+
+
+doTheThing(TypeError("A type error"))
+doTheThing(ValueError("A value error"))
+doTheThing(NameError("A name error"))
+

test/testExceptionTracebacks.krk.expect

@@ -0,0 +1,7 @@
+Caught a TypeError('A type error')
+  File 'test/testExceptionTracebacks.krk', line 14, in __main__
+  File 'test/testExceptionTracebacks.krk', line 4, in doTheThing
+Caught a ValueError('A value error')
+  File 'test/testExceptionTracebacks.krk', line 15, in __main__
+  File 'test/testExceptionTracebacks.krk', line 4, in doTheThing
+That's a name error!

test/testFilteredExceptions.krk

@@ -0,0 +1,14 @@
+def doTheThing(excp):
+    try:
+        try:
+            raise excp
+        except (TypeError, ValueError) as e:
+            print("Caught a", repr(e))
+    except NameError:
+        print("That's a name error!")
+
+
+doTheThing(TypeError("A type error"))
+doTheThing(ValueError("A value error"))
+doTheThing(NameError("A name error"))
+

test/testFilteredExceptions.krk.expect

@@ -0,0 +1,3 @@
+Caught a TypeError('A type error')
+Caught a ValueError('A value error')
+That's a name error!