Print the offending line of code in the traceback for SyntaxErrors

raised by the compiler.

XXX For now, text entered into the interactive intepreter is not
printed in the traceback.

Inspired by a patch from Roman Sulzhyk

compile.c:

Add helper fetch_program_text() that opens a file and reads until it
finds the specified line number.  The code is a near duplicate of
similar code in traceback.c.

Modify com_error() to pass two arguments to SyntaxError constructor,
where the second argument contains the offending text when possible.

Modify set_error_location(), now used only by the symtable pass, to
set the text attribute on existing exceptions.

pythonrun.c:

Change parse_syntax_error() to continue of the offset attribute of a
SyntaxError is None.  In this case, it sets offset to -1.

Move code from PyErr_PrintEx() into helper function
print_error_text().  In the helper, only print the caret for a
SyntaxError if offset > 0.

Python/compile.c

@@ -381,60 +381,88 @@ int is_free(int v)
 	return 0;
 }
 
-/* Error message including line number */
+/* com_fetch_program_text will attempt to load the line of text that
+   the exception refers to.  If it fails, it will return NULL but will
+   not set an exception. 
 
-static void
-set_error_location(char *filename, int lineno)
+   XXX The functionality of this function is quite similar to the
+   functionality in tb_displayline() in traceback.c.
+*/
+
+static PyObject *
+fetch_program_text(char *filename, int lineno)
 {
-	PyObject *exc, *v, *tb, *tmp;
+	FILE *fp;
+	int i;
+	char linebuf[1000];
 
-	/* add attributes for the line number and filename for the error */
-	PyErr_Fetch(&exc, &v, &tb);
-	PyErr_NormalizeException(&exc, &v, &tb);
-	tmp = PyInt_FromLong(lineno);
-	if (tmp == NULL)
-		PyErr_Clear();
-	else {
-		if (PyObject_SetAttrString(v, "lineno", tmp))
-			PyErr_Clear();
-		Py_DECREF(tmp);
-	}
-	if (filename != NULL) {
-		tmp = PyString_FromString(filename);
-		if (tmp == NULL)
-			PyErr_Clear();
-		else {
-			if (PyObject_SetAttrString(v, "filename", tmp))
-				PyErr_Clear();
-			Py_DECREF(tmp);
-		}
+	if (filename == NULL || lineno <= 0)
+		return NULL;
+	fp = fopen(filename, "r");
+	if (fp == NULL)
+		return NULL;
+	for (i = 0; i < lineno; i++) {
+		char *pLastChar = &linebuf[sizeof(linebuf) - 2];
+		do {
+			*pLastChar = '\0';
+			if (fgets(linebuf, sizeof linebuf, fp) == NULL)
+				break;
+			/* fgets read *something*; if it didn't get as
+			   far as pLastChar, it must have found a newline
+			   or hit the end of the file;	if pLastChar is \n,
+			   it obviously found a newline; else we haven't
+			   yet seen a newline, so must continue */
+		} while (*pLastChar != '\0' && *pLastChar != '\n');
+	}
+	fclose(fp);
+	if (i == lineno) {
+		char *p = linebuf;
+		while (*p == ' ' || *p == '\t' || *p == '\014')
+			p++;
+		return PyString_FromString(p);
 	}
-	PyErr_Restore(exc, v, tb);
+	return NULL;
 }
 
 static void
 com_error(struct compiling *c, PyObject *exc, char *msg)
 {
-	PyObject *v;
+	PyObject *t = NULL, *v = NULL, *w = NULL, *line = NULL;
+
 	if (c == NULL) {
 		/* Error occurred via symtable call to
 		   is_constant_false */
 		PyErr_SetString(exc, msg);
 		return;
 	}
 	c->c_errors++;
-	if (c->c_lineno <= 1) {
-		/* Unknown line number or single interactive command */
+	if (c->c_lineno < 1 || c->c_interactive) { 
+		/* Unknown line number or interactive input */
 		PyErr_SetString(exc, msg);
 		return;
 	}
 	v = PyString_FromString(msg);
 	if (v == NULL)
 		return; /* MemoryError, too bad */
-	PyErr_SetObject(exc, v);
-	Py_DECREF(v);
 
-	set_error_location(c->c_filename, c->c_lineno);
+	line = fetch_program_text(c->c_filename, c->c_lineno);
+	if (line == NULL) {
+		Py_INCREF(Py_None);
+		line = Py_None;
+	}
+	t = Py_BuildValue("(ziOO)", c->c_filename, c->c_lineno,
+			  Py_None, line);
+	if (t == NULL)
+		goto exit;
+	w = Py_BuildValue("(OO)", v, t);
+	if (w == NULL)
+		goto exit;
+	PyErr_SetObject(exc, w);
+ exit:
+	Py_XDECREF(t);
+	Py_XDECREF(v);
+	Py_XDECREF(w);
+	Py_XDECREF(line);
 }
 
 /* Interface to the block stack */
@@ -3998,6 +4026,43 @@ get_ref_type(struct compiling *c, char *name)
 	return -1; /* can't get here */
 }
 
+/* Helper function for setting lineno and filename */
+
+static void
+set_error_location(char *filename, int lineno)
+{
+	PyObject *exc, *v, *tb, *tmp;
+
+	/* add attributes for the line number and filename for the error */
+	PyErr_Fetch(&exc, &v, &tb);
+	PyErr_NormalizeException(&exc, &v, &tb);
+	tmp = PyInt_FromLong(lineno);
+	if (tmp == NULL)
+		PyErr_Clear();
+	else {
+		if (PyObject_SetAttrString(v, "lineno", tmp))
+			PyErr_Clear();
+		Py_DECREF(tmp);
+	}
+	if (filename != NULL) {
+		tmp = PyString_FromString(filename);
+		if (tmp == NULL)
+			PyErr_Clear();
+		else {
+			if (PyObject_SetAttrString(v, "filename", tmp))
+				PyErr_Clear();
+			Py_DECREF(tmp);
+		}
+
+		tmp = fetch_program_text(filename, lineno);
+		if (tmp) {
+			PyObject_SetAttrString(v, "text", tmp);
+			Py_DECREF(tmp);
+		}
+	}
+	PyErr_Restore(exc, v, tb);
+}
+
 static int
 symtable_build(struct compiling *c, node *n)
 {

Python/pythonrun.c

@@ -693,12 +693,18 @@ parse_syntax_error(PyObject *err, PyObject **message, char **filename,
 
 	if (!(v = PyObject_GetAttrString(err, "offset")))
 		goto finally;
-	hold = PyInt_AsLong(v);
-	Py_DECREF(v);
-	v = NULL;
-	if (hold < 0 && PyErr_Occurred())
-		goto finally;
-	*offset = (int)hold;
+	if (v == Py_None) {
+		*offset = -1;
+		Py_DECREF(v);
+		v = NULL;
+	} else {
+		hold = PyInt_AsLong(v);
+		Py_DECREF(v);
+		v = NULL;
+		if (hold < 0 && PyErr_Occurred())
+			goto finally;
+		*offset = (int)hold;
+	}
 
 	if (!(v = PyObject_GetAttrString(err, "text")))
 		goto finally;
@@ -720,6 +726,40 @@ PyErr_Print(void)
 	PyErr_PrintEx(1);
 }
 
+static void
+print_error_text(PyObject *f, int offset, char *text)
+{
+	char *nl;
+	if (offset >= 0) {
+		if (offset > 0 && offset == (int)strlen(text))
+			offset--;
+		for (;;) {
+			nl = strchr(text, '\n');
+			if (nl == NULL || nl-text >= offset)
+				break;
+			offset -= (nl+1-text);
+			text = nl+1;
+		}
+		while (*text == ' ' || *text == '\t') {
+			text++;
+			offset--;
+		}
+	}
+	PyFile_WriteString("    ", f);
+	PyFile_WriteString(text, f);
+	if (*text == '\0' || text[strlen(text)-1] != '\n')
+		PyFile_WriteString("\n", f);
+	if (offset == -1)
+		return;
+	PyFile_WriteString("    ", f);
+	offset--;
+	while (offset > 0) {
+		PyFile_WriteString(" ", f);
+		offset--;
+	}
+	PyFile_WriteString("^\n", f);
+}
+
 void
 PyErr_PrintEx(int set_sys_last_vars)
 {
@@ -795,36 +835,8 @@ PyErr_PrintEx(int set_sys_last_vars)
 				sprintf(buf, "%d", lineno);
 				PyFile_WriteString(buf, f);
 				PyFile_WriteString("\n", f);
-				if (text != NULL) {
-					char *nl;
-					if (offset > 0 &&
-					    offset == (int)strlen(text))
-						offset--;
-					for (;;) {
-						nl = strchr(text, '\n');
-						if (nl == NULL ||
-						    nl-text >= offset)
-							break;
-						offset -= (nl+1-text);
-						text = nl+1;
-					}
-					while (*text == ' ' || *text == '\t') {
-						text++;
-						offset--;
-					}
-					PyFile_WriteString("    ", f);
-					PyFile_WriteString(text, f);
-					if (*text == '\0' ||
-					    text[strlen(text)-1] != '\n')
-						PyFile_WriteString("\n", f);
-					PyFile_WriteString("    ", f);
-					offset--;
-					while (offset > 0) {
-						PyFile_WriteString(" ", f);
-						offset--;
-					}
-					PyFile_WriteString("^\n", f);
-				}
+				if (text != NULL)
+					print_error_text(f, offset, text);
 				Py_INCREF(message);
 				Py_DECREF(v);
 				v = message;