Add a new exception-signaling mode using enriched return values

Cython/Compiler/ExprNodes.py

@@ -5933,7 +5933,7 @@ class SimpleCallNode(CallNode):
         else:
             self.args = [ arg.analyse_types(env) for arg in self.args ]
             self.analyse_c_function_call(env)
-            if func_type.exception_check == '+' or self.type.is_cyp_class:
+            if func_type.exception_check in ('+', '~') or self.type.is_cyp_class:
                 self.is_temp = True
 
         return self
@@ -6228,7 +6228,7 @@ class SimpleCallNode(CallNode):
 
     def is_c_result_required(self):
         func_type = self.function_type()
-        if not func_type.exception_value or func_type.exception_check == '+':
+        if not func_type.exception_value or func_type.exception_check in ('+', '~'):
             return False  # skip allocation of unused result temp
         return True
 
@@ -6330,10 +6330,14 @@ class SimpleCallNode(CallNode):
                 if exc_val is not None:
                     exc_checks.append("%s == %s" % (self.result(), func_type.return_type.cast_code(exc_val)))
                 if exc_check:
-                    if self.nogil:
-                        exc_checks.append("__Pyx_ErrOccurredWithGIL()")
+                    if exc_check == '~':
+                        assert self.is_temp
+                        exc_checks.append(self.type.error_condition(self.result()))
                     else:
-                        exc_checks.append("PyErr_Occurred()")
+                        if self.nogil:
+                            exc_checks.append("__Pyx_ErrOccurredWithGIL()")
+                        else:
+                            exc_checks.append("PyErr_Occurred()")
             if self.is_temp or exc_checks:
                 rhs = self.c_call_code()
                 if self.result():

Cython/Compiler/Nodes.py

@@ -701,12 +701,16 @@ class CFuncDeclaratorNode(CDeclaratorNode):
             env.add_include_file('new')         # for std::bad_alloc
             env.add_include_file('stdexcept')
             env.add_include_file('typeinfo')    # for std::bad_cast
+        elif self.exception_check == '~':
+            self.cpp_check(env)
+            env.use_utility_code(UtilityCode.load_cached("CheckedResult", "CppSupport.cpp"))
+            return_type = PyrexTypes.CheckedResultType(self.pos, return_type)
         if (return_type.is_pyobject
                 and (self.exception_value or self.exception_check)
                 and self.exception_check != '+'):
             error(self.pos, "Exception clause not allowed for function returning Python object")
         else:
-            if self.exception_value is None and self.exception_check and self.exception_check != '+':
+            if self.exception_value is None and self.exception_check and self.exception_check not in ('+', '~'):
                 # Use an explicit exception return value to speed up exception checks.
                 # Even if it is not declared, we can use the default exception value of the return type,
                 # unless the function is some kind of external function that we do not control.
@@ -2244,14 +2248,17 @@ class FuncDefNode(StatNode, BlockNode):
                         self.entry.qualified_name, 0)
                 assure_gil('error')
                 code.put_unraisable(self.entry.qualified_name)
-            default_retval = return_type.default_value
-            if err_val is None and default_retval:
-                err_val = default_retval
-            if err_val is not None:
-                if err_val != Naming.retval_cname:
-                    code.putln("%s = %s;" % (Naming.retval_cname, err_val))
-            elif not return_type.is_void:
-                code.putln("__Pyx_pretend_to_initialize(&%s);" % Naming.retval_cname)
+            if return_type.is_checked_result:
+                code.putln(return_type.set_error(Naming.retval_cname))
+            else:
+                default_retval = return_type.default_value
+                if err_val is None and default_retval:
+                    err_val = default_retval
+                if err_val is not None:
+                    if err_val != Naming.retval_cname:
+                        code.putln("%s = %s;" % (Naming.retval_cname, err_val))
+                elif not return_type.is_void:
+                    code.putln("__Pyx_pretend_to_initialize(&%s);" % Naming.retval_cname)
 
             if is_getbuffer_slot:
                 assure_gil('error')

Cython/Compiler/Parsing.py

@@ -2986,6 +2986,9 @@ def p_exception_value_clause(s):
             elif s.sy == '*':
                 exc_val = ExprNodes.CharNode(s.position(), value=u'*')
                 s.next()
+        elif s.sy == '~':
+            exc_check = '~'
+            s.next()
         else:
             if s.sy == '?':
                 exc_check = 1

Cython/Compiler/PyrexTypes.py

@@ -264,6 +264,7 @@ class PyrexType(BaseType):
     is_memoryviewslice = 0
     is_pythran_expr = 0
     is_numpy_buffer = 0
+    is_checked_result = 0
     has_attributes = 0
     needs_refcounting = 0
     default_value = ""
@@ -595,6 +596,130 @@ class CTypedefType(BaseType):
         return self.typedef_base_type.can_coerce_from_pyobject(env)
 
 
+class CheckedResultType(BaseType):
+    # Pseudo-type to wrap the return value of c functions in a "CheckedResult"
+
+    is_checked_result = 1
+    is_void = 0
+
+    to_py_utility_code = None
+    from_py_utility_code = None
+
+    subtypes = ['checked_base_type']
+
+    def __init__(self, pos, base_type):
+        if base_type.is_reference:
+            error(pos, "Cannot use 'except ~' exception signaling with functions that return by reference")
+        elif base_type.is_cpp_class:
+            base_type.check_nullary_constructor(pos)
+        self.checked_base_type = base_type
+
+    def invalid_value(self):
+        return self.checked_base_type.invalid_value()
+
+    def resolve(self):
+        return self.checked_base_type.resolve()
+
+    def declaration_code(self, entity_code,
+            for_display = 0, dll_linkage = None, pyrex = 0):
+        checked_code = "CheckedResult<%s>" % self.checked_base_type.declaration_code('')
+        if pyrex or for_display:
+            base_code = checked_code
+        else:
+            base_code = public_decl(checked_code, dll_linkage)
+        return self.base_declaration_code(base_code, entity_code)
+
+    def as_argument_type(self):
+        return self.checked_base_type.as_argument_type()
+
+    def cast_code(self, expr_code):
+        return self.checked_base_type.cast_code(expr_code)
+
+    def specialize(self, values):
+        return self.checked_base_type.specialize(values)
+
+    def __repr__(self):
+        return "<CheckedResult[%s]>" % repr(self.checked_base_type)
+
+    def __str__(self):
+        return str(self.checked_base_type)
+
+    def create_to_py_utility_code(self, env):
+        return self.checked_base_type.create_to_py_utility_code(env)
+
+    def create_from_py_utility_code(self, env):
+        return self.checked_base_type.create_from_py_utility_code(env)
+
+    def to_py_call_code(self, source_code, result_code, result_type, to_py_function=None):
+        return self.checked_base_type.to_py_call_code(
+            source_code, result_code, result_type, to_py_function)
+
+    def from_py_call_code(self, source_code, result_code, error_pos, code,
+                          from_py_function=None, error_condition=None):
+        return self.checked_base_type.from_py_call_code(
+            source_code, result_code, error_pos, code,
+            from_py_function or self.from_py_function,
+            error_condition or self.error_condition(result_code)
+        )
+
+    def overflow_check_binop(self, binop, env, const_rhs=False):
+        return self.checked_base_type.overflow_check_binop(binop, env, const_rhs)
+
+    def error_condition(self, result_code):
+        return "%s.is_error()" % result_code
+
+    def set_error(self, result_code):
+        return "%s.set_error();" % result_code
+
+    def __getattr__(self, name):
+        return getattr(self.checked_base_type, name)
+
+    def py_type_name(self):
+        return self.checked_base_type.py_type_name()
+
+    def can_coerce_to_pyobject(self, env):
+        return self.checked_base_type.can_coerce_to_pyobject(env)
+
+    def can_coerce_from_pyobject(self, env):
+        return self.checked_base_type.can_coerce_from_pyobject(env)
+
+    def generate_incref(self, code, cname, **kwds):
+        self.checked_base_type.generate_incref(code, "%s.result" % cname, **kwds)
+
+    def generate_xincref(self, code, cname, **kwds):
+        self.checked_base_type.generate_xincref(code, "%s.result" % cname, **kwds)
+
+    def generate_decref(self, code, cname, **kwds):
+        self.checked_base_type.generate_decref(code, "%s.result" % cname, **kwds)
+
+    def generate_decref_clear(self, code, cname, **kwds):
+        self.checked_base_type.generate_decref_clear(code, "%s.result" % cname, **kwds)
+
+    def generate_xdecref(self, code, cname, **kwds):
+        self.checked_base_type.generate_xdecref(code, "%s.result" % cname, **kwds)
+
+    def generate_xdecref_clear(self, code, cname, **kwds):
+        self.checked_base_type.generate_xdecref_clear(code, "%s.result" % cname, **kwds)
+
+    def generate_gotref(self, code, cname):
+        self.checked_base_type.generate_gotref(code, "%s.result" % cname)
+
+    def generate_xgotref(self, code, cname):
+        self.checked_base_type.generate_xgotref(code, "%s.result" % cname)
+
+    def generate_giveref(self, code, cname):
+        self.checked_base_type.generate_giveref(code, "%s.result" % cname)
+
+    def generate_xgiveref(self, code, cname):
+        self.checked_base_type.generate_xgiveref(code, "%s.result" % cname)
+
+    def generate_decref_set(self, code, cname, rhs_cname):
+        self.checked_base_type.generate_decref_set(code, "%s.result" % cname, rhs_cname)
+
+    def generate_xdecref_set(self, code, cname, rhs_cname):
+        self.checked_base_type.generate_xdecref_set(code, "%s.result" % cname, rhs_cname)
+
+
 class MemoryViewSliceType(PyrexType):
 
     is_memoryviewslice = 1

Cython/Compiler/TypeInference.py

@@ -532,6 +532,8 @@ def find_spanning_type(type1, type2):
     return result_type
 
 def simply_type(result_type, pos):
+    if result_type.is_checked_result:
+        result_type = result_type.checked_base_type
     if result_type.is_reference:
         result_type = result_type.ref_base_type
     if result_type.is_cv_qualified:

Cython/Utility/CppSupport.cpp

@@ -67,3 +67,40 @@ auto __Pyx_pythran_to_python(T &&value) -> decltype(to_python(
 #else
   #define __PYX_STD_MOVE_IF_SUPPORTED(x) x
 #endif
+
+/////////////// CheckedResult.proto ///////////////
+
+#include <type_traits>
+
+template <typename T, bool = std::is_void<T>::value>
+struct CheckedResult {};
+
+template <typename T>
+class CheckedResult<T, false> {
+  enum Status { Ok, Err };
+
+  private:
+    enum Status status;
+
+  public:
+    T result;
+
+    CheckedResult(const T& value) : status(Ok), result(value) {}
+    CheckedResult() : status(Err) {}
+    operator T() { return result; }
+    void set_error() { status = Err; }
+    bool is_error() { return status == Err; }
+};
+
+template <typename T>
+class CheckedResult<T, true> {
+  enum Status { Ok, Err };
+
+  public:
+    CheckedResult() : status(Ok) {}
+    void set_error() { status = Err; }
+    bool is_error() { return status == Err; }
+
+  private:
+    enum Status status;
+};