Add py.unchecked for casting PyObject to Pydust class (#230)

TODO(ngates): we should store PyType objects on module state and then
auto-traverse them. See #229

Fixes #226, #227, #228

pydust/src/conversions.zig

@@ -12,6 +12,8 @@
 
 const py = @import("./pydust.zig");
 const tramp = @import("./trampoline.zig");
+const pytypes = @import("./pytypes.zig");
+const State = @import("./discovery.zig").State;
 
 /// Zig PyObject-like -> ffi.PyObject. Convert a Zig PyObject-like value into a py.PyObject.
 ///  e.g. py.PyObject, py.PyTuple, ffi.PyObject, etc.
@@ -38,6 +40,30 @@ pub inline fn as(comptime T: type, obj: anytype) py.PyError!T {
     return tramp.Trampoline(T).unwrap(object(obj));
 }
 
+/// Python -> Pydust. Perform a checked cast from a PyObject to a given PyDust class type.
+pub inline fn checked(comptime T: type, obj: py.PyObject) py.PyError!T {
+    const definition = State.getDefinition(@typeInfo(T).Pointer.child);
+    if (definition.type != .class) {
+        @compileError("Can only perform checked cast into a PyDust class type");
+    }
+
+    // TODO(ngates): to perform fast type checking, we need to store our PyType on the parent module.
+    // See how the Python JSON module did this: https://github.com/python/cpython/commit/33f15a16d40cb8010a8c758952cbf88d7912ee2d#diff-efe183ae0b85e5b8d9bbbc588452dd4de80b39fd5c5174ee499ba554217a39edR1814
+    // For now, we perform a slow import/isinstance check by using the `as` conversion.
+    return as(T, obj);
+}
+
+/// Python -> Pydust. Perform an unchecked cast from a PyObject to a given PyDust class type.
+pub inline fn unchecked(comptime T: type, obj: py.PyObject) T {
+    const Definition = @typeInfo(T).Pointer.child;
+    const definition = State.getDefinition(Definition);
+    if (definition.type != .class) {
+        @compileError("Can only perform unchecked cast into a PyDust class type. Found " ++ @typeName(Definition));
+    }
+    const instance: *pytypes.PyTypeStruct(Definition) = @ptrCast(@alignCast(obj.py));
+    return &instance.state;
+}
+
 const testing = @import("std").testing;
 const expect = testing.expect;
 

pydust/src/functions.zig

@@ -33,6 +33,13 @@ pub const Signature = struct {
     pub fn supportsKwargs(comptime self: @This()) bool {
         return self.nkwargs > 0 or self.varkwargsIdx != null;
     }
+
+    pub fn isModuleMethod(comptime self: @This()) bool {
+        if (self.selfParam) |Self| {
+            return State.getDefinition(@typeInfo(Self).Pointer.child).type == .module;
+        }
+        return false;
+    }
 };
 
 pub const BinaryOperators = std.ComptimeStringMap(c_int, .{
@@ -257,7 +264,8 @@ pub fn wrap(comptime definition: type, comptime func: anytype, comptime sig: Sig
         }
 
         inline fn internal(pyself: py.PyObject, pyargs: []py.PyObject) PyError!py.PyObject {
-            const self = if (sig.selfParam) |Self| try py.as(Self, pyself) else null;
+            const self = if (sig.selfParam) |Self| try castSelf(Self, pyself) else null;
+
             if (sig.argsParam) |Args| {
                 const args = try unwrapArgs(Args, pyargs, py.Kwargs.init(py.allocator));
                 const result = if (sig.selfParam) |_| func(self, args) else func(args);
@@ -302,10 +310,19 @@ pub fn wrap(comptime definition: type, comptime func: anytype, comptime sig: Sig
             pykwargs: py.Kwargs,
         ) PyError!py.PyObject {
             const args = try unwrapArgs(sig.argsParam.?, pyargs, pykwargs);
-            const self = if (sig.selfParam) |Self| try py.as(Self, pyself) else null;
+            const self = if (sig.selfParam) |Self| try castSelf(Self, pyself) else null;
             const result = if (sig.selfParam) |_| func(self, args) else func(args);
             return py.createOwned(tramp.coerceError(result));
         }
+
+        inline fn castSelf(comptime Self: type, pyself: py.PyObject) !Self {
+            if (comptime sig.isModuleMethod()) {
+                const mod = py.PyModule{ .obj = pyself };
+                return try mod.getState(@typeInfo(Self).Pointer.child);
+            } else {
+                return py.unchecked(Self, pyself);
+            }
+        }
     };
 }
 

pydust/src/pytypes.zig

@@ -666,7 +666,7 @@ fn RichCompare(comptime definition: type) type {
             const CompareOpArg = typeInfo.params[2].type.?;
             if (CompareOpArg != py.CompareOp) @compileError("Third parameter of __richcompare__ must be a py.CompareOp");
 
-            const self = py.as(Self, pyself) catch return null;
+            const self = py.unchecked(Self, .{ .py = pyself });
             const otherArg = tramp.Trampoline(Other).unwrap(.{ .py = pyother }) catch return null;
             const opEnum: py.CompareOp = @enumFromInt(op);
 

pydust/src/types/module.zig

@@ -31,7 +31,7 @@ pub const PyModule = extern struct {
         return .{ .obj = .{ .py = ffi.PyImport_ImportModule(name) orelse return PyError.PyRaised } };
     }
 
-    pub fn getState(self: PyModule, comptime state: type) !*state {
+    pub fn getState(self: PyModule, comptime ModState: type) !*ModState {
         const statePtr = ffi.PyModule_GetState(self.obj.py) orelse return PyError.PyRaised;
         return @ptrCast(@alignCast(statePtr));
     }