union deserialization

src/srf.zig

@@ -519,6 +519,10 @@ pub const Record = struct {
 
     /// Coerce Record to a type. Does not handle fields with arrays
     pub fn to(self: Record, comptime T: type) !T {
+        const ti = @typeInfo(T);
+
+        switch (ti) {
+            .@"struct" => {
                 // SAFETY: all fields updated below or error is returned
                 var obj: T = undefined;
                 inline for (std.meta.fields(T)) |type_field| {
@@ -537,6 +541,27 @@ pub const Record = struct {
                     }
                 }
                 return obj;
+            },
+            .@"union" => {
+                const active_tag_name = if (@hasDecl(T, "srf_tag_field"))
+                    T.srf_tag_field
+                else
+                    "active_tag";
+                if (self.firstFieldByName(active_tag_name)) |srf_field| {
+                    if (srf_field.value == null or srf_field.value.? != .string)
+                        return error.ActiveTagValueMustBeAString;
+                    const active_tag = srf_field.value.?.string;
+                    inline for (std.meta.fields(T)) |f| {
+                        if (std.mem.eql(u8, active_tag, f.name)) {
+                            return @unionInit(T, f.name, try self.to(f.type));
+                        }
+                    }
+                    return error.ActiveTagDoesNotExist;
+                } else return error.ActiveTagFieldNotFound;
+            },
+            else => @compileError("Deserialization not supported on " ++ @tagName(ti) ++ " types"),
+        }
+        return error.CoercionNotPossible;
     }
 };
 
@@ -1292,7 +1317,7 @@ test "unions" {
         foo: Foo,
         bar: Bar,
 
-        //pub const srf_tag_field = "foobar";
+        // pub const srf_tag_field = "foobar";
     };
 
     const data: []const MixedData = &.{
@@ -1313,6 +1338,15 @@ test "unions" {
         \\
     ;
     try std.testing.expectEqualStrings(expect, compact_from);
+
+    var compact_reader = std.Io.Reader.fixed(expect);
+    const parsed = try parse(&compact_reader, std.testing.allocator, .{});
+    defer parsed.deinit();
+
+    const rec1 = try parsed.records.items[0].to(MixedData);
+    try std.testing.expectEqualDeep(data[0], rec1);
+    const rec2 = try parsed.records.items[1].to(MixedData);
+    try std.testing.expectEqualDeep(data[1], rec2);
 }
 test "compact format length-prefixed string as last field" {
     // When a length-prefixed value is the last field on the line,