Add JSON marshaling library

lib/std/encoding/json_marshal.c3

@@ -0,0 +1,164 @@
+// Copyright (c) 2024 C3 Community. All rights reserved.
+// Use of this source code is governed by the MIT license
+// a copy of which can be found in the LICENSE_STDLIB file.
+
+<*
+ JSON marshaling for structs containing primitive types, enums, and nested structs.
+ Supports: String, int, float, double, bool, enums (always marshaled as enum names), nested structs
+*>
+
+module std::encoding::json;
+import std::core::string;
+
+faultdef UNSUPPORTED_TYPE;
+
+<*
+ Marshal a struct with primitive fields and nested structs to JSON.
+
+ @param allocator: "The allocator to use for the result"
+ @param value: "The struct value to marshal"
+ @require @typekind(value) == STRUCT
+ @return "The JSON string representation"
+*>
+macro String? marshal(Allocator allocator, value)
+{
+    var $Type = $typeof(value);
+
+    DString result = dstring::new_with_capacity(allocator, 32);
+    defer result.free();
+
+    result.append_char('{');
+
+    var $first = true;
+    $foreach $member : $Type.membersof:
+        $if $member.nameof != "":
+            $if !$first:
+                result.append_char(',');
+            $endif
+            $first = false;
+
+            // Add field name (always quoted)
+            result.append_char('"');
+            result.append($member.nameof);
+            result.append(`":`);
+
+            // Add field value using common marshaling logic
+            @pool()
+            {
+                String field_result = tmarshal_value($member.get(value))!;
+                result.append(field_result);
+            };
+        $endif
+    $endforeach
+
+    result.append_char('}');
+    return result.copy_str(allocator);
+}
+
+<*
+ Marshal a struct with primitive fields and nested structs to JSON using the temp allocator.
+
+ @param value: "The struct value to marshal"
+ @require @typekind(value) == STRUCT
+ @return "The JSON string representation"
+*>
+macro String? tmarshal(value) => marshal(tmem, value);
+
+<*
+ Marshal a primitive value to JSON.
+
+ @param allocator: "The allocator to use for the result"
+ @param value: "The value to marshal"
+ @return "The JSON string representation"
+*>
+macro String? marshal_value(Allocator allocator, value)
+{
+    var $Type = $typeof(value);
+
+    $switch $Type.kindof:
+        $case STRUCT:
+            return marshal(allocator, value);
+        $case ARRAY:
+        $case SLICE:
+            return marshal_array(allocator, value);
+        $case SIGNED_INT:
+        $case UNSIGNED_INT:
+            return string::tformat("%d", value);
+        $case FLOAT:
+            return string::tformat("%g", value);
+        $case BOOL:
+            return value ? "true" : "false";
+        $case ENUM:
+            return marshal_enum(value);
+        $default:
+            $if $Type.typeid == String.typeid:
+                return value.tescape(false);
+            $endif
+            return UNSUPPORTED_TYPE?;
+    $endswitch
+}
+
+<*
+ Marshal a primitive value to JSON using the temp allocator.
+
+ @param value: "The value to marshal"
+ @return "The JSON string representation"
+*>
+macro String? tmarshal_value(value) => marshal_value(tmem, value);
+
+<*
+ Marshal an array of primitive values to JSON.
+
+ @param allocator: "The allocator to use for the result"
+ @param array: "The array to marshal"
+ @return "The JSON array string representation"
+*>
+macro String? marshal_array(Allocator allocator, array)
+{
+    DString result = dstring::new_with_capacity(allocator, 32);
+    defer result.free();
+
+    result.append_char('[');
+
+    foreach (i, element : array)
+    {
+        if (i > 0) result.append_char(',');
+
+        // Use common marshaling logic for each element
+        @pool()
+        {
+            String element_result = tmarshal_value(element)!;
+            result.append(element_result);
+        };
+    }
+
+    result.append_char(']');
+    return result.copy_str(allocator);
+}
+
+<*
+ Marshal an array of primitive values to JSON using the temp allocator.
+
+ @param array: "The array to marshal"
+ @return "The JSON array string representation"
+*>
+macro String? tmarshal_array(array) => marshal_array(tmem, array);
+
+<*
+ Marshal an enum value to JSON as a quoted string.
+ Always uses the enum name, regardless of associated values.
+
+ @param enum_value: "The enum value to marshal"
+ @return "The JSON string representation"
+*>
+macro String? marshal_enum(enum_value)
+{
+    var $Type = $typeof(enum_value);
+
+    // Convert enum to ordinal and get the name
+    usz ordinal = types::any_to_enum_ordinal(&enum_value, usz)!!;
+    assert(ordinal < $Type.names.len, "Illegal enum value found, numerical value was %d.", ordinal);
+
+    // Always use enum names for JSON marshaling
+    return $Type.names[ordinal].tescape(false);
+}