add map_entry procedure

base/runtime/core_builtin.odin

@@ -936,6 +936,32 @@ map_upsert :: proc(m: ^$T/map[$K]$V, key: K, value: V, loc := #caller_location)
 	return
 }
 
+/*
+Retrieves a pointer to the key and value for a possibly just inserted entry into the map.
+
+If the `key` was not in the map `m`, an entry is inserted with the zero value and `just_inserted` will be `true`.
+Otherwise the existing entry is left untouched and pointers to its key and value are returned.
+
+If the map has to grow in order to insert the entry and the allocation fails, `err` is set and returned.
+
+If `err` is `nil`, `key_ptr` and `value_ptr` are valid pointers and will not be `nil`.
+
+WARN: User modification of the key pointed at by `key_ptr` should only be done if the new key is equal to (in hash) the old key.
+If that is not the case you will corrupt the map.
+*/
+@(builtin, require_results)
+map_entry :: proc(m: ^$T/map[$K]$V, key: K, loc := #caller_location) -> (key_ptr: ^K, value_ptr: ^V, just_inserted: bool, err: Allocator_Error) {
+	key := key
+	zero: V
+
+	_key_ptr, _value_ptr: rawptr
+	_key_ptr, _value_ptr, just_inserted, err = __dynamic_map_entry((^Raw_Map)(m), map_info(T), &key, &zero, loc)
+
+	key_ptr   = (^K)(_key_ptr)
+	value_ptr = (^V)(_value_ptr)
+	return
+}
+
 
 @builtin
 card :: proc "contextless" (s: $S/bit_set[$E; $U]) -> int {

base/runtime/dynamic_map_internal.odin

@@ -941,6 +941,29 @@ __dynamic_map_set_extra :: proc "odin" (#no_alias m: ^Raw_Map, #no_alias info: ^
 	return nil, rawptr(result)
 }
 
+__dynamic_map_entry :: proc "odin" (#no_alias m: ^Raw_Map, #no_alias info: ^Map_Info, key: rawptr, zero: rawptr, loc := #caller_location) -> (key_ptr: rawptr, value_ptr: rawptr, just_inserted: bool, err: Allocator_Error) {
+	hash := info.key_hasher(key, map_seed(m^))
+
+	if key_ptr, value_ptr = __dynamic_map_get_key_and_value(m, info, hash, key); value_ptr != nil {
+		return
+	}
+
+	has_grown: bool
+	if err, has_grown = __dynamic_map_check_grow(m, info, loc); err != nil {
+		return
+	} else if has_grown {
+		hash = info.key_hasher(key, map_seed(m^))
+	}
+
+	value_ptr = rawptr(map_insert_hash_dynamic(m, info, hash, uintptr(key), uintptr(zero)))
+	assert(value_ptr != nil)
+	key_ptr = rawptr(map_cell_index_dynamic(map_data(m^), info.ks, map_desired_position(m^, hash)))
+
+	m.len += 1
+	just_inserted = true
+	return
+}
+
 
 // IMPORTANT: USED WITHIN THE COMPILER
 @(private)