lib: various documentation fixes

 - Consistently use nullable instead of `type|null` expressions
 - Use @borrows to reduce some duplicated documentation blocks
 - Add typedef for timelocal()/timegm() TimeSpec value

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

3 files changed, 112 insertions, 153 deletions

diff --git a/lib.c b/lib.c
index d23dde2..726a74d 100644
--- a/lib.c
+++ b/lib.c
@@ -365,7 +365,7 @@ uc_print(uc_vm_t *vm, size_t nargs)
  *
  * @param {Object|Array|string} x - The input object, array, or string.
  *
- * @returns {number|null} - The length of the input.
+ * @returns {?number} - The length of the input.
  *
  * @example
  * length("test")                             // 4
@@ -484,7 +484,7 @@ uc_index(uc_vm_t *vm, size_t nargs, bool right)
  * @param {*} needle
  * The value to find within the array or string.
  *
- * @returns {number|null}
+ * @returns {?number}
  *
  * @example
  * index("Hello hello hello", "ll")          // 2
@@ -516,7 +516,7 @@ uc_lindex(uc_vm_t *vm, size_t nargs)
  * @param {*} needle
  * The value to find within the array or string.
  *
- * @returns {number|null}
+ * @returns {?number}
  *
  * @example
  * rindex("Hello hello hello", "ll")          // 14
@@ -844,7 +844,7 @@ uc_exit(uc_vm_t *vm, size_t nargs)
  * @param {string} [name]
  * The name of the environment variable.
  *
- * @returns {string|object}
+ * @returns {string|Object<string, string>}
  */
 static uc_value_t *
 uc_getenv(uc_vm_t *vm, size_t nargs)
@@ -1037,7 +1037,7 @@ uc_int(uc_vm_t *vm, size_t nargs)
  * @param {Array} arr
  * The array to be joined into a string.
  *
- * @returns {string|null}
+ * @returns {?string}
  */
 static uc_value_t *
 uc_join(uc_vm_t *vm, size_t nargs)
@@ -1073,7 +1073,7 @@ uc_join(uc_vm_t *vm, size_t nargs)
  * @param {object} obj
  * The object from which to retrieve the key names.
  *
- * @returns {Array|null}
+ * @returns {?Array}
  */
 static uc_value_t *
 uc_keys(uc_vm_t *vm, size_t nargs)
@@ -1104,7 +1104,7 @@ uc_keys(uc_vm_t *vm, size_t nargs)
  * @param {string} s
  * The input string.
  *
- * @returns {string|null}
+ * @returns {?string}
  * The lowercase string.
  *
  * @example
@@ -1211,7 +1211,7 @@ uc_map(uc_vm_t *vm, size_t nargs)
  * @param {number} [offset]
  * The offset of the character.
  *
- * @returns {number|null}
+ * @returns {?number}
  *
  * @example
  * ord("Abc");         // 65
@@ -1265,7 +1265,7 @@ uc_ord(uc_vm_t *vm, size_t nargs)
  * @param {*} x
  * The value to determine the type of.
  *
- * @returns {string|null}
+ * @returns {?string}
  */
 static uc_value_t *
 uc_type(uc_vm_t *vm, size_t nargs)
@@ -1307,7 +1307,7 @@ uc_type(uc_vm_t *vm, size_t nargs)
  * @param {Array|string} arr_or_str
  * The input array or string.
  *
- * @returns {Array|string|null}
+ * @returns {?(Array|string)}
  *
  * @example
  * reverse([1, 2, 3]);   // [ 3, 2, 1 ]
@@ -1938,7 +1938,7 @@ uc_time(uc_vm_t *vm, size_t nargs)
  * @param {*} str
  * The string to be converted to uppercase.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * uc("hello");   // "HELLO"
@@ -2040,7 +2040,7 @@ uc_uchr(uc_vm_t *vm, size_t nargs)
  * @param {*} obj
  * The object from which to extract values.
  *
- * @returns {Array|null}
+ * @returns {?Array}
  *
  * @example
  * values({ foo: true, bar: false });   // [true, false]
@@ -2774,7 +2774,7 @@ uc_require(uc_vm_t *vm, size_t nargs)
  * @param {string} address
  * The IP address string to convert.
  *
- * @returns {number[]|null}
+ * @returns {?number[]}
  *
  * @example
  * iptoarr("192.168.1.1")              // [ 192, 168, 1, 1 ]
@@ -2851,7 +2851,7 @@ check_byte(uc_value_t *v)
  * @param {number[]} arr
  * The byte array to convert into an IP address string.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * arrtoip([ 192, 168, 1, 1 ])   // "192.168.1.1"
@@ -2928,7 +2928,7 @@ uc_arrtoip(uc_vm_t *vm, size_t nargs)
  * @param {RegExp} pattern
  * The regular expression pattern.
  *
- * @returns {Array|null}
+ * @returns {?Array}
  *
  * @example
  * match("foobarbaz", /b.(.)/)   // ["bar", "r"]
@@ -3976,7 +3976,7 @@ uc_trace(uc_vm_t *vm, size_t nargs)
  * @param {Object} [proto]
  * The optional prototype object.
  *
- * @returns {Object|null}
+ * @returns {?Object}
  *
  * @example
  * const arr = [1, 2, 3];
@@ -4222,7 +4222,7 @@ uc_wildcard(uc_vm_t *vm, size_t nargs)
  * @param {boolean} [dironly]
  * Whether to return only the directory portion of the source file path.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * sourcepath();         // Returns the path of the currently executed file
@@ -4426,7 +4426,7 @@ uc_max(uc_vm_t *vm, size_t nargs)
  * @param {string} str
  * The base64 encoded string to decode.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * b64dec("VGhpcyBpcyBhIHRlc3Q=");         // Returns "This is a test"
@@ -4576,7 +4576,7 @@ static const char Base64[] =
  * @param {string} str
  * The string to encode.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * b64enc("This is a test");  // Returns "VGhpcyBpcyBhIHRlc3Q="
@@ -4713,7 +4713,7 @@ uc_uniq_ucv_equal(const void *k1, const void *k2)
  * @param {Array} array
  * The input array.
  *
- * @returns {Array|null}
+ * @returns {?Array}
  *
  * @example
  * uniq([1, true, "foo", 2, true, "bar", "foo"]);       // Returns [1, true, "foo", 2, "bar"]
@@ -4752,6 +4752,28 @@ uc_uniq(uc_vm_t *vm, size_t nargs)
 	return uniq;
 }
 
+/**
+ * A time spec is a plain object describing a point in time, it is returned by
+ * the {@link module:core#gmtime|gmtime()} and
+ * {@link module:core#localtime|localtime()} functions and expected as parameter
+ * by the complementary {@link module:core#timegm|timegm()} and
+ * {@link module:core#timelocal|timelocal()} functions.
+ *
+ * When returned by `gmtime()` or `localtime()`, all members of the object will
+ * be initialized, when passed as argument to `timegm()` or `timelocal()`, most
+ * member values are optional.
+ *
+ * @typedef {Object} module:core.TimeSpec
+ * @property {number} sec - Seconds (0..60)
+ * @property {number} min - Minutes (0..59)
+ * @property {number} hour - Hours (0..23)
+ * @property {number} mday - Day of month (1..31)
+ * @property {number} mon - Month (1..12)
+ * @property {number} year - Year (>= 1900)
+ * @property {number} wday - Day of week (1..7, Sunday = 7)
+ * @property {number} yday - Day of year (1-366, Jan 1st = 1)
+ * @property {number} isdst - Daylight saving time in effect (yes = 1)
+ */
 static uc_value_t *
 uc_gettime_common(uc_vm_t *vm, size_t nargs, bool local)
 {
@@ -4782,16 +4804,7 @@ uc_gettime_common(uc_vm_t *vm, size_t nargs, bool local)
  * containing broken-down date and time information according to the local
  * system timezone.
  *
- * The resulting dictionary contains the following fields:
- * - `sec`    Seconds (0-60)
- * - `min`    Minutes (0-59)
- * - `hour`   Hours (0-23)
- * - `mday`   Day of month (1-31)
- * - `mon`    Month (1-12)
- * - `year`   Year (>= 1900)
- * - `wday`   Day of the week (1-7, Sunday = 7)
- * - `yday`   Day of the year (1-366, Jan 1st = 1)
- * - `isdst`  Daylight saving time in effect (yes = 1)
+ * See {@link module:core.TimeSpec|TimeSpec} for a description of the fields.
  *
  * Note that in contrast to the underlying `localtime(3)` C library function,
  * the values for `mon`, `wday`, and `yday` are 1-based, and the `year` is
@@ -4802,7 +4815,7 @@ uc_gettime_common(uc_vm_t *vm, size_t nargs, bool local)
  * @param {number} [epoch]
  * The epoch timestamp.
  *
- * @returns {Object}
+ * @returns {module:core.TimeSpec}
  *
  * @example
  * localtime(1647953502);
@@ -4828,14 +4841,14 @@ uc_localtime(uc_vm_t *vm, size_t nargs)
 /**
  * Like `localtime()` but interpreting the given epoch value as UTC time.
  *
- * See `localtime()` for details on the return value.
+ * See {@link module:core#localtime|localtime()} for details on the return value.
  *
  * @function module:core#gmtime
  *
  * @param {number} [epoch]
  * The epoch timestamp.
  *
- * @returns {Object}
+ * @returns {module:core.TimeSpec}
  *
  * @example
  * gmtime(1647953502);
@@ -4908,9 +4921,9 @@ uc_mktime_common(uc_vm_t *vm, size_t nargs, bool local)
 }
 
 /**
- * Performs the inverse operation of `localtime()` by taking a broken-down date
- * and time dictionary and transforming it into an epoch value according to the
- * local system timezone.
+ * Performs the inverse operation of {@link module:core#localtime|localtime()}
+ * by taking a broken-down date and time dictionary and transforming it into an
+ * epoch value according to the local system timezone.
  *
  * The `wday` and `yday` fields of the given date time specification are
  * ignored. Field values outside of their valid range are internally normalized,
@@ -4922,10 +4935,10 @@ uc_mktime_common(uc_vm_t *vm, size_t nargs, bool local)
  *
  * @function module:core#timelocal
  *
- * @param {Object} datetimespec
+ * @param {module:core.TimeSpec} datetimespec
  * The broken-down date and time dictionary.
  *
- * @returns {number|null}
+ * @returns {?number}
  *
  * @example
  * timelocal({ "sec": 42, "min": 51, "hour": 13, "mday": 22, "mon": 3, "year": 2022, "isdst": 0 });
@@ -4941,14 +4954,14 @@ uc_timelocal(uc_vm_t *vm, size_t nargs)
  * Like `timelocal()` but interpreting the given date time specification as UTC
  * time.
  *
- * See `timelocal()` for details.
+ * See {@link module:core#timelocal|timelocal()} for details.
  *
  * @function module:core#timegm
  *
- * @param {Object} datetimespec
+ * @param {module:core.TimeSpec} datetimespec
  * The broken-down date and time dictionary.
  *
- * @returns {number|null}
+ * @returns {?number}
  *
  * @example
  * timegm({ "sec": 42, "min": 51, "hour": 13, "mday": 22, "mon": 3, "year": 2022, "isdst": 0 });
@@ -4980,7 +4993,7 @@ uc_timegm(uc_vm_t *vm, size_t nargs)
  * @param {boolean} [monotonic]
  * Whether to query the monotonic system clock.
  *
- * @returns {Array<number>|null}
+ * @returns {?number[]}
  *
  * @example
  * clock();        // [ 1647954926, 798269464 ]
@@ -5078,7 +5091,7 @@ hexval(unsigned char c, bool lo)
  * @param {string} [skipchars]
  * The characters to skip during decoding.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * hexdec("48656c6c6f20776f726c64210a");  // "Hello world!\n"
@@ -5165,7 +5178,7 @@ uc_hexdec(uc_vm_t *vm, size_t nargs)
  * @param {*} [argument]
  * The argument for the operation.
  *
- * @returns {boolean|number|null}
+ * @returns {?(boolean|number)}
  *
  * @example
  * gc();         // true
diff --git a/lib/debug.c b/lib/debug.c
index 40b044e..0b227d9 100644
--- a/lib/debug.c
+++ b/lib/debug.c
@@ -667,7 +667,7 @@ debug_setup(uc_vm_t *vm)
  * @param {string|module:fs.file|module:fs.proc} file
  * The file path or open file handle to write report to.
  *
- * @return {boolean|null}
+ * @return {?boolean}
  */
 static uc_value_t *
 uc_memdump(uc_vm_t *vm, size_t nargs)
@@ -818,7 +818,7 @@ uc_traceback(uc_vm_t *vm, size_t nargs)
  *
  * @function module:debug#sourcepos
  *
- * @return {module:debug.SourcePosition|null}
+ * @return {?module:debug.SourcePosition}
  */
 
 /**
@@ -955,7 +955,7 @@ uc_getinfo_upvals(uc_vm_t *vm, uc_closure_t *closure)
  * @param {*} value
  * The value to query information for.
  *
- * @return {module:debug.ValueInformation|null}
+ * @return {?module:debug.ValueInformation}
  */
 
 /**
@@ -1362,7 +1362,7 @@ uc_xlocal(uc_vm_t *vm, uc_value_t *level, uc_value_t *var, uc_value_t **set)
  * @param {string|number} variable
  * The variable index or variable name to obtain information for.
  *
- * @returns {module:debug.LocalInfo|null}
+ * @returns {?module:debug.LocalInfo}
  */
 static uc_value_t *
 uc_getlocal(uc_vm_t *vm, size_t nargs)
@@ -1406,7 +1406,7 @@ uc_getlocal(uc_vm_t *vm, size_t nargs)
  * @param {*} [value=null]
  * The value to set the local variable to.
  *
- * @returns {module:debug.LocalInfo|null}
+ * @returns {?module:debug.LocalInfo}
  */
 static uc_value_t *
 uc_setlocal(uc_vm_t *vm, size_t nargs)
@@ -1552,7 +1552,7 @@ uc_xupval(uc_vm_t *vm, uc_value_t *target, uc_value_t *var, uc_value_t **set)
  * @param {string|number} variable
  * The variable index or variable name to obtain information for.
  *
- * @returns {module:debug.UpvalInfo|null}
+ * @returns {?module:debug.UpvalInfo}
  */
 static uc_value_t *
 uc_getupval(uc_vm_t *vm, size_t nargs)
@@ -1601,7 +1601,7 @@ uc_getupval(uc_vm_t *vm, size_t nargs)
  * @param {*} value
  * The value to set the variable to.
  *
- * @returns {module:debug.UpvalInfo|null}
+ * @returns {?module:debug.UpvalInfo}
  */
 static uc_value_t *
 uc_setupval(uc_vm_t *vm, size_t nargs)
diff --git a/lib/fs.c b/lib/fs.c
index 0f03ad4..4d9695e 100644
--- a/lib/fs.c
+++ b/lib/fs.c
@@ -79,7 +79,7 @@ static int last_error = 0;
  * @function module:fs#error
  *
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * // Trigger file system error
@@ -258,6 +258,8 @@ uc_fs_fileno_common(uc_vm_t *vm, size_t nargs, const char *type)
  * @class module:fs.proc
  * @hideconstructor
  *
+ * @borrows module:fs#error as module:fs.proc#error
+ *
  * @see {@link module:fs#popen|popen()}
  *
  * @example
@@ -276,26 +278,6 @@ uc_fs_fileno_common(uc_vm_t *vm, size_t nargs, const char *type)
  */
 
 /**
- * Query error information.
- *
- * Returns a string containing a description of the last occurred error or
- * `null` if there is no error information.
- *
- * @function module:fs.proc#error
- *
- * @returns {string|null}
- *
- * @example
- * // Trigger error
- * const fp = popen("command");
- * fp.close();
- * fp.close(); // already closed
- *
- * // Print error (should yield "Bad file descriptor")
- * print(fp.error(), "\n");
- */
-
-/**
  * Closes the program handle and awaits program termination.
  *
  * Upon calling `close()` on the handle, the program's input or output stream
@@ -316,7 +298,7 @@ uc_fs_fileno_common(uc_vm_t *vm, size_t nargs, const char *type)
  *
  * @function module:fs.proc#close
  *
- * @returns {number|null}
+ * @returns {?number}
  */
 static uc_value_t *
 uc_fs_pclose(uc_vm_t *vm, size_t nargs)
@@ -378,7 +360,7 @@ uc_fs_pclose(uc_vm_t *vm, size_t nargs)
  * The length of data to read. Can be a number, the string "line", the string
  * "all", or a single character string.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * const fp = popen("command", "r");
@@ -426,7 +408,7 @@ uc_fs_pread(uc_vm_t *vm, size_t nargs)
  * @param {*} data
  * The data to be written.
  *
- * @returns {number|null}
+ * @returns {?number}
  *
  * @example
  * const fp = popen("command", "w");
@@ -448,7 +430,7 @@ uc_fs_pwrite(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.proc#flush
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  */
 static uc_value_t *
@@ -466,7 +448,7 @@ uc_fs_pflush(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.proc#fileno
  *
- * @returns {number|null}
+ * @returns {?number}
  */
 static uc_value_t *
 uc_fs_pfileno(uc_vm_t *vm, size_t nargs)
@@ -498,7 +480,7 @@ uc_fs_pfileno(uc_vm_t *vm, size_t nargs)
  * @param {string} [mode="r"]
  * The open mode of the process handle.
  *
- * @returns {module:fs.proc|null}
+ * @returns {?module:fs.proc}
  *
  * @example
  * // Open a process
@@ -531,6 +513,8 @@ uc_fs_popen(uc_vm_t *vm, size_t nargs)
  * @class module:fs.file
  * @hideconstructor
  *
+ * @borrows module:fs#error as module:fs.file#error
+ *
  * @see {@link module:fs#open|open()}
  * @see {@link module:fs#fdopen|fdopen()}
  * @see {@link module:fs#mkstemp|mkstemp()}
@@ -556,26 +540,6 @@ uc_fs_popen(uc_vm_t *vm, size_t nargs)
  */
 
 /**
- * Query error information.
- *
- * Returns a string containing a description of the last occurred error or
- * `null` if there is no error information.
- *
- * @function module:fs.file#error
- *
- * @returns {string|null}
- *
- * @example
- * // Trigger error
- * const fp = open("file.txt");
- * fp.close();
- * fp.close(); // already closed
- *
- * // Print error (should yield "Bad file descriptor")
- * print(fp.error(), "\n");
- */
-
-/**
  * Closes the file handle.
  *
  * Upon calling `close()` on the handle, buffered data is flushed and the
@@ -587,7 +551,7 @@ uc_fs_popen(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.file#close
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  */
 static uc_value_t *
 uc_fs_close(uc_vm_t *vm, size_t nargs)
@@ -639,7 +603,7 @@ uc_fs_close(uc_vm_t *vm, size_t nargs)
  * The length of data to read. Can be a number, the string "line", the string
  * "all", or a single character string.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * const fp = open("file.txt", "r");
@@ -687,7 +651,7 @@ uc_fs_read(uc_vm_t *vm, size_t nargs)
  * @param {*} data
  * The data to be written.
  *
- * @returns {number|null}
+ * @returns {?number}
  *
  * @example
  * const fp = open("file.txt", "w");
@@ -724,7 +688,7 @@ uc_fs_write(uc_vm_t *vm, size_t nargs)
  * | `1`      | The given offset is relative to the current read position.                                   |
  * | `2`      | The given offset is relative to the end of the file.                                         |
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * const fp = open("file.txt", "r");
@@ -785,7 +749,7 @@ uc_fs_seek(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.file#tell
  *
- * @returns {number|null}
+ * @returns {?number}
  */
 static uc_value_t *
 uc_fs_tell(uc_vm_t *vm, size_t nargs)
@@ -818,7 +782,7 @@ uc_fs_tell(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.file#isatty
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  */
 static uc_value_t *
@@ -847,7 +811,7 @@ uc_fs_isatty(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.file#flush
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  */
 static uc_value_t *
@@ -865,7 +829,7 @@ uc_fs_flush(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.file#fileno
  *
- * @returns {number|null}
+ * @returns {?number}
  */
 static uc_value_t *
 uc_fs_fileno(uc_vm_t *vm, size_t nargs)
@@ -913,7 +877,7 @@ uc_fs_fileno(uc_vm_t *vm, size_t nargs)
  * @param {number} [perm=0o666]
  * The file creation permissions (for modes `w…` and `a…`)
  *
- * @returns {module:fs.file|null}
+ * @returns {?module:fs.file}
  *
  * @example
  * // Open a file in read-only mode
@@ -1058,6 +1022,8 @@ uc_fs_fdopen(uc_vm_t *vm, size_t nargs)
  * @class module:fs.dir
  * @hideconstructor
  *
+ * @borrows module:fs#error as module:fs.dir#error
+ *
  * @see {@link module:fs#opendir|opendir()}
  *
  * @example
@@ -1075,26 +1041,6 @@ uc_fs_fdopen(uc_vm_t *vm, size_t nargs)
  */
 
 /**
- * Query error information.
- *
- * Returns a string containing a description of the last occurred error or
- * `null` if there is no error information.
- *
- * @function module:fs.dir#error
- *
- * @returns {string|null}
- *
- * @example
- * // Trigger error
- * const fp = opendir("/tmp");
- * fp.close();
- * fp.close(); // already closed
- *
- * // Print error (should yield "Bad file descriptor")
- * print(fp.error(), "\n");
- */
-
-/**
  * Read the next entry from the open directory.
  *
  * Returns a string containing the entry name.
@@ -1105,7 +1051,7 @@ uc_fs_fdopen(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.dir#read
  *
- * @returns {string|null}
+ * @returns {?string}
  */
 static uc_value_t *
 uc_fs_readdir(uc_vm_t *vm, size_t nargs)
@@ -1139,7 +1085,7 @@ uc_fs_readdir(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.dir#tell
  *
- * @returns {number|null}
+ * @returns {?number}
  */
 static uc_value_t *
 uc_fs_telldir(uc_vm_t *vm, size_t nargs)
@@ -1174,7 +1120,7 @@ uc_fs_telldir(uc_vm_t *vm, size_t nargs)
  * @param {number} offset
  * Position value obtained by `tell()`.
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  *
@@ -1218,7 +1164,7 @@ uc_fs_seekdir(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs.dir#close
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  */
 static uc_value_t *
 uc_fs_closedir(uc_vm_t *vm, size_t nargs)
@@ -1247,7 +1193,7 @@ uc_fs_closedir(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to the directory.
  *
- * @returns {module:fs.dir|null}
+ * @returns {?module:fs.dir}
  *
  * @example
  * // Open a directory
@@ -1282,7 +1228,7 @@ uc_fs_opendir(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to the symbolic link.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * // Read the value of a symbolic link
@@ -1456,7 +1402,7 @@ uc_fs_stat_common(uc_vm_t *vm, size_t nargs, bool use_lstat)
  * @param {string} path
  * The path to the file or directory.
  *
- * @returns {module:fs.FileStatResult|null}
+ * @returns {?module:fs.FileStatResult}
  *
  * @example
  * // Get information about a file
@@ -1481,7 +1427,7 @@ uc_fs_stat(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to the file or directory.
  *
- * @returns {module:fs.FileStatResult|null}
+ * @returns {?module:fs.FileStatResult}
  *
  * @example
  * // Get information about a directory
@@ -1505,7 +1451,7 @@ uc_fs_lstat(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to the new directory.
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * // Create a directory
@@ -1539,7 +1485,7 @@ uc_fs_mkdir(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to the directory to be removed.
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * // Remove a directory
@@ -1574,7 +1520,7 @@ uc_fs_rmdir(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path of the symbolic link.
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * // Create a symbolic link
@@ -1608,7 +1554,7 @@ uc_fs_symlink(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to the file or symbolic link.
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * // Remove a file
@@ -1637,7 +1583,7 @@ uc_fs_unlink(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs#getcwd
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * // Get the current working directory
@@ -1692,7 +1638,7 @@ uc_fs_getcwd(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to the new working directory.
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * // Change the current working directory
@@ -1728,7 +1674,7 @@ uc_fs_chdir(uc_vm_t *vm, size_t nargs)
  * @param {number} mode
  * The new mode (permissions).
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * // Change the mode of a file
@@ -1872,7 +1818,7 @@ uc_fs_resolve_group(uc_value_t *v, gid_t *gid)
  * The new group's ID. When given as number, it is used as-is, when given as
  * string, the group name is resolved to the corresponding gid first.
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * // Change the owner of a file
@@ -1918,7 +1864,7 @@ uc_fs_chown(uc_vm_t *vm, size_t nargs)
  * @param {string} newPath
  * The new path of the file or directory.
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * // Rename a file
@@ -1980,7 +1926,7 @@ uc_fs_glob(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to extract the directory name from.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * // Get the directory name of a path
@@ -2029,7 +1975,7 @@ uc_fs_dirname(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to extract the base name from.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * // Get the base name of a path
@@ -2083,7 +2029,7 @@ uc_fs_lsdir_sort_fn(const void *k1, const void *k2)
  * @param {string} path
  * The path to the directory.
  *
- * @returns {string[]|null}
+ * @returns {?string[]}
  *
  * @example
  * // List the content of a directory
@@ -2169,7 +2115,7 @@ uc_fs_lsdir(uc_vm_t *vm, size_t nargs)
  * @param {string} [template="/tmp/XXXXXX"]
  * The path template to use when forming the temporary file name.
  *
- * @returns {module:fs.file|null}
+ * @returns {?module:fs.file}
  *
  * @example
  * // Create a unique temporary file in the current working directory
@@ -2261,7 +2207,7 @@ uc_fs_mkstemp(uc_vm_t *vm, size_t nargs)
  * @param {number} [mode="f"]
  * Optional access mode.
  *
- * @returns {boolean|null}
+ * @returns {?boolean}
  *
  * @example
  * // Check file read and write accessibility
@@ -2329,7 +2275,7 @@ uc_fs_access(uc_vm_t *vm, size_t nargs)
  * Number of bytes to limit the result to. When omitted, the entire content is
  * returned.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * // Read first 100 bytes of content
@@ -2441,7 +2387,7 @@ uc_fs_readfile(uc_vm_t *vm, size_t nargs)
  * Truncates the amount of data to be written to the specified amount of bytes.
  * When omitted, the entire content is written.
  *
- * @returns {number|null}
+ * @returns {?number}
  *
  * @example
  * // Write string to a file
@@ -2522,7 +2468,7 @@ uc_fs_writefile(uc_vm_t *vm, size_t nargs)
  * @param {string} path
  * The path to the file or directory.
  *
- * @returns {string|null}
+ * @returns {?string}
  *
  * @example
  * // Resolve the absolute path of a file
@@ -2561,7 +2507,7 @@ uc_fs_realpath(uc_vm_t *vm, size_t nargs)
  *
  * @function module:fs#pipe
  *
- * @returns {module:fs.file[]|null}
+ * @returns {?module:fs.file[]}
  *
  * @example
  * // Create a pipe