subscriber: clarify the provenance of fmt/time/datetime.rs (#1712)

Add comments to clarify the provenance of `fmt/time/datetime.rs`,
addressing #1644.

Fixes #1644

tracing-subscriber/src/fmt/time/datetime.rs

@@ -1,19 +1,214 @@
+// musl as a whole is licensed under the following standard MIT license:
+//
+// ----------------------------------------------------------------------
+// Copyright © 2005-2020 Rich Felker, et al.
+//
+// Permission is hereby granted, free of charge, to any person obtaining
+// a copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to
+// permit persons to whom the Software is furnished to do so, subject to
+// the following conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+// ----------------------------------------------------------------------
+//
+// Authors/contributors include:
+//
+// A. Wilcox
+// Ada Worcester
+// Alex Dowad
+// Alex Suykov
+// Alexander Monakov
+// Andre McCurdy
+// Andrew Kelley
+// Anthony G. Basile
+// Aric Belsito
+// Arvid Picciani
+// Bartosz Brachaczek
+// Benjamin Peterson
+// Bobby Bingham
+// Boris Brezillon
+// Brent Cook
+// Chris Spiegel
+// Clément Vasseur
+// Daniel Micay
+// Daniel Sabogal
+// Daurnimator
+// David Carlier
+// David Edelsohn
+// Denys Vlasenko
+// Dmitry Ivanov
+// Dmitry V. Levin
+// Drew DeVault
+// Emil Renner Berthing
+// Fangrui Song
+// Felix Fietkau
+// Felix Janda
+// Gianluca Anzolin
+// Hauke Mehrtens
+// He X
+// Hiltjo Posthuma
+// Isaac Dunham
+// Jaydeep Patil
+// Jens Gustedt
+// Jeremy Huntwork
+// Jo-Philipp Wich
+// Joakim Sindholt
+// John Spencer
+// Julien Ramseier
+// Justin Cormack
+// Kaarle Ritvanen
+// Khem Raj
+// Kylie McClain
+// Leah Neukirchen
+// Luca Barbato
+// Luka Perkov
+// M Farkas-Dyck (Strake)
+// Mahesh Bodapati
+// Markus Wichmann
+// Masanori Ogino
+// Michael Clark
+// Michael Forney
+// Mikhail Kremnyov
+// Natanael Copa
+// Nicholas J. Kain
+// orc
+// Pascal Cuoq
+// Patrick Oppenlander
+// Petr Hosek
+// Petr Skocik
+// Pierre Carrier
+// Reini Urban
+// Rich Felker
+// Richard Pennington
+// Ryan Fairfax
+// Samuel Holland
+// Segev Finer
+// Shiz
+// sin
+// Solar Designer
+// Stefan Kristiansson
+// Stefan O'Rear
+// Szabolcs Nagy
+// Timo Teräs
+// Trutz Behn
+// Valentin Ochs
+// Will Dietz
+// William Haddon
+// William Pitcock
+//
+// Portions of this software are derived from third-party works licensed
+// under terms compatible with the above MIT license:
+//
+// The TRE regular expression implementation (src/regex/reg* and
+// src/regex/tre*) is Copyright © 2001-2008 Ville Laurikari and licensed
+// under a 2-clause BSD license (license text in the source files). The
+// included version has been heavily modified by Rich Felker in 2012, in
+// the interests of size, simplicity, and namespace cleanliness.
+//
+// Much of the math library code (src/math/* and src/complex/*) is
+// Copyright © 1993,2004 Sun Microsystems or
+// Copyright © 2003-2011 David Schultz or
+// Copyright © 2003-2009 Steven G. Kargl or
+// Copyright © 2003-2009 Bruce D. Evans or
+// Copyright © 2008 Stephen L. Moshier or
+// Copyright © 2017-2018 Arm Limited
+// and labelled as such in comments in the individual source files. All
+// have been licensed under extremely permissive terms.
+//
+// The ARM memcpy code (src/string/arm/memcpy.S) is Copyright © 2008
+// The Android Open Source Project and is licensed under a two-clause BSD
+// license. It was taken from Bionic libc, used on Android.
+//
+// The AArch64 memcpy and memset code (src/string/aarch64/*) are
+// Copyright © 1999-2019, Arm Limited.
+//
+// The implementation of DES for crypt (src/crypt/crypt_des.c) is
+// Copyright © 1994 David Burren. It is licensed under a BSD license.
+//
+// The implementation of blowfish crypt (src/crypt/crypt_blowfish.c) was
+// originally written by Solar Designer and placed into the public
+// domain. The code also comes with a fallback permissive license for use
+// in jurisdictions that may not recognize the public domain.
+//
+// The smoothsort implementation (src/stdlib/qsort.c) is Copyright © 2011
+// Valentin Ochs and is licensed under an MIT-style license.
+//
+// The x86_64 port was written by Nicholas J. Kain and is licensed under
+// the standard MIT terms.
+//
+// The mips and microblaze ports were originally written by Richard
+// Pennington for use in the ellcc project. The original code was adapted
+// by Rich Felker for build system and code conventions during upstream
+// integration. It is licensed under the standard MIT terms.
+//
+// The mips64 port was contributed by Imagination Technologies and is
+// licensed under the standard MIT terms.
+//
+// The powerpc port was also originally written by Richard Pennington,
+// and later supplemented and integrated by John Spencer. It is licensed
+// under the standard MIT terms.
+//
+// All other files which have no copyright comments are original works
+// produced specifically for use as part of this library, written either
+// by Rich Felker, the main author of the library, or by one or more
+// contibutors listed above. Details on authorship of individual files
+// can be found in the git version control history of the project. The
+// omission of copyright and license comments in each file is in the
+// interest of source tree size.
+//
+// In addition, permission is hereby granted for all public header files
+// (include/* and arch/*/bits/*) and crt files intended to be linked into
+// applications (crt/*, ldso/dlstart.c, and arch/*/crt_arch.h) to omit
+// the copyright notice and permission notice otherwise required by the
+// license, and to use these files without any requirement of
+// attribution. These files include substantial contributions from:
+//
+// Bobby Bingham
+// John Spencer
+// Nicholas J. Kain
+// Rich Felker
+// Richard Pennington
+// Stefan Kristiansson
+// Szabolcs Nagy
+//
+// all of whom have explicitly granted such permission.
+//
+// This file previously contained text expressing a belief that most of
+// the files covered by the above exception were sufficiently trivial not
+// to be subject to copyright, resulting in confusion over whether it
+// negated the permissions granted in the license. In the spirit of
+// permissive licensing, and of not having licensing issues being an
+// obstacle to adoption, that text has been removed.
+
+
 use std::fmt;
 
 /// A date/time type which exists primarily to convert `SystemTime` timestamps into an ISO 8601
 /// formatted string.
 ///
 /// Yes, this exists. Before you have a heart attack, understand that the meat of this is musl's
-/// [`__secs_to_tm`][1] converted to Rust via [c2rust][2] and then cleaned up by hand. All existing
-/// `strftime`-like APIs I found were unable to handle the full range of timestamps representable
-/// by `SystemTime`, including `strftime` itself, since tm.tm_year is an int.
-///
-/// TODO: figure out how to properly attribute the MIT licensed musl project.
+/// [`__secs_to_tm`][1] converted to Rust via [c2rust][2] and then cleaned up by hand as part of
+/// the [kudu-rs project][3], [released under MIT][4].
 ///
 /// [1] http://git.musl-libc.org/cgit/musl/tree/src/time/__secs_to_tm.c
 /// [2] https://c2rust.com/
+/// [3] https://github.com/danburkert/kudu-rs/blob/c9660067e5f4c1a54143f169b5eeb49446f82e54/src/timestamp.rs#L5-L18
+/// [4] https://github.com/tokio-rs/tracing/issues/1644#issuecomment-963888244
 ///
-/// This is directly copy-pasted from https://github.com/danburkert/kudu-rs/blob/c9660067e5f4c1a54143f169b5eeb49446f82e54/src/timestamp.rs#L5-L18
+/// All existing `strftime`-like APIs I found were unable to handle the full range of timestamps representable
+/// by `SystemTime`, including `strftime` itself, since tm.tm_year is an int.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub(crate) struct DateTime {
     year: i64,