Add ZeroTrie, an efficient string-to-int collection

Cargo.toml

@@ -43,6 +43,7 @@ members = [
     "experimental/relativetime",
     "experimental/relativetime/data",
     "experimental/unicodeset_parser",
+    "experimental/zerotrie",
     "ffi/capi_cdylib",
     "ffi/capi_staticlib",
     "ffi/diplomat",

experimental/zerotrie/Cargo.toml

@@ -0,0 +1,67 @@
+# This file is part of ICU4X. For terms of use, please see the file
+# called LICENSE at the top level of the ICU4X source tree
+# (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+[package]
+name = "zerotrie"
+description = "A data structure that efficiently maps strings to integers"
+version = "0.1.0"
+authors = ["The ICU4X Project Developers"]
+edition = "2021"
+readme = "README.md"
+repository = "https://github.com/unicode-org/icu4x"
+license = "Unicode-DFS-2016"
+# Keep this in sync with other crates unless there are exceptions
+include = [
+    "src/**/*",
+    "examples/**/*",
+    "benches/**/*",
+    "tests/**/*",
+    "Cargo.toml",
+    "LICENSE",
+    "README.md"
+]
+
+[package.metadata.docs.rs]
+all-features = true
+
+[package.metadata.cargo-all-features]
+# Bench feature gets tested separately and is only relevant for CI
+denylist = ["bench"]
+
+[dependencies]
+zerovec = { path = "../../utils/zerovec", optional = true }
+litemap = { path = "../../utils/litemap", default-features = false, features = ["alloc"], optional = true }
+serde = { version = "1.0", optional = true }
+displaydoc = { version = "0.2.3", default-features = false }
+
+[dev-dependencies]
+postcard = { version = "1.0", default-features = false, features = ["alloc"] }
+serde = { version = "1.0", default-features = false }
+zerovec = { path = "../../utils/zerovec", features = ["serde", "hashmap"] }
+litemap = { path = "../../utils/litemap" }
+criterion = "0.4"
+icu_benchmark_macros = { path = "../../tools/benchmark/macros" }
+serde_json = "1.0"
+bincode = "1.0"
+rand = "0.8"
+rand_pcg = "0.3"
+
+[lib]
+bench = false  # This option is required for Benchmark CI
+path = "src/lib.rs"
+
+[features]
+default = []
+bench = []
+alloc = []
+litemap = ["dep:litemap", "alloc"]
+serde = ["dep:serde", "dep:litemap", "alloc", "litemap/serde", "zerovec?/serde"]
+
+[[bench]]
+name = "overview"
+harness = false
+
+[[test]]
+name = "builder_test"
+required-features = ["alloc", "litemap"]

experimental/zerotrie/LICENSE

@@ -0,0 +1,51 @@
+UNICODE, INC. LICENSE AGREEMENT - DATA FILES AND SOFTWARE
+
+See Terms of Use <https://www.unicode.org/copyright.html>
+for definitions of Unicode Inc.’s Data Files and Software.
+
+NOTICE TO USER: Carefully read the following legal agreement.
+BY DOWNLOADING, INSTALLING, COPYING OR OTHERWISE USING UNICODE INC.'S
+DATA FILES ("DATA FILES"), AND/OR SOFTWARE ("SOFTWARE"),
+YOU UNEQUIVOCALLY ACCEPT, AND AGREE TO BE BOUND BY, ALL OF THE
+TERMS AND CONDITIONS OF THIS AGREEMENT.
+IF YOU DO NOT AGREE, DO NOT DOWNLOAD, INSTALL, COPY, DISTRIBUTE OR USE
+THE DATA FILES OR SOFTWARE.
+
+COPYRIGHT AND PERMISSION NOTICE
+
+Copyright © 1991-2022 Unicode, Inc. All rights reserved.
+Distributed under the Terms of Use in https://www.unicode.org/copyright.html.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the Unicode data files and any associated documentation
+(the "Data Files") or Unicode software and any associated documentation
+(the "Software") to deal in the Data Files or Software
+without restriction, including without limitation the rights to use,
+copy, modify, merge, publish, distribute, and/or sell copies of
+the Data Files or Software, and to permit persons to whom the Data Files
+or Software are furnished to do so, provided that either
+(a) this copyright and permission notice appear with all copies
+of the Data Files or Software, or
+(b) this copyright and permission notice appear in associated
+Documentation.
+
+THE DATA FILES AND SOFTWARE ARE 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 OF THIRD PARTY RIGHTS.
+IN NO EVENT SHALL THE COPYRIGHT HOLDER OR HOLDERS INCLUDED IN THIS
+NOTICE BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL
+DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
+DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THE DATA FILES OR SOFTWARE.
+
+Except as contained in this notice, the name of a copyright holder
+shall not be used in advertising or otherwise to promote the sale,
+use or other dealings in these Data Files or Software without prior
+written authorization of the copyright holder.
+
+—
+
+Portions of ICU4X may have been adapted from ICU4C and/or ICU4J.
+ICU 1.8.1 to ICU 57.1 © 1995-2016 International Business Machines Corporation and others.