diff --git a/.github/workflows/cbindgen.yml b/.github/workflows/cbindgen.yml
index 4d4d54a97..bf2791329 100644
--- a/.github/workflows/cbindgen.yml
+++ b/.github/workflows/cbindgen.yml
@@ -41,11 +41,11 @@ jobs:
       uses: actions-rs/toolchain@v1
       with:
         profile: minimal
-        toolchain: 1.40.0
+        toolchain: 1.54.0
 
     - name: Build with minimum supported Rust version
       run: |
-        cargo +1.40.0 test nonexistent-test --verbose
+        cargo +1.54.0 test nonexistent-test --verbose
 
   build:
 
diff --git a/CHANGES b/CHANGES
index 646fdf050..0e0a7bba8 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,14 @@
+## 0.21.0
+
+      * Update MSRV to 1.54.0
+      * Update clap to 3.1.
+      * Update heck to 0.4.0
+      * unraw identifiers
+      * Honor documentation_length in Cython.
+      * Add documentation_style to with short and full options
+      * Map RawFd to Int
+      * Respect remove_underscores config when prefixing name to enum
+
 ## 0.20.0
 
      * Add Builder::with_using_namespaces. (#688)
diff --git a/Cargo.lock b/Cargo.lock
index caa9d1d26..7a1f1b6d6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,15 +2,6 @@
 # It is not intended for manual editing.
 version = 3
 
-[[package]]
-name = "ansi_term"
-version = "0.11.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ee49baf6cb617b853aa8d93bf420db2383fab46d314482ca2803b40d5fde979b"
-dependencies = [
- "winapi",
-]
-
 [[package]]
 name = "atty"
 version = "0.2.14"
@@ -36,7 +27,7 @@ checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
 
 [[package]]
 name = "cbindgen"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "clap",
  "heck",
@@ -60,17 +51,17 @@ checksum = "4785bdd1c96b2a846b2bd7cc02e86b6b3dbf14e7e53446c4f54c92a361040822"
 
 [[package]]
 name = "clap"
-version = "2.33.3"
+version = "3.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "37e58ac78573c40708d45522f0d80fa2f01cc4f9b4e2bf749807255454312002"
+checksum = "d8c93436c21e4698bacadf42917db28b23017027a4deccb35dbe47a7e7840123"
 dependencies = [
- "ansi_term",
  "atty",
  "bitflags",
+ "indexmap",
+ "os_str_bytes",
  "strsim",
+ "termcolor",
  "textwrap",
- "unicode-width",
- "vec_map",
 ]
 
 [[package]]
@@ -101,12 +92,9 @@ checksum = "d7afe4a420e3fe79967a00898cc1f4db7c8a49a9333a29f8a4bd76a253d5cd04"
 
 [[package]]
 name = "heck"
-version = "0.3.1"
+version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "20564e78d53d2bb135c343b3f47714a56af2061f1c928fdb541dc7b9fdd94205"
-dependencies = [
- "unicode-segmentation",
-]
+checksum = "2540771e65fc8cb83cd6e8a237f70c319bd5c29f78ed1084ba5d50eeac86f7f9"
 
 [[package]]
 name = "hermit-abi"
@@ -163,6 +151,21 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "memchr"
+version = "2.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "308cc39be01b73d0d18f82a0e7b2a3df85245f84af96fdddc5d202d27e47b86a"
+
+[[package]]
+name = "os_str_bytes"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e22443d1643a904602595ba1cd8f7d896afe56d26712531c5ff73a15b2fbf64"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "parking_lot"
 version = "0.10.2"
@@ -340,9 +343,9 @@ checksum = "fbee7696b84bbf3d89a1c2eccff0850e3047ed46bfcd2e92c29a2d074d57e252"
 
 [[package]]
 name = "strsim"
-version = "0.8.0"
+version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8ea5119cdb4c55b55d432abb513a0429384878c15dde60cc77b1c99de1a95a6a"
+checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
 
 [[package]]
 name = "syn"
@@ -370,14 +373,20 @@ dependencies = [
 ]
 
 [[package]]
-name = "textwrap"
-version = "0.11.0"
+name = "termcolor"
+version = "1.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d326610f408c7a4eb6f51c37c330e496b08506c9457c9d34287ecc38809fb060"
+checksum = "bab24d30b911b2376f3a13cc2cd443142f0c81dda04c118693e35b3835757755"
 dependencies = [
- "unicode-width",
+ "winapi-util",
 ]
 
+[[package]]
+name = "textwrap"
+version = "0.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b1141d4d61095b28419e22cb0bbf02755f5e54e0526f97f1e3d1d160e60885fb"
+
 [[package]]
 name = "toml"
 version = "0.5.6"
@@ -387,30 +396,12 @@ dependencies = [
  "serde",
 ]
 
-[[package]]
-name = "unicode-segmentation"
-version = "1.6.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e83e153d1053cbb5a118eeff7fd5be06ed99153f00dbcd8ae310c5fb2b22edc0"
-
-[[package]]
-name = "unicode-width"
-version = "0.1.8"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9337591893a19b88d8d87f2cec1e73fad5cdfd10e5a6f349f498ad6ea2ffb1e3"
-
 [[package]]
 name = "unicode-xid"
 version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
 
-[[package]]
-name = "vec_map"
-version = "0.8.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f1bddf1187be692e79c5ffeab891132dfb0f236ed36a43c7ed39f1165ee20191"
-
 [[package]]
 name = "wasi"
 version = "0.9.0+wasi-snapshot-preview1"
@@ -433,6 +424,15 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
 
+[[package]]
+name = "winapi-util"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "70ec6ce85bb158151cae5e5c87f95a8e97d2c0c4b001223f33a334e3ce5de178"
+dependencies = [
+ "winapi",
+]
+
 [[package]]
 name = "winapi-x86_64-pc-windows-gnu"
 version = "0.4.0"
diff --git a/Cargo.toml b/Cargo.toml
index 3030f963f..49fb036b5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "cbindgen"
-version = "0.20.0"
+version = "0.21.0"
 authors = [
   "Emilio Cobos Álvarez <emilio@crisal.io>",
   "Jeff Muizelaar <jmuizelaar@mozilla.com>",
@@ -21,7 +21,7 @@ exclude = [
 travis-ci = { repository = "eqrion/cbindgen" }
 
 [dependencies]
-clap = { version = "2", optional = true }
+clap = { version = "3.1", optional = true }
 indexmap = "1"
 log = "0.4"
 serde = { version = "1.0.103", default-features = false, features = ["derive"]}
@@ -30,7 +30,7 @@ tempfile = "3.0"
 toml = "0.5"
 proc-macro2 = "1"
 quote = "1"
-heck = "0.3"
+heck = "0.4"
 
 [dependencies.syn]
 version = "1.0.3"
diff --git a/README.md b/README.md
index b33cede83..837f7eca4 100644
--- a/README.md
+++ b/README.md
@@ -79,7 +79,6 @@ in production:
 * [milksnake](https://github.com/getsentry/milksnake)
 * [webrender](https://searchfox.org/mozilla-central/source/gfx/webrender_bindings) ([generated header](https://searchfox.org/mozilla-central/source/__GENERATED__/gfx/webrender_bindings/webrender_ffi_generated.h))
 * [stylo](https://searchfox.org/mozilla-central/source/layout/style) ([generated header](https://searchfox.org/mozilla-central/source/__GENERATED__/layout/style/ServoStyleConsts.h))
-* [etesync-rs](https://github.com/etesync/etesync-rs)
 
 If you're using `cbindgen` and would like to be added to this list, please open
 a pull request!
diff --git a/src/bindgen/rename.rs b/src/bindgen/rename.rs
index 0f6a93e0c..f559289dd 100644
--- a/src/bindgen/rename.rs
+++ b/src/bindgen/rename.rs
@@ -69,11 +69,11 @@ impl RenameRule {
 
         Cow::Owned(match self {
             RenameRule::None => return Cow::Borrowed(text),
-            RenameRule::GeckoCase => context.to_str().to_owned() + &text.to_camel_case(),
+            RenameRule::GeckoCase => context.to_str().to_owned() + &text.to_upper_camel_case(),
             RenameRule::LowerCase => text.to_lowercase(),
             RenameRule::UpperCase => text.to_uppercase(),
-            RenameRule::PascalCase => text.to_camel_case(),
-            RenameRule::CamelCase => text.to_mixed_case(),
+            RenameRule::PascalCase => text.to_pascal_case(),
+            RenameRule::CamelCase => text.to_upper_camel_case(),
             RenameRule::SnakeCase => text.to_snake_case(),
             RenameRule::ScreamingSnakeCase => text.to_shouty_snake_case(),
             RenameRule::QualifiedScreamingSnakeCase => {
diff --git a/src/main.rs b/src/main.rs
index 3e30ca584..35489c1c4 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -20,14 +20,14 @@ extern crate quote;
 extern crate syn;
 extern crate toml;
 
-use clap::{App, Arg, ArgMatches};
+use clap::{Arg, ArgMatches, Command};
 
 mod bindgen;
 mod logging;
 
 use crate::bindgen::{Bindings, Builder, Cargo, Config, Error, Profile, Style};
 
-fn apply_config_overrides<'a>(config: &mut Config, matches: &ArgMatches<'a>) {
+fn apply_config_overrides(config: &mut Config, matches: &ArgMatches) {
     // We allow specifying a language to override the config default. This is
     // used by compile-tests.
     if let Some(lang) = matches.value_of("lang") {
@@ -78,7 +78,7 @@ fn apply_config_overrides<'a>(config: &mut Config, matches: &ArgMatches<'a>) {
     }
 }
 
-fn load_bindings<'a>(input: &Path, matches: &ArgMatches<'a>) -> Result<Bindings, Error> {
+fn load_bindings(input: &Path, matches: &ArgMatches) -> Result<Bindings, Error> {
     // If a file is specified then we load it as a single source
     if !input.is_dir() {
         // Load any config specified or search in the input directory
@@ -130,62 +130,62 @@ fn load_bindings<'a>(input: &Path, matches: &ArgMatches<'a>) -> Result<Bindings,
 }
 
 fn main() {
-    let matches = App::new("cbindgen")
+    let matches = Command::new("cbindgen")
         .version(bindgen::VERSION)
         .about("Generate C bindings for a Rust library")
         .arg(
-            Arg::with_name("v")
-                .short("v")
-                .multiple(true)
+            Arg::new("v")
+                .short('v')
+                .multiple_occurrences(true)
                 .help("Enable verbose logging"),
         )
         .arg(
-            Arg::with_name("verify")
+            Arg::new("verify")
                 .long("verify")
                 .help("Generate bindings and compare it to the existing bindings file and error if they are different"),
         )
         .arg(
-            Arg::with_name("config")
-                .short("c")
+            Arg::new("config")
+                .short('c')
                 .long("config")
                 .value_name("PATH")
                 .help("Specify path to a `cbindgen.toml` config to use"),
         )
         .arg(
-            Arg::with_name("lang")
-                .short("l")
+            Arg::new("lang")
+                .short('l')
                 .long("lang")
                 .value_name("LANGUAGE")
                 .help("Specify the language to output bindings in")
                 .possible_values(&["c++", "C++", "c", "C", "cython", "Cython", "zig", "Zig"]),
         )
         .arg(
-            Arg::with_name("cpp-compat")
+            Arg::new("cpp-compat")
                 .long("cpp-compat")
                 .help("Whether to add C++ compatibility to generated C bindings")
         )
         .arg(
-            Arg::with_name("only-target-dependencies")
+            Arg::new("only-target-dependencies")
                 .long("only-target-dependencies")
                 .help("Only fetch dependencies needed by the target platform. \
                     The target platform defaults to the host platform; set TARGET to override.")
         )
         .arg(
-            Arg::with_name("style")
-                .short("s")
+            Arg::new("style")
+                .short('s')
                 .long("style")
                 .value_name("STYLE")
                 .help("Specify the declaration style to use for bindings")
                 .possible_values(&["Both", "both", "Tag", "tag", "Type", "type"]),
         )
         .arg(
-            Arg::with_name("d")
-                .short("d")
+            Arg::new("d")
+                .short('d')
                 .long("parse-dependencies")
                 .help("Whether to parse dependencies when generating bindings"),
         )
         .arg(
-            Arg::with_name("clean")
+            Arg::new("clean")
                 .long("clean")
                 .help(
                     "Whether to use a new temporary directory for expanding macros. \
@@ -193,7 +193,7 @@ fn main() {
                 .required(false)
         )
         .arg(
-            Arg::with_name("INPUT")
+            Arg::new("INPUT")
                 .help(
                     "A crate directory or source file to generate bindings for. \
                     In general this is the folder where the Cargo.toml file of \
@@ -202,7 +202,7 @@ fn main() {
                 .index(1),
         )
         .arg(
-            Arg::with_name("crate")
+            Arg::new("crate")
                 .long("crate")
                 .value_name("CRATE_NAME")
                 .help(
@@ -212,15 +212,15 @@ fn main() {
                 .required(false),
         )
         .arg(
-            Arg::with_name("out")
-                .short("o")
+            Arg::new("out")
+                .short('o')
                 .long("output")
                 .value_name("PATH")
                 .help("The file to output the bindings to")
                 .required(false),
         )
         .arg(
-            Arg::with_name("lockfile")
+            Arg::new("lockfile")
                 .long("lockfile")
                 .value_name("PATH")
                 .help(
@@ -231,7 +231,7 @@ fn main() {
                 .required(false),
         )
         .arg(
-            Arg::with_name("metadata")
+            Arg::new("metadata")
                 .long("metadata")
                 .value_name("PATH")
                 .help(
@@ -246,7 +246,7 @@ fn main() {
                 .required(false),
         )
         .arg(
-            Arg::with_name("profile")
+            Arg::new("profile")
                 .long("profile")
                 .value_name("PROFILE")
                 .help(
@@ -256,8 +256,8 @@ fn main() {
                 .possible_values(&["Debug", "debug", "Release", "release"]),
         )
         .arg(
-            Arg::with_name("quiet")
-                .short("q")
+            Arg::new("quiet")
+                .short('q')
                 .long("quiet")
                 .help("Report errors only (overrides verbosity options).")
                 .required(false),