Compile serde_derive separately from serde

When serde's derive feature is used, serde_derive must be
compiled before serde can be, as serde with that feature has a
serde_derive dependency.

As of serde 1.0.186, this issue can be avoided by adding a separate
serde_derive dependency due to the fact that serde 1.0.186 has a
never-applicable dependency on serde_derive, which ensures that
there is no incompatible version of serde_derive in a program [1].

Because MSRV being set to 1.56, it's not possible to use the dep:
syntax in features, so serde crate needs to be renamed.

This should improve compilation times of programs that use url
with its serde feature, provided it doesn't have other crates that
use serde with its derive feature.

[1]: serde-rs/serde#2588

url/Cargo.toml

@@ -17,22 +17,24 @@ edition = "2018"
 rust-version = "1.56"
 
 [dev-dependencies]
-serde = { version = "1.0", features = ["derive"] }
+serde_crate = { package = "serde", version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 bencher = "0.1"
 
 [dependencies]
 form_urlencoded = { version = "1.2.0", path = "../form_urlencoded" }
 idna = { version = "0.4.0", path = "../idna" }
 percent-encoding = { version = "2.3.0", path = "../percent_encoding" }
-serde = { version = "1.0", optional = true, features = ["derive"] }
+serde_crate = { package = "serde", version = "1.0.186", optional = true }
+serde_derive = { version = "1.0", optional = true }
 
 [features]
 default = []
 # Enable to use the #[debugger_visualizer] attribute. This feature requires Rust >= 1.71.
 debugger_visualizer = []
 # Expose internal offsets of the URL.
 expose_internals = []
+serde = ["serde_crate", "serde_derive"]
 
 [[test]]
 name = "url_wpt"

url/src/host.rs

@@ -12,11 +12,15 @@ use std::net::{Ipv4Addr, Ipv6Addr};
 
 use percent_encoding::{percent_decode, utf8_percent_encode, CONTROLS};
 #[cfg(feature = "serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 use crate::parser::{ParseError, ParseResult};
 
-#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
+#[cfg_attr(
+    feature = "serde",
+    derive(Deserialize, Serialize),
+    serde(crate = "serde"),
+)]
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub(crate) enum HostInternal {
     None,
@@ -37,7 +41,11 @@ impl From<Host<String>> for HostInternal {
 }
 
 /// The host name of an URL.
-#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
+#[cfg_attr(
+    feature = "serde",
+    derive(Deserialize, Serialize),
+    serde(crate = "serde"),
+)]
 #[derive(Clone, Debug, Eq, Ord, PartialOrd, Hash)]
 pub enum Host<S = String> {
     /// A DNS domain name, as '.' dot-separated labels.

url/src/lib.rs

@@ -143,7 +143,7 @@ url = { version = "2", features = ["debugger_visualizer"] }
 pub use form_urlencoded;
 
 #[cfg(feature = "serde")]
-extern crate serde;
+extern crate serde_crate as serde;
 
 use crate::host::HostInternal;
 use crate::parser::{to_u32, Context, Parser, SchemeType, PATH_SEGMENT, USERINFO};

url/tests/wpt.rs

@@ -8,6 +8,8 @@
 
 //! Data-driven tests imported from web-platform-tests
 
+extern crate serde_crate as serde;
+
 use std::collections::HashMap;
 use std::fmt::Write;
 use std::panic;
@@ -16,6 +18,7 @@ use serde_json::Value;
 use url::Url;
 
 #[derive(Debug, serde::Deserialize)]
+#[serde(crate = "serde")]
 struct UrlTest {
     input: String,
     base: Option<String>,
@@ -24,14 +27,15 @@ struct UrlTest {
 }
 
 #[derive(Debug, serde::Deserialize)]
-#[serde(untagged)]
+#[serde(crate = "serde", untagged)]
 #[allow(clippy::large_enum_variant)]
 enum UrlTestResult {
     Ok(UrlTestOk),
     Fail(UrlTestFail),
 }
 
 #[derive(Debug, serde::Deserialize)]
+#[serde(crate = "serde")]
 struct UrlTestOk {
     href: String,
     protocol: String,
@@ -46,18 +50,21 @@ struct UrlTestOk {
 }
 
 #[derive(Debug, serde::Deserialize)]
+#[serde(crate = "serde")]
 struct UrlTestFail {
     failure: bool,
 }
 
 #[derive(Debug, serde::Deserialize)]
+#[serde(crate = "serde")]
 struct SetterTest {
     href: String,
     new_value: String,
     expected: SetterTestExpected,
 }
 
 #[derive(Debug, serde::Deserialize)]
+#[serde(crate = "serde")]
 struct SetterTestExpected {
     href: Option<String>,
     protocol: Option<String>,