Delete support for compilers without crate::-based module system

.github/workflows/ci.yml

@@ -83,12 +83,12 @@ jobs:
       - run: cd serde && cargo build
 
   more:
-    name: Rust 1.28.0
+    name: Rust 1.30.0
     runs-on: ubuntu-latest
     timeout-minutes: 45
     steps:
       - uses: actions/checkout@v3
-      - uses: dtolnay/rust-toolchain@1.28.0
+      - uses: dtolnay/rust-toolchain@1.30.0
         # Work around failing to parse manifest because editions are unstable.
       - run: sed -i /test_suite/d Cargo.toml
       - run: cd serde && cargo build --no-default-features

README.md

@@ -1,12 +1,12 @@
-# Serde   [![Build Status]][actions] [![Latest Version]][crates.io] [![serde: rustc 1.28+]][Rust 1.28] [![serde_derive: rustc 1.56+]][Rust 1.56]
+# Serde   [![Build Status]][actions] [![Latest Version]][crates.io] [![serde: rustc 1.30+]][Rust 1.30] [![serde_derive: rustc 1.56+]][Rust 1.56]
 
 [Build Status]: https://img.shields.io/github/actions/workflow/status/serde-rs/serde/ci.yml?branch=master
 [actions]: https://github.com/serde-rs/serde/actions?query=branch%3Amaster
 [Latest Version]: https://img.shields.io/crates/v/serde.svg
 [crates.io]: https://crates.io/crates/serde
-[serde: rustc 1.28+]: https://img.shields.io/badge/serde-rustc_1.28+-lightgray.svg
+[serde: rustc 1.30+]: https://img.shields.io/badge/serde-rustc_1.30+-lightgray.svg
 [serde_derive: rustc 1.56+]: https://img.shields.io/badge/serde_derive-rustc_1.56+-lightgray.svg
-[Rust 1.28]: https://blog.rust-lang.org/2018/08/02/Rust-1.28.html
+[Rust 1.30]: https://blog.rust-lang.org/2018/10/25/Rust-1.30.0.html
 [Rust 1.56]: https://blog.rust-lang.org/2021/10/21/Rust-1.56.0.html
 
 **Serde is a framework for *ser*ializing and *de*serializing Rust data structures efficiently and generically.**

serde/Cargo.toml

@@ -11,7 +11,7 @@ keywords = ["serde", "serialization", "no_std"]
 license = "MIT OR Apache-2.0"
 readme = "crates-io.md"
 repository = "https://github.com/serde-rs/serde"
-rust-version = "1.28"
+rust-version = "1.30"
 
 [dependencies]
 serde_derive = { version = "=1.0.179", optional = true, path = "../serde_derive" }