Add 2018-specific changes.

Author: ehuss

src/SUMMARY.md

@@ -83,4 +83,5 @@
       - [Global allocators](rust-2018/platform-and-target-support/global-allocators.md)
       - [MSVC toolchain support](rust-2018/platform-and-target-support/msvc-toolchain-support.md)
       - [MUSL support for fully static binaries](rust-2018/platform-and-target-support/musl-support-for-fully-static-binaries.md)
-      - [`cdylib` crates for C interoperability](rust-2018/platform-and-target-support/cdylib-crates-for-c-interoperability.md)
+      - [`cdylib` crates for C interoperability](rust-2018/platform-and-target-support/cdylib-crates-for-c-interoperability.md)
+    - [2018-Specific Changes](rust-2018/edition-changes.md)

src/rust-2018/edition-changes.md

@@ -0,0 +1,47 @@
+# 2018-Specific Changes
+
+The following is a summary of changes that only apply to code compiled with
+the 2018 edition compared to the 2015 edition.
+
+## Rust
+- [Non-lexical lifetimes].
+- [At most once] `?` macro repetition operator.
+- [Path changes]:
+    - `use` declarations must begin with:
+        - `crate` – refers to the current crate.
+        - `self` – refers to the current module.
+        - `super` – refers to the parent module.
+        - An external crate name.
+        - `::` – must be followed by an external crate name. This is required
+          if an external crate has the same name as an in-scope item, to catch
+          possible ambiguities with future module changes.
+    - Paths in `pub(in path)` visibility modifiers must start with `crate`,
+      `self`, or `super`.
+- [Anonymous trait function parameters] are not allowed.
+    - [Trait function parameters] may use any irrefutable pattern when the
+      function has a body.
+- [`dyn`] is a [strict keyword], in 2015 it is a [weak keyword].
+- `async`, `await`, and `try` are [reserved keywords].
+- The following lints are now deny by default:
+    - [overflowing_literals]
+    - [tyvar_behind_raw_pointer]
+
+## Cargo
+- If there is a target definition in a `Cargo.toml` manifest, it no longer
+  automatically disables automatic discovery of other targets.
+- Target paths of the form `src/{target_name}.rs` are no longer inferred for
+  targets where the `path` field is not set.
+- `cargo install` for the current directory is no longer allowed, you must
+  specify `cargo install --path .` to install the current package.
+
+[Anonymous trait function parameters]: rust-2018/trait-system/no-anon-params.html
+[At most once]: rust-2018/macros/at-most-once.html
+[Non-lexical lifetimes]: rust-2018/ownership-and-lifetimes/non-lexical-lifetimes.html
+[Path changes]: rust-2018/module-system/path-clarity.html
+[Trait function parameters]: https://doc.rust-lang.org/stable/reference/items/traits.html#parameter-patterns
+[`dyn`]: rust-2018/trait-system/dyn-trait-for-trait-objects.html
+[overflowing_literals]: https://github.com/rust-lang/rfcs/blob/master/text/2438-deny-integer-literal-overflow-lint.md
+[reserved keywords]: https://doc.rust-lang.org/reference/keywords.html#reserved-keywords
+[strict keyword]: https://doc.rust-lang.org/reference/keywords.html#strict-keywords
+[tyvar_behind_raw_pointer]: https://github.com/rust-lang/rust/issues/46906
+[weak keyword]: https://doc.rust-lang.org/reference/keywords.html#weak-keywords