Format code and add lint job in CI (#103)

* Separate lint job

* Fix formatting

* Derive Default for ErrorMessage enum

* Revert "Derive Default for ErrorMessage enum"

This reverts commit 9f43ceb.

* Ignore clippy::derivable_impls for ErrorMessage

.github/workflows/build.yml

@@ -11,6 +11,49 @@ env:
   MSRV: 1.58.1
 
 jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+        with:
+          # Make sure the actual branch is checked out when running on pull requests
+          ref: ${{ github.head_ref }}
+          fetch-depth: 1
+
+      - name: Install toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+          profile: minimal
+          components: rustfmt, clippy
+
+      - name: Cache cargo files
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cargo/bin
+            ~/.cargo/.crates.toml
+            ~/.cargo/.crates2.json
+            ~/.cargo/registry/index
+            ~/.cargo/registry/cache
+            ~/.cargo/git/db
+            ./target
+            ./test-target
+          key: ${{ runner.os }}-cargo-files-stable-${{ hashFiles('**/Cargo.lock', '**/Cargo.toml') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-files-stable
+
+      - name: Build
+        run: cargo build --all-features
+
+      - name: Check format
+        run: cargo fmt --check
+
+      - name: Check lint
+        run: cargo clippy -- -D warnings
+
   tests:
     runs-on: ${{ matrix.os }}
     strategy:
@@ -72,10 +115,6 @@ jobs:
       - name: Test (default)
         run: cargo test --verbose
 
-      - name: Test (all features)
-        if: matrix.os != 'windows-latest'
-        run: cargo test --verbose --all-features
-
       - name: Test (termion)
         if: matrix.os != 'windows-latest'
         run: cargo test --verbose --no-default-features --features=termion
@@ -86,6 +125,10 @@ jobs:
       - name: Test (console)
         run: cargo test --verbose --no-default-features --features=console
 
+      - name: Test (all features)
+        if: matrix.os != 'windows-latest'
+        run: cargo test --verbose --all-features
+
       - name: Check format
         if: ${{ false }}
         run: cargo fmt --check

src/terminal/termion.rs

@@ -1,5 +1,5 @@
 use core::fmt;
-use std::io::{stdin, stderr, Result, Stdin, Stderr, Write};
+use std::io::{stderr, stdin, Result, Stderr, Stdin, Write};
 
 use termion::{
     color::{self, Color},

src/validator.rs

@@ -28,6 +28,9 @@ pub enum ErrorMessage {
     Custom(String),
 }
 
+// Deriving an enum default was stabilized on v1.62 which would require us
+// to bump the MSRV to 1.62.0.
+#[allow(clippy::derivable_impls)]
 impl Default for ErrorMessage {
     fn default() -> Self {
         ErrorMessage::Default