Add linting for trailing whitespaces, newline symbols, etc.

This PR adds configuration for `pre-commit` tool, which can run `rustfmt`
and a few other tools to ensure code style. Contrary to its name,
`pre-commit` doesn't have to be installed as a pre-commit hook.
Instead, it can be invoked manually instead of `cargo fmt`, or registered
as a pre-push hook.

I've enabled several useful checks/fixes: trailing whitespace,
trailing newlines, line encoding, validity of json/yaml/toml files,
lint that finds files broken by merge conflicts, and a few others.

I've also added settings for VSCode to fix trailing whitespaces and newlines
on file save.

# Motivation

Some contributors have their editors configured to trim trailing whitespaces
and newlines on save, while others don't. This results in spurious changes
because somebody's editor added or removed a newline at the end of file.

Hopefully this change will make them less prevalent, if at all.

Author: taminomara

.github/workflows/test.yml

@@ -25,15 +25,17 @@ jobs:
       uses: crate-ci/typos@master
 
   reformat:
-    name: Rustfmt
+    name: Code Style Check
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
       uses: actions/checkout@v4
     - name: Install Rust toolchain
       uses: dtolnay/rust-toolchain@stable
-    - name: Run Rustfmt
-      run: cargo fmt --all -- --check
+    - name: Install pre-commit
+      run: pip install pre-commit
+    - name: Run style check
+      run: pre-commit run --all
 
   test:
     runs-on: ubuntu-latest

.pre-commit-config.yaml

@@ -0,0 +1,30 @@
+repos:
+  - repo: local
+    hooks:
+      - id: fmt
+        name: fmt
+        description: run cargo fmt
+        entry: cargo fmt
+        language: system
+        types: [ rust ]
+        args: [ "--all" ]
+        pass_filenames: false
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v6.0.0
+    hooks:
+      - id: trailing-whitespace
+      - id: end-of-file-fixer
+      - id: fix-byte-order-marker
+      - id: mixed-line-ending
+        args: [ --fix=lf ]
+      - id: check-added-large-files
+      - id: check-yaml
+      - id: check-toml
+      - id: check-json
+        exclude: ^.vscode/
+      - id: check-merge-conflict
+      - id: check-shebang-scripts-are-executable
+        exclude_types: [ rust ]
+      - id: check-symlinks
+      - id: destroyed-symlinks
+      - id: check-vcs-permalinks

.vscode/settings.json

@@ -1 +1,7 @@
-{}
+{
+    "files.eol": "\n",
+    "files.insertFinalNewline": true,
+    "files.trimFinalNewlines": true,
+    "files.trimTrailingWhitespace": true,
+    "files.trimTrailingWhitespaceInRegexAndStrings": true
+}