add pre-commit hook (#6041)

* add pre-commit hook

Co-authored-by: Gianguido Sora <gsora@users.noreply.github.com>

* add go tools installation notes

* Update CONTRIBUTING.md

* run both go mod and golangci-lint

* silence which

* add go.mod go.sum after go mod tidy

* update README

* look up golangci-lint specifically in GOPATH/bin

* don't run golangci-lint

* exclude proto files

Co-authored-by: Gianguido Sora <gsora@users.noreply.github.com>
Co-authored-by: Alexander Bezobchuk <alexanderbez@users.noreply.github.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

contrib/githooks/README.md

@@ -0,0 +1,21 @@
+# Git hooks
+
+Installation:
+
+```
+$ git config core.hooksPath contrib/githooks
+```
+
+## pre-commit
+
+The hook automatically runs `gofmt`, `goimports`, and `misspell`
+to correctly format the `.go` files included in the commit, provided
+that all the aforementioned commands are installed and available
+in the user's search `$PATH` environment variable:
+
+```
+$ go get golang.org/x/tools/cmd/goimports
+$ go get github.com/golangci/misspell/cmd/misspell@master
+```
+
+It also runs `go mod tidy` and `golangci-lint` if available.

contrib/githooks/pre-commit

@@ -0,0 +1,41 @@
+#!/bin/bash
+
+set -e
+
+CMDS='git go gofmt goimports misspell'
+STAGED_GO_FILES=$(git diff --cached --name-only -- '*.go')
+
+f_echo_stderr() {
+  echo $@ >&2
+}
+
+f_exit_success() {
+  [ x"$@" != "x" ] && f_echo_stderr $@ || exit 0
+}
+trap f_exit_success EXIT
+
+f_check_cmds() {
+  for cmd in ${CMDS}; do
+    which ${cmd} &>/dev/null || f_exit_success "couldn't find ${cmd}, skipping"
+  done
+}
+
+f_check_cmds
+
+if [[ $STAGED_GO_FILES != "" ]]; then
+  f_echo_stderr "[pre-commit] fmt'ing staged files..."
+  for file in $STAGED_GO_FILES; do
+    if [[ $file =~ vendor/ ]] || [[ $file =~ client/lcd/statik/ ]] || [[ $file =~ tests/mocks/ ]] || [[ $file =~ \.pb\.go ]]; then
+      continue
+    fi
+
+    gofmt -w -s $file
+    misspell -w $file
+    goimports -w -local github.com/cosmos/cosmos-sdk $file
+    git add $file
+
+  done
+fi
+
+# Run go mod tidy
+go mod tidy && git add go.mod go.sum