Pull request: scripts: improve go-lint

Merge in DNS/adguard-home from imp-lint-script to master

Squashed commit of the following:

commit 89a6e8343f9f0c7ea257899b5daac014bfb6b6df
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Dec 10 13:36:38 2020 +0300

    script: make go-lint more in line with HACKING.md

commit dc4e1519d25877a074f667fec696578c80d7baf3
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Dec 10 13:35:03 2020 +0300

    scripts: improve go-lint

HACKING.md

@@ -152,6 +152,8 @@ The rules are mostly sorted in the alphabetical order.
 
  *  Put spaces within `$( cmd )`, `$(( expr ))`, and `{ cmd; }`.
 
+ *  `snake_case`, not `camelCase`.
+
  *  Use `set -e -f -u` and also `set -x` in verbose mode.
 
  *  Use the `"$var"` form instead of the `$var` form, unless word splitting is

scripts/go-lint.sh

@@ -13,24 +13,44 @@ test "${EXITONERROR:=1}" = '0' && set +e || set -e
 # variables.
 set -f -u
 
-# blocklistimports is a simple check against unwanted packages.
+not_found_msg='
+looks like a binary not found error.
+make sure you have installed the linter binaries using:
+
+	$ make go-install-tools
+'
+
+not_found() {
+	if [ "$?" = '127' ]
+	then
+		# Code 127 is the exit status a shell uses when
+		# a command or a file is not found, according to the
+		# Bash Hackers wiki.
+		#
+		# See https://wiki.bash-hackers.org/dict/terms/exit_status.
+		echo "$not_found_msg" 1>&2
+	fi
+}
+trap not_found EXIT
+
+# blocklist_imports is a simple check against unwanted packages.
 # Currently it only looks for package log which is replaced by our own
 # package github.com/AdguardTeam/golibs/log.
-blocklistimports () {
+blocklist_imports() {
 	git grep -F -e '"log"' -- '*.go' || exit 0;
 }
 
 # underscores is a simple check against Go filenames with underscores.
-underscores () {
+underscores() {
 	git ls-files '*_*.go' | { grep -F -e '_darwin.go' \
 		-e '_freebsd.go' -e '_linux.go' -e '_others.go' \
 		-e '_test.go' -e '_unix.go' -e '_windows.go' \
 		-v || exit 0; }
 }
 
-# exitonoutput exits with a nonzero exit code if there is anything in
+# exit_on_output exits with a nonzero exit code if there is anything in
 # the command's combined output.
-exitonoutput() {
+exit_on_output() {
 	test "$VERBOSE" -lt '2' && set +x
 
 	cmd="$1"
@@ -57,11 +77,11 @@ exitonoutput() {
 	return "$exitcode"
 }
 
-exitonoutput blocklistimports
+exit_on_output blocklist_imports
 
-exitonoutput underscores
+exit_on_output underscores
 
-exitonoutput gofumpt --extra -l -s .
+exit_on_output gofumpt --extra -l -s .
 
 golint --set_exit_status ./...
 
@@ -87,7 +107,7 @@ nilness ./...
 # TODO(a.garipov): Enable errcheck fully after handling all errors,
 # including the deferred ones, properly.  Also, perhaps, enable --blank.
 # errcheck ./...
-exitonoutput sh -c '
+exit_on_output sh -c '
 	errcheck --asserts ./... |\
 		{ grep -e "defer" -e "_test\.go:" -v || exit 0; }
 '