add exhaustive linter (#1166)

* wip

more

add new files

run command fixes

more

* go.mod

* order

* same package

* review comment

* enable linter in .golangci.yml

* add testcase for default-signifies-exhaustive: true

* adjust runGoErrchk instead

* disable the linter

* cleanup

* more cleanup

* cleanup

test/linters_test.go

@@ -17,9 +17,13 @@ import (
 
 func runGoErrchk(c *exec.Cmd, files []string, t *testing.T) {
 	output, err := c.CombinedOutput()
-	assert.Error(t, err)
-	_, ok := err.(*exec.ExitError)
-	assert.True(t, ok, err)
+	// The returned error will be nil if the test file does not have any issues
+	// and thus the linter exits with exit code 0. So perform the additional
+	// assertions only if the error is non-nil.
+	if err != nil {
+		_, ok := err.(*exec.ExitError)
+		assert.True(t, ok, err)
+	}
 
 	// TODO: uncomment after deprecating go1.11
 	// assert.Equal(t, exitcodes.IssuesFound, exitErr.ExitCode())