improve flag doc with go 1.10+ (#56)

cmd/grpcurl/indent_test.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"bytes"
+	"flag"
+	"testing"
+)
+
+func TestFlagDocIndent(t *testing.T) {
+	// Tests the prettify() and indent() function. The indent() function
+	// differs by Go version, due to differences in "flags" package across
+	// versions. Run with multiple versions of Go to ensure that doc output
+	// is properly indented, regardless of Go version.
+
+	var fs flag.FlagSet
+	var buf bytes.Buffer
+	fs.SetOutput(&buf)
+
+	fs.String("foo", "", prettify(`
+		This is a flag doc string.
+		It has multiple lines.
+		More than two, actually.`))
+	fs.Int("bar", 100, prettify(`This is a simple flag doc string.`))
+	fs.Bool("baz", false, prettify(`
+		This is another long doc string.
+		It also has multiple lines. But not as long as the first one.`))
+
+	fs.PrintDefaults()
+
+	expected :=
+		`  -bar int
+    	This is a simple flag doc string. (default 100)
+  -baz
+    	This is another long doc string.
+    	It also has multiple lines. But not as long as the first one.
+  -foo string
+    	This is a flag doc string.
+    	It has multiple lines.
+    	More than two, actually.
+`
+
+	actual := buf.String()
+	if actual != expected {
+		t.Errorf("Flag output had wrong indentation.\nExpecting:\n%s\nGot:\n%s", expected, actual)
+	}
+}