add indentnonempty function

docs/strings.md

@@ -256,6 +256,18 @@ indent 4 $lots_of_text
 
 The above will indent every line of text by 4 space characters.
 
+## indentnonempty
+
+The `indentnonempty` behaves the same as `indent`, but only indents non-empty
+lines (i.e., lines containing non-space characters). Empty lines are kept as-is.
+
+```
+indentnonempty 4 $lots_of_text
+```
+
+This is useful when indenting generated code as it avoids adding spaces to empty
+lines.
+
 ## nindent
 
 The `nindent` function is the same as the indent function, but prepends a new

functions.go

@@ -149,21 +149,22 @@ var genericMap = map[string]interface{}{
 	"wrap":      func(l int, s string) string { return util.Wrap(s, l) },
 	"wrapWith":  func(l int, sep, str string) string { return util.WrapCustom(str, l, sep, true) },
 	// Switch order so that "foobar" | contains "foo"
-	"contains":   func(substr string, str string) bool { return strings.Contains(str, substr) },
-	"hasPrefix":  func(substr string, str string) bool { return strings.HasPrefix(str, substr) },
-	"hasSuffix":  func(substr string, str string) bool { return strings.HasSuffix(str, substr) },
-	"quote":      quote,
-	"squote":     squote,
-	"cat":        cat,
-	"indent":     indent,
-	"nindent":    nindent,
-	"replace":    replace,
-	"plural":     plural,
-	"sha1sum":    sha1sum,
-	"sha256sum":  sha256sum,
-	"sha512sum":  sha512sum,
-	"adler32sum": adler32sum,
-	"toString":   strval,
+	"contains":       func(substr string, str string) bool { return strings.Contains(str, substr) },
+	"hasPrefix":      func(substr string, str string) bool { return strings.HasPrefix(str, substr) },
+	"hasSuffix":      func(substr string, str string) bool { return strings.HasSuffix(str, substr) },
+	"quote":          quote,
+	"squote":         squote,
+	"cat":            cat,
+	"indent":         indent,
+	"indentnonempty": indentnonempty,
+	"nindent":        nindent,
+	"replace":        replace,
+	"plural":         plural,
+	"sha1sum":        sha1sum,
+	"sha256sum":      sha256sum,
+	"sha512sum":      sha512sum,
+	"adler32sum":     adler32sum,
+	"toString":       strval,
 
 	// Wrap Atoi to stop errors.
 	"atoi":      func(a string) int { i, _ := strconv.Atoi(a); return i },

strings.go

@@ -111,6 +111,18 @@ func indent(spaces int, v string) string {
 	return pad + strings.Replace(v, "\n", "\n"+pad, -1)
 }
 
+func indentnonempty(spaces int, v string) string {
+	pad := strings.Repeat(" ", spaces)
+	lines := strings.Split(v, "\n")
+	for i, line := range lines {
+		if strings.TrimSpace(line) == "" {
+			continue
+		}
+		lines[i] = pad + line
+	}
+	return strings.Join(lines, "\n")
+}
+
 func nindent(spaces int, v string) string {
 	return "\n" + indent(spaces, v)
 }

strings_test.go

@@ -252,6 +252,21 @@ func TestIndent(t *testing.T) {
 	}
 }
 
+func TestIndentNonEmpty(t *testing.T) {
+	tpl := `{{indentnonempty 4 "a\nb\nc"}}`
+	if err := runt(tpl, "    a\n    b\n    c"); err != nil {
+		t.Error(err)
+	}
+	tpl = `{{indentnonempty 4 "a\n  \nb\nc"}}`
+	if err := runt(tpl, "    a\n  \n    b\n    c"); err != nil {
+		t.Error(err)
+	}
+	tpl = `{{indentnonempty 4 "a\n  \nb\nc\n"}}`
+	if err := runt(tpl, "    a\n  \n    b\n    c\n"); err != nil {
+		t.Error(err)
+	}
+}
+
 func TestNindent(t *testing.T) {
 	tpl := `{{nindent 4 "a\nb\nc"}}`
 	if err := runt(tpl, "\n    a\n    b\n    c"); err != nil {