feat: preserve indentation of multiline go string literals (#765)

parser/v2/formattestdata/multiline_string_literal_indentation_preserved.txt

@@ -0,0 +1,40 @@
+-- in --
+package main
+
+templ x() {
+	@something(`Hi
+some cool text
+
+foo 
+
+bar
+
+		`)
+	@something(`
+		something
+				`,
+	`
+				something
+				`,
+		)
+}
+-- out --
+package main
+
+templ x() {
+	@something(`Hi
+some cool text
+
+foo 
+
+bar
+
+		`)
+	@something(`
+		something
+				`,
+		`
+				something
+				`,
+	)
+}

parser/v2/types.go

@@ -194,20 +194,6 @@ func (exp TemplateFileGoExpression) Write(w io.Writer, indent int) error {
 	return err
 }
 
-func writeLinesIndented(w io.Writer, level int, s string) (err error) {
-	indent := strings.Repeat("\t", level)
-	lines := strings.Split(s, "\n")
-	indented := strings.Join(lines, "\n"+indent)
-	if _, err = io.WriteString(w, indent); err != nil {
-		return err
-	}
-	_, err = io.WriteString(w, indented)
-	if err != nil {
-		return
-	}
-	return
-}
-
 func writeIndent(w io.Writer, level int, s ...string) (err error) {
 	indent := strings.Repeat("\t", level)
 	if _, err = io.WriteString(w, indent); err != nil {
@@ -963,8 +949,32 @@ func (tee TemplElementExpression) Write(w io.Writer, indent int) error {
 	if err != nil {
 		source = []byte(tee.Expression.Value)
 	}
-	if err := writeLinesIndented(w, indent, "@"+string(source)); err != nil {
-		return err
+	// Indent all lines and re-format, we can then use this to only re-indent lines that gofmt would modify.
+	reformattedSource, err := format.Source(bytes.ReplaceAll(source, []byte("\n"), []byte("\n\t")))
+	if err != nil {
+		reformattedSource = source
+	}
+	sourceLines := bytes.Split(source, []byte("\n"))
+	reformattedSourceLines := bytes.Split(reformattedSource, []byte("\n"))
+	for i := range sourceLines {
+		if i == 0 {
+			if err := writeIndent(w, indent, "@"+string(sourceLines[i])); err != nil {
+				return err
+			}
+			continue
+		}
+		if _, err := io.WriteString(w, "\n"); err != nil {
+			return err
+		}
+		if string(sourceLines[i]) != string(reformattedSourceLines[i]) {
+			if _, err := io.WriteString(w, string(sourceLines[i])); err != nil {
+				return err
+			}
+			continue
+		}
+		if err := writeIndent(w, indent, string(sourceLines[i])); err != nil {
+			return err
+		}
 	}
 	if len(tee.Children) == 0 {
 		return nil