strings: builder.writeln() optimization

vlib/strings/builder.v

@@ -32,6 +32,7 @@ pub fn (mut b Builder) write_b(data byte) {
 	b.len++
 }
 
+[inline]
 pub fn (mut b Builder) write(s string) {
 	if s == '' {
 		return
@@ -77,6 +78,7 @@ pub fn (mut b Builder) go_back_to(pos int) {
 	b.len = pos
 }
 
+[inline]
 pub fn (mut b Builder) writeln(s string) {
 	// for c in s {
 	// b.buf << c

vlib/v/gen/cgen.v

@@ -3599,9 +3599,8 @@ fn (mut g Gen) write_expr_to_string(expr ast.Expr) string {
 	return g.out.cut_last(g.out.buf.len - pos)
 }
 
-fn (mut g Gen) start_tmp() {
+// fn (mut g Gen) start_tmp() {
-}
+// }
-
 // If user is accessing the return value eg. in assigment, pass the variable name.
 // If the user is not using the optional return value. We need to pass a temp var
 // to access its fields (`.ok`, `.error` etc)

vlib/v/gen/fn.v

@@ -270,7 +270,13 @@ fn (mut g Gen) call_expr(node ast.CallExpr) {
 		g.write('$styp $tmp_opt = ')
 	}
 	if node.is_method {
+		if node.name == 'writeln' && g.pref.show_cc &&
+			node.args.len > 0 && node.args[0].expr is ast.StringInterLiteral &&
+			g.table.get_type_symbol(node.receiver_type).name == 'strings.Builder' {
+			g.string_inter_literal_sb_optimized(node)
+		} else {
 			g.method_call(node)
+		}
 	} else {
 		g.fn_call(node)
 	}

vlib/v/gen/str.v

@@ -138,6 +138,54 @@ fn (mut g Gen) string_literal(node ast.StringLiteral) {
 	}
 }
 
+// optimize string interpolation in string builders:
+// `sb.writeln('a=$a')` =>
+// `sb.writeln('a='); sb.writeln(a.str())`
+fn (mut g Gen) string_inter_literal_sb_optimized(call_expr ast.CallExpr) {
+	node := call_expr.args[0].expr as ast.StringInterLiteral
+	// sb_name := g.cur_call_expr.left
+	// g.go_before_stmt(0)
+	g.writeln('// sb inter opt')
+	write := 'writeln'
+	/*
+	if node.vals.len != node.exprs.len {
+		println('NOPE')
+		println(node.vals)
+		println('==========')
+		println(node.exprs)
+	}
+	*/
+	for i, val in node.vals {
+		escaped_val := val.replace_each(['"', '\\"', '\r\n', '\\n', '\n', '\\n', '%', '%%'])
+		// if val == '' {
+		// break
+		// continue
+		// }
+		g.write('strings__Builder_${write}(&')
+		g.expr(call_expr.left)
+		g.write(', tos_lit("')
+		g.write(escaped_val)
+		g.writeln('"));')
+		//
+		if i >= node.exprs.len {
+			break
+		}
+		// if node.expr_types.len <= i || node.exprs.len <= i {
+		// continue
+		// }
+		g.write('strings__Builder_${write}(&')
+		g.expr(call_expr.left)
+		g.write(', ')
+		g.write(g.typ(node.expr_types[i]))
+		g.write('_str(')
+		g.expr(node.exprs[i])
+		g.writeln('));')
+	}
+	g.writeln('')
+	// println(node.vals)
+	return
+}
+
 fn (mut g Gen) string_inter_literal(node ast.StringInterLiteral) {
 	mut cur_line := ''
 	mut tmp := ''