Fun with clang-format
28 Jun 2025There are formatting options that are a matter of taste and there are formatting options that severely affect readability and maintenance. Consider this code:
Fooooooooooooooooooooo::Fooooooooooooooooooooo(
int arrrrrrrrrrrrrrrrrrrrrg1,
int arrrrrrrrrrrrrrrrrrrrrg2,
int arrrrrrrrrrrrrrrrrrrrrg3) :
Foo(arrrrrrrrrrrrrrrrrrrrrg1),
Bar(arrrrrrrrrrrrrrrrrrrrrg2) {
Baz(arrrrrrrrrrrrrrrrrrrrrg3);
}
void Fooooooooooooooooooooo::Baz(int arg) {
switch (arg) {
default: {
break;
}
case 21:
break;
}
}In the first example, it is hard to distinguish between the initializer list and the function body. In the second function, it is hard to spot the end of the switch statement.
But how does the formatting change if we run this through clang-format with
the built-in presets?
LLVM:
Fooooooooooooooooooooo::Fooooooooooooooooooooo(int arrrrrrrrrrrrrrrrrrrrrg1,
int arrrrrrrrrrrrrrrrrrrrrg2,
int arrrrrrrrrrrrrrrrrrrrrg3)
: Foo(arrrrrrrrrrrrrrrrrrrrrg1), Bar(arrrrrrrrrrrrrrrrrrrrrg2) {
Baz(arrrrrrrrrrrrrrrrrrrrrg3);
}
void Fooooooooooooooooooooo::Baz(int arg) {
switch (arg) {
default: {
break;
}
case 21:
break;
}
}GNU:
Fooooooooooooooooooooo::Fooooooooooooooooooooo (int arrrrrrrrrrrrrrrrrrrrrg1,
int arrrrrrrrrrrrrrrrrrrrrg2,
int arrrrrrrrrrrrrrrrrrrrrg3)
: Foo (arrrrrrrrrrrrrrrrrrrrrg1), Bar (arrrrrrrrrrrrrrrrrrrrrg2)
{
Baz (arrrrrrrrrrrrrrrrrrrrrg3);
}
void
Fooooooooooooooooooooo::Baz (int arg)
{
switch (arg)
{
default:
{
break;
}
case 21:
break;
}
}Google:
Fooooooooooooooooooooo::Fooooooooooooooooooooo(int arrrrrrrrrrrrrrrrrrrrrg1,
int arrrrrrrrrrrrrrrrrrrrrg2,
int arrrrrrrrrrrrrrrrrrrrrg3)
: Foo(arrrrrrrrrrrrrrrrrrrrrg1), Bar(arrrrrrrrrrrrrrrrrrrrrg2) {
Baz(arrrrrrrrrrrrrrrrrrrrrg3);
}
void Fooooooooooooooooooooo::Baz(int arg) {
switch (arg) {
default: {
break;
}
case 21:
break;
}
}Chromium:
Fooooooooooooooooooooo::Fooooooooooooooooooooo(int arrrrrrrrrrrrrrrrrrrrrg1,
int arrrrrrrrrrrrrrrrrrrrrg2,
int arrrrrrrrrrrrrrrrrrrrrg3)
: Foo(arrrrrrrrrrrrrrrrrrrrrg1), Bar(arrrrrrrrrrrrrrrrrrrrrg2) {
Baz(arrrrrrrrrrrrrrrrrrrrrg3);
}
void Fooooooooooooooooooooo::Baz(int arg) {
switch (arg) {
default: {
break;
}
case 21:
break;
}
}Microsoft:
Fooooooooooooooooooooo::Fooooooooooooooooooooo(int arrrrrrrrrrrrrrrrrrrrrg1, int arrrrrrrrrrrrrrrrrrrrrg2,
int arrrrrrrrrrrrrrrrrrrrrg3)
: Foo(arrrrrrrrrrrrrrrrrrrrrg1), Bar(arrrrrrrrrrrrrrrrrrrrrg2)
{
Baz(arrrrrrrrrrrrrrrrrrrrrg3);
}
void Fooooooooooooooooooooo::Baz(int arg)
{
switch (arg)
{
default: {
break;
}
case 21:
break;
}
}Mozilla:
Fooooooooooooooooooooo::Fooooooooooooooooooooo(int arrrrrrrrrrrrrrrrrrrrrg1,
int arrrrrrrrrrrrrrrrrrrrrg2,
int arrrrrrrrrrrrrrrrrrrrrg3)
: Foo(arrrrrrrrrrrrrrrrrrrrrg1)
, Bar(arrrrrrrrrrrrrrrrrrrrrg2)
{
Baz(arrrrrrrrrrrrrrrrrrrrrg3);
}
void
Fooooooooooooooooooooo::Baz(int arg)
{
switch (arg) {
default: {
break;
}
case 21:
break;
}
}WebKit:
Fooooooooooooooooooooo::Fooooooooooooooooooooo(
int arrrrrrrrrrrrrrrrrrrrrg1,
int arrrrrrrrrrrrrrrrrrrrrg2,
int arrrrrrrrrrrrrrrrrrrrrg3)
: Foo(arrrrrrrrrrrrrrrrrrrrrg1)
, Bar(arrrrrrrrrrrrrrrrrrrrrg2)
{
Baz(arrrrrrrrrrrrrrrrrrrrrg3);
}
void Fooooooooooooooooooooo::Baz(int arg)
{
switch (arg) {
default: {
break;
}
case 21:
break;
}
}Having the opening brace for functions on a separate line really helps finding the beginning of the function body of a constructor. This is done well in the presets for GNU, Microsoft, Mozilla, and WebKit.
Indenting the case statements of a switch statement is necessary when cases introduce their own scope. This is done well in the presets for GNU, Google, Chromium, and Mozilla.
Aligning function arguments on the opening parenthesis moves them out of the attention area. Especially in the case of the preset for Mozilla, the function header looks disconnected from the body of the function. Another problem is that this alignment requires changing the indentation of the arguments in case the function name is changed. Only the WebKit preset does a good job here, even though it does not produce perfectly readable formatting either: It is still hard to distinguish the function arguments from the initialier list.
I cannot recommend any of the builtin presets at the time of this writing.