Cannot set granular width configuration settings to 100% if max_width = 100

[tcharding]

Thanks for your work on rustfmt!

The granular width configuration settings are documented to be percentages of max_width (e.g. chain_width). However when max_width is set to 100 setting their values to 100 causes a warning

`fn_call_width` cannot have a value that exceeds `max_width`. `fn_call_width` will be set to the same value as `max_width`

The error message is both surprising and incorrect since fn_call_width = 100 is not a value that exceeds max_width.

This does not happen if max_width is 99 or 101.

The exact config options that trigger this bug are:

max_width = 100
use_small_heuristics = "Off"
fn_call_width = 100

$ rustfmt --version
rustfmt 1.4.38-stable (fe5b13d 2022-05-18)

---

Edit by @ytmimi (add a minimal reproducible code snippet):

macro_rules! foo {
    () => {};
}

[ytmimi]

Thanks for the report!

Just as a heads up, when filing an issue please try to include a minimum code example that can be used to reproduce the issue along with any configuration options needed to produce the issue. It was a little tricky to track down since I tried running rustfmt on a few files and I couldn't reproduce the error until I ran rustfmt against src/utils.rs. Doing so the error is emitted 4 times.

Running rustfmt with debug logging enabled (RUSTFMT_LOG=rustfmt=DEBUG rustfmt --config-path=issue_5404.toml --emit stdout src/utils.rs) reveals that this error is always emitted after calling replace_names:

[2022-06-28T17:05:55Z DEBUG rustfmt_nightly::macros] replace_names `zsp.source_callsite()` {"$sp": "zsp"}
`fn_call_width` cannot have a value that exceeds `max_width`. `fn_call_width` will be set to the same value as `max_width`

[2022-06-28T17:05:55Z DEBUG rustfmt_nightly::macros] replace_names `!zself.config.file_lines().is_all()
                && !zself
                    .config
                    .file_lines()
                    .intersects(&zself.parse_sess.lookup_line_range(zspan))` {"$span": "zspan", "$self": "zself"}
`fn_call_width` cannot have a value that exceeds `max_width`. `fn_call_width` will be set to the same value as `max_width`

[2022-06-28T17:05:55Z DEBUG rustfmt_nightly::macros] replace_names `if out_of_file_lines_range!(zself, zspan) {
                return None;
            }` {"$self": "zself", "$span": "zspan"}
`fn_call_width` cannot have a value that exceeds `max_width`. `fn_call_width` will be set to the same value as `max_width`

[2022-06-28T17:05:55Z DEBUG rustfmt_nightly::macros] replace_names `if out_of_file_lines_range!(zself, zspan) {
                zself.push_rewrite(zspan, None);
                return;
            }` {"$span": "zspan", "$self": "zself"}
`fn_call_width` cannot have a value that exceeds `max_width`. `fn_call_width` will be set to the same value as `max_width`

replace_names only gets called in MacroBranch::rewrite

rustfmt/src/macros.rs

Lines 483 to 486 in c4416f2

	// Replaces `$foo` with `zfoo`. We must check for name overlap to ensure we
	// aren't causing problems.
	// This should also work for escaped `$` variables, where we leave earlier `$`s.
	fn replace_names(input: &str) -> Option<(String, HashMap<String, String>)> {

And on line 1230 we adjust the max_width, which is where the issue is occurring.

rustfmt/src/macros.rs

Lines 1216 to 1230 in c4416f2

	let (body_str, substs) = replace_names(old_body)?;
	let has_block_body = old_body.starts_with('{');
	let mut config = context.config.clone();
	config.set().hide_parse_errors(true);
	result += " {";
	let body_indent = if has_block_body {
	shape.indent
	} else {
	shape.indent.block_indent(&config)
	};
	let new_width = config.max_width() - body_indent.width();
	config.set().max_width(new_width);

Config::set returns a ConfigSetter, and trying to set any of the width settings results in calling Config::set_heuristics.

rustfmt/src/config/config_type.rs

Lines 89 to 103 in c4416f2

	impl<'a> ConfigSetter<'a> {
	$(
	#[allow(unreachable_pub)]
	pub fn $i(&mut self, value: $ty) {
	(self.0).$i.2 = value;
	match stringify!($i) {
	"max_width"
	| "use_small_heuristics"
	| "fn_call_width"
	| "single_line_if_else_max_width"
	| "attr_fn_like_width"
	| "struct_lit_width"
	| "struct_variant_width"
	| "array_width"
	| "chain_width" => self.0.set_heuristics(),

Config::set_heuristics calls Config::set_width_heuristics.

rustfmt/src/config/config_type.rs

Lines 373 to 381 in c4416f2

	fn set_heuristics(&mut self) {
	let max_width = self.max_width.2;
	match self.use_small_heuristics.2 {
	Heuristics::Default =>
	self.set_width_heuristics(WidthHeuristics::scaled(max_width)),
	Heuristics::Max => self.set_width_heuristics(WidthHeuristics::set(max_width)),
	Heuristics::Off => self.set_width_heuristics(WidthHeuristics::null()),
	};
	}

Config::set_width_heuristics pretty much goes through all the width settings one by one and calls the get_width_value closure on each, leading to the error that you're seeing:

rustfmt/src/config/config_type.rs

Lines 294 to 314 in c4416f2

	fn set_width_heuristics(&mut self, heuristics: WidthHeuristics) {
	let max_width = self.max_width.2;
	let get_width_value = |
	was_set: bool,
	override_value: usize,
	heuristic_value: usize,
	config_key: &str,
	| -> usize {
	if !was_set {
	return heuristic_value;
	}
	if override_value > max_width {
	eprintln!(
	"`{0}` cannot have a value that exceeds `max_width`. \
	`{0}` will be set to the same value as `max_width`",
	config_key,
	);
	return max_width;
	}
	override_value
	};

[calebcartwright]

fwiw I know this has been reported before, but can't find the prior issues atm

[tcharding]

Wow @ytmimi, thorough research/response, thank you. I'll add the minimal repro next time.

[iago-lito]

Hi! I can also reproduce with the following:

.rustfmt.toml

max_width = 100 # Not strictly necessary to reproduce.
single_line_if_else_max_width = 100 # Any value above 92 produces the incorrect warning.

src/main.rs

macro_rules! anything { // Necessary to reproduce.
    () => {};
}

fn main() {
    let v = if a == b { String::new() } else { format!("anything") }; // Formatting does happen.
}

The following incorrect warning is then displayed:

$ cargo fmt
`single_line_if_else_max_width` cannot have a value that exceeds `max_width`. `single_line_if_else_max_width` will be set to the same value as `max_width`

Although the project seems correctly formatted. Was this minimal reproductible example the only blocking point?

[ferdonline]

Sorry If I'm late to the game, but I'm finding some inconsistency in rustfmt 1.6.0-nightly. It seems that while the value is checked as a percentage, it might be taken as the absolute value. Of course at line_width=100 we don't notice the difference, but I'm getting a reformat under these conditions:

max_width = 120
struct_lit_width = 80

(So max struct literal would be 96)
And the code

impl From<&Command> for CommandView {
    fn from(cmd: &Command) -> Self {
        Self { request_id: cmd.request_id, app_id: cmd.app_id, action: cmd.action.clone() }
    }
}

(line length: 92)

[ytmimi]

@ferdonline Your issue seems unrelated to the original since it's not triggering any warning messages from rustfmt. I'm pretty sure we only set granular width settings as a percentage of max_width when setting use_small_heuristics. Can you please open a new issue, and in addition to including the code snippet can you also include a snippet of how rustfmt is modifying the code, thanks!

[ferdonline]

we only set granular width settings as a percentage of max_width when setting use_small_heuristics

In that case then it's only a warning problem, as it's raised when

max_width = 120
struct_lit_width = 100

[ytmimi]

@ferdonline Please open a new issue so we can discuss it separately. I'm unable to reproduce any warning messages when using rustfmt 1.6.0-nightly (1c05d50c 2023-10-21).

I'm running:

rustfmt +nightly-2023-10-22 --config=max_width=120,struct_lit_width=100

[bergkvist]

I just experienced the same problem and put a few print statements into the rustfmt source code, which revealed the following behaviour:

// max_width = 100
// fn_call_width = 100

macro_rules! foo {
    () => {
        // max_width = 92
        // fn_call_width = 100

        // WARNING: `fn_call_width` cannot have a value that exceeds `max_width`. `fn_call_width` will be set to the same value as `max_width`
        // Which results in:
        // fn_call_width = 92
    };
}

Notice that rustfmt decreases max_width as it enters deeper scopes/nesting, but fn_call_width remains the same. I guess this saturation is actually desirable behaviour, but getting the context-less warning message causes more confusion than anything.

Interestingly, if you add an extra pair of brackets, max_width in the nested scope will be 96 instead of 92:

// max_width = 100
// fn_call_width = 100

macro_rules! foo {
    () => {{
        // max_width = 96
        // fn_call_width = 100

        // WARNING: `fn_call_width` cannot have a value that exceeds `max_width`. `fn_call_width` will be set to the same value as `max_width`
        // Which results in:
        // fn_call_width = 96
    }};
}