alint_rules/
line_max_width.rs

1//! `line_max_width` — cap on characters per line.
2//!
3//! Counts Unicode scalar values (chars) per line, not bytes or
4//! display cells. CJK, combining marks, and emoji that occupy
5//! two terminal columns count as one char — if you want real
6//! display-width accounting, use a formatter (Biome, prettier);
7//! that's out of alint's byte/structure scope.
8//!
9//! Check-only: truncation isn't a safe auto-fix. Users either
10//! refactor the line or widen the limit.
11
12use std::path::Path;
13
14use alint_core::{
15    Context, Error, Level, PerFileRule, Result, Rule, RuleSpec, Scope, ScopeFilter, Violation,
16};
17use serde::Deserialize;
18
19#[derive(Debug, Deserialize)]
20#[serde(deny_unknown_fields)]
21struct Options {
22    max_width: usize,
23}
24
25#[derive(Debug)]
26pub struct LineMaxWidthRule {
27    id: String,
28    level: Level,
29    policy_url: Option<String>,
30    message: Option<String>,
31    scope: Scope,
32    scope_filter: Option<ScopeFilter>,
33    max_width: usize,
34}
35
36impl Rule for LineMaxWidthRule {
37    fn id(&self) -> &str {
38        &self.id
39    }
40    fn level(&self) -> Level {
41        self.level
42    }
43    fn policy_url(&self) -> Option<&str> {
44        self.policy_url.as_deref()
45    }
46
47    fn evaluate(&self, ctx: &Context<'_>) -> Result<Vec<Violation>> {
48        let mut violations = Vec::new();
49        for entry in ctx.index.files() {
50            if !self.scope.matches(&entry.path) {
51                continue;
52            }
53            if let Some(filter) = &self.scope_filter
54                && !filter.matches(&entry.path, ctx.index)
55            {
56                continue;
57            }
58            let full = ctx.root.join(&entry.path);
59            let Ok(bytes) = std::fs::read(&full) else {
60                continue;
61            };
62            violations.extend(self.evaluate_file(ctx, &entry.path, &bytes)?);
63        }
64        Ok(violations)
65    }
66
67    fn as_per_file(&self) -> Option<&dyn PerFileRule> {
68        Some(self)
69    }
70
71    fn scope_filter(&self) -> Option<&ScopeFilter> {
72        self.scope_filter.as_ref()
73    }
74}
75
76impl PerFileRule for LineMaxWidthRule {
77    fn path_scope(&self) -> &Scope {
78        &self.scope
79    }
80
81    fn evaluate_file(
82        &self,
83        _ctx: &Context<'_>,
84        path: &Path,
85        bytes: &[u8],
86    ) -> Result<Vec<Violation>> {
87        // `chars().count()` requires a UTF-8-validated `&str` —
88        // line widths count Unicode scalars, not bytes. Non-UTF-8
89        // files silently skip, matching the rule-major path.
90        let Ok(text) = std::str::from_utf8(bytes) else {
91            return Ok(Vec::new());
92        };
93        let Some((line_no, width)) = first_overlong_line(text, self.max_width) else {
94            return Ok(Vec::new());
95        };
96        let msg = self.message.clone().unwrap_or_else(|| {
97            format!(
98                "line {line_no} is {width} chars wide; max is {}",
99                self.max_width
100            )
101        });
102        Ok(vec![
103            Violation::new(msg)
104                .with_path(std::sync::Arc::<Path>::from(path))
105                .with_location(line_no, self.max_width + 1),
106        ])
107    }
108}
109
110fn first_overlong_line(text: &str, max_width: usize) -> Option<(usize, usize)> {
111    for (idx, line) in text.split('\n').enumerate() {
112        let trimmed = line.strip_suffix('\r').unwrap_or(line);
113        let width = trimmed.chars().count();
114        if width > max_width {
115            return Some((idx + 1, width));
116        }
117    }
118    None
119}
120
121pub fn build(spec: &RuleSpec) -> Result<Box<dyn Rule>> {
122    let paths = spec
123        .paths
124        .as_ref()
125        .ok_or_else(|| Error::rule_config(&spec.id, "line_max_width requires a `paths` field"))?;
126    let opts: Options = spec
127        .deserialize_options()
128        .map_err(|e| Error::rule_config(&spec.id, format!("invalid options: {e}")))?;
129    if opts.max_width == 0 {
130        return Err(Error::rule_config(
131            &spec.id,
132            "line_max_width `max_width` must be > 0",
133        ));
134    }
135    if spec.fix.is_some() {
136        return Err(Error::rule_config(
137            &spec.id,
138            "line_max_width has no fix op — truncation is unsafe",
139        ));
140    }
141    Ok(Box::new(LineMaxWidthRule {
142        id: spec.id.clone(),
143        level: spec.level,
144        policy_url: spec.policy_url.clone(),
145        message: spec.message.clone(),
146        scope: Scope::from_paths_spec(paths)?,
147        scope_filter: spec.parse_scope_filter()?,
148        max_width: opts.max_width,
149    }))
150}
151
152#[cfg(test)]
153mod tests {
154    use super::*;
155
156    #[test]
157    fn short_file_is_ok() {
158        assert_eq!(first_overlong_line("hi\nthere\n", 10), None);
159    }
160
161    #[test]
162    fn flags_first_overlong_line() {
163        let txt = "short\nway too looooong for ten\nok\n";
164        // "way too looooong for ten" is 24 chars.
165        assert_eq!(first_overlong_line(txt, 10), Some((2, 24)));
166    }
167
168    #[test]
169    fn width_exactly_at_limit_is_ok() {
170        assert_eq!(first_overlong_line("0123456789\n", 10), None);
171    }
172
173    #[test]
174    fn crlf_is_stripped_before_counting() {
175        // "hi\r\n" should count as 2 chars ("hi"), not 3.
176        assert_eq!(first_overlong_line("hi\r\n", 2), None);
177    }
178
179    #[test]
180    fn counts_unicode_scalar_values_not_bytes() {
181        // "☃☃☃" is 3 scalars / 9 bytes. Under `max_width: 3` it's fine.
182        assert_eq!(first_overlong_line("☃☃☃\n", 3), None);
183        // Under max_width: 2 it's flagged.
184        assert_eq!(first_overlong_line("☃☃☃\n", 2), Some((1, 3)));
185    }
186}
alint_rules/line_max_width.rs

alint_rules/
line_max_width.rs
