cargo/lints/rules/
blanket_hint_mostly_unused.rs

1use std::path::Path;
2
3use annotate_snippets::AnnotationKind;
4use annotate_snippets::Level;
5use annotate_snippets::Patch;
6use annotate_snippets::Snippet;
7use cargo_util_schemas::manifest::ProfilePackageSpec;
8use cargo_util_schemas::manifest::TomlToolLints;
9
10use crate::CargoResult;
11use crate::GlobalContext;
12use crate::core::MaybePackage;
13use crate::lints::Lint;
14use crate::lints::LintLevel;
15use crate::lints::get_key_value_span;
16use crate::lints::rel_cwd_manifest_path;
17
18pub const LINT: Lint = Lint {
19    name: "blanket_hint_mostly_unused",
20    desc: "blanket_hint_mostly_unused lint",
21    groups: &[],
22    default_level: LintLevel::Warn,
23    edition_lint_opts: None,
24    feature_gate: None,
25    docs: Some(
26        r#"
27### What it does
28Checks if `hint-mostly-unused` being applied to all dependencies.
29
30### Why it is bad
31`hint-mostly-unused` indicates that most of a crate's API surface will go
32unused by anything depending on it; this hint can speed up the build by
33attempting to minimize compilation time for items that aren't used at all.
34Misapplication to crates that don't fit that criteria will slow down the build
35rather than speeding it up. It should be selectively applied to dependencies
36that meet these criteria. Applying it globally is always a misapplication and
37will likely slow down the build.
38
39### Example
40```toml
41[profile.dev.package."*"]
42hint-mostly-unused = true
43```
44
45Should instead be:
46```toml
47[profile.dev.package.huge-mostly-unused-dependency]
48hint-mostly-unused = true
49```
50"#,
51    ),
52};
53
54pub fn blanket_hint_mostly_unused(
55    maybe_pkg: &MaybePackage,
56    path: &Path,
57    pkg_lints: &TomlToolLints,
58    error_count: &mut usize,
59    gctx: &GlobalContext,
60) -> CargoResult<()> {
61    let (lint_level, reason) = LINT.level(
62        pkg_lints,
63        maybe_pkg.edition(),
64        maybe_pkg.unstable_features(),
65    );
66
67    if lint_level == LintLevel::Allow {
68        return Ok(());
69    }
70
71    let level = lint_level.to_diagnostic_level();
72    let manifest_path = rel_cwd_manifest_path(path, gctx);
73    let mut paths = Vec::new();
74
75    if let Some(profiles) = maybe_pkg.profiles() {
76        for (profile_name, top_level_profile) in &profiles.0 {
77            if let Some(true) = top_level_profile.hint_mostly_unused {
78                paths.push((
79                    vec!["profile", profile_name.as_str(), "hint-mostly-unused"],
80                    true,
81                ));
82            }
83
84            if let Some(build_override) = &top_level_profile.build_override
85                && let Some(true) = build_override.hint_mostly_unused
86            {
87                paths.push((
88                    vec![
89                        "profile",
90                        profile_name.as_str(),
91                        "build-override",
92                        "hint-mostly-unused",
93                    ],
94                    false,
95                ));
96            }
97
98            if let Some(packages) = &top_level_profile.package
99                && let Some(profile) = packages.get(&ProfilePackageSpec::All)
100                && let Some(true) = profile.hint_mostly_unused
101            {
102                paths.push((
103                    vec![
104                        "profile",
105                        profile_name.as_str(),
106                        "package",
107                        "*",
108                        "hint-mostly-unused",
109                    ],
110                    false,
111                ));
112            }
113        }
114    }
115
116    for (i, (path, show_per_pkg_suggestion)) in paths.iter().enumerate() {
117        if lint_level.is_error() {
118            *error_count += 1;
119        }
120        let title = "`hint-mostly-unused` is being blanket applied to all dependencies";
121        let help_txt =
122            "scope `hint-mostly-unused` to specific packages with a lot of unused object code";
123        if let (Some(span), Some(table_span)) = (
124            get_key_value_span(maybe_pkg.document(), &path),
125            get_key_value_span(maybe_pkg.document(), &path[..path.len() - 1]),
126        ) {
127            let mut report = Vec::new();
128            let mut primary_group = level.clone().primary_title(title).element(
129                Snippet::source(maybe_pkg.contents())
130                    .path(&manifest_path)
131                    .annotation(
132                        AnnotationKind::Primary.span(table_span.key.start..table_span.key.end),
133                    )
134                    .annotation(AnnotationKind::Context.span(span.key.start..span.value.end)),
135            );
136
137            if *show_per_pkg_suggestion {
138                report.push(
139                    Level::HELP.secondary_title(help_txt).element(
140                        Snippet::source(maybe_pkg.contents())
141                            .path(&manifest_path)
142                            .patch(Patch::new(
143                                table_span.key.end..table_span.key.end,
144                                ".package.<pkg_name>",
145                            )),
146                    ),
147                );
148            } else {
149                primary_group = primary_group.element(Level::HELP.message(help_txt));
150            }
151
152            if i == 0 {
153                primary_group = primary_group
154                    .element(Level::NOTE.message(LINT.emitted_source(lint_level, reason)));
155            }
156
157            // The primary group should always be first
158            report.insert(0, primary_group);
159
160            gctx.shell().print_report(&report, lint_level.force())?;
161        }
162    }
163
164    Ok(())
165}
cargo/lints/rules/blanket_hint_mostly_unused.rs

cargo/lints/rules/
blanket_hint_mostly_unused.rs
