cargo/diagnostics/rules/
unused_dependencies.rs

1use std::path::Path;
2
3use cargo_util_schemas::manifest::TomlPackageBuild;
4use cargo_util_terminal::report::AnnotationKind;
5use cargo_util_terminal::report::Group;
6use cargo_util_terminal::report::Level;
7use cargo_util_terminal::report::Origin;
8use cargo_util_terminal::report::Patch;
9use cargo_util_terminal::report::Snippet;
10use tracing::instrument;
11
12use super::STYLE;
13use crate::CargoResult;
14use crate::GlobalContext;
15use crate::core::Package;
16use crate::core::Workspace;
17use crate::diagnostics::DiagnosticStats;
18use crate::diagnostics::Lint;
19use crate::diagnostics::LintLevelProduct;
20use crate::diagnostics::get_key_value_span;
21use crate::diagnostics::rel_cwd_manifest_path;
22
23pub static LINT: &Lint = &Lint {
24    name: "unused_dependencies",
25    desc: "unused dependency",
26    primary_group: &STYLE,
27    msrv: Some(super::CARGO_LINTS_MSRV),
28    feature_gate: None,
29    docs: Some(
30        r#"
31### What it does
32
33Checks for dependencies that are not used by any of the cargo targets.
34
35### Why it is bad
36
37Slows down compilation time.
38
39### Drawbacks
40
41The lint is only emitted in specific circumstances as multiple cargo targets exist for the
42different dependencies tables and they must all be built to know if a dependency is unused.
43Currently, only the selected packages are checked and not all `path` dependencies like most lints.
44The cargo target selection flags,
45independent of which packages are selected, determine which dependencies tables are checked.
46As there is no way to select all cargo targets that use `[dev-dependencies]`,
47they are unchecked.
48
49Examples:
50- `cargo check` will lint `[build-dependencies]` and `[dependencies]`
51- `cargo check --all-targets` will still only lint `[build-dependencies]` and `[dependencies]` and not `[dev-dependencoes]`
52- `cargo check --bin foo` will not lint `[dependencies]` even if `foo` is the only bin though `[build-dependencies]` will be checked
53- `cargo check -p foo` will not lint any dependencies tables for the `path` dependency `bar` even if `bar` only has a `[lib]`
54
55There can be false positives when depending on a transitive dependency to activate a feature.
56
57For false positives from pinning the version of a transitive dependency in `Cargo.toml`,
58move the dependency to the `target."cfg(false)".dependencies` table.
59
60### Example
61
62```toml
63[package]
64name = "foo"
65
66[dependencies]
67unused = "1"
68```
69
70Should be written as:
71
72```toml
73[package]
74name = "foo"
75```
76"#,
77    ),
78};
79
80/// Lint for `[build-dependencies]` without a `build.rs`
81///
82/// These are always unused.
83///
84/// This must be determined independent of the compiler since there are no build targets to pass to
85/// rustc to report on these.
86#[instrument(skip_all)]
87pub(crate) fn lint_package(
88    _ws: &Workspace<'_>,
89    pkg: &Package,
90    manifest_path: &Path,
91    level: LintLevelProduct,
92    stats: &mut DiagnosticStats,
93    gctx: &GlobalContext,
94) -> CargoResult<()> {
95    let LintLevelProduct {
96        level: lint_level,
97        source,
98    } = level;
99
100    let manifest_path = rel_cwd_manifest_path(manifest_path, gctx);
101
102    let manifest = pkg.manifest();
103    let Some(package) = &manifest.normalized_toml().package else {
104        return Ok(());
105    };
106    if package.build != Some(TomlPackageBuild::Auto(false)) {
107        return Ok(());
108    }
109
110    let document = manifest.document();
111    let contents = manifest.contents();
112
113    for (i, dep_name) in manifest
114        .normalized_toml()
115        .build_dependencies()
116        .iter()
117        .flat_map(|m| m.keys())
118        .enumerate()
119    {
120        let level = lint_level.to_diagnostic_level();
121        let emitted_source = LINT.emitted_source(lint_level, source);
122
123        let mut primary = Group::with_title(level.primary_title(LINT.desc));
124        if let Some(document) = document
125            && let Some(contents) = contents
126            && let Some(span) = get_key_value_span(document, &["build-dependencies", dep_name])
127        {
128            let span = span.key.start..span.value.end;
129            primary = primary.element(
130                Snippet::source(contents)
131                    .path(&manifest_path)
132                    .annotation(AnnotationKind::Primary.span(span)),
133            );
134        } else {
135            primary = primary.element(Origin::path(&manifest_path));
136        }
137        if i == 0 {
138            primary = primary.element(Level::NOTE.message(emitted_source));
139        }
140        let mut report = vec![primary];
141        if let Some(document) = document
142            && let Some(contents) = contents
143            && let Some(span) = get_key_value_span(document, &["build-dependencies", dep_name])
144        {
145            let span = span.key.start..span.value.end;
146            let mut help = Group::with_title(Level::HELP.secondary_title("remove the dependency"));
147            help = help.element(
148                Snippet::source(contents)
149                    .path(&manifest_path)
150                    .patch(Patch::new(span, "")),
151            );
152            report.push(help);
153        }
154
155        stats.record_lint(lint_level);
156        gctx.shell().print_report(&report, lint_level.force())?;
157    }
158
159    Ok(())
160}
cargo/diagnostics/rules/unused_dependencies.rs

cargo/diagnostics/rules/
unused_dependencies.rs
