cargo/diagnostics/rules/
unused_dependencies.rs

1use std::path::Path;
2
3use cargo_util_schemas::manifest::TomlPackageBuild;
4use cargo_util_schemas::manifest::TomlToolLints;
5use cargo_util_terminal::report::AnnotationKind;
6use cargo_util_terminal::report::Group;
7use cargo_util_terminal::report::Level;
8use cargo_util_terminal::report::Origin;
9use cargo_util_terminal::report::Patch;
10use cargo_util_terminal::report::Snippet;
11use tracing::instrument;
12
13use super::STYLE;
14use crate::CargoResult;
15use crate::GlobalContext;
16use crate::core::Package;
17use crate::diagnostics::DiagnosticStats;
18use crate::diagnostics::Lint;
19use crate::diagnostics::LintLevel;
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 fn unused_build_dependencies_no_build_rs(
88    pkg: &Package,
89    manifest_path: &Path,
90    cargo_lints: &TomlToolLints,
91    stats: &mut DiagnosticStats,
92    gctx: &GlobalContext,
93) -> CargoResult<()> {
94    let (lint_level, reason) = LINT.level(
95        cargo_lints,
96        pkg.rust_version(),
97        pkg.manifest().unstable_features(),
98    );
99
100    if lint_level == LintLevel::Allow {
101        return Ok(());
102    }
103
104    let manifest_path = rel_cwd_manifest_path(manifest_path, gctx);
105
106    let manifest = pkg.manifest();
107    let Some(package) = &manifest.normalized_toml().package else {
108        return Ok(());
109    };
110    if package.build != Some(TomlPackageBuild::Auto(false)) {
111        return Ok(());
112    }
113
114    let document = manifest.document();
115    let contents = manifest.contents();
116
117    for (i, dep_name) in manifest
118        .normalized_toml()
119        .build_dependencies()
120        .iter()
121        .flat_map(|m| m.keys())
122        .enumerate()
123    {
124        let level = lint_level.to_diagnostic_level();
125        let emitted_source = LINT.emitted_source(lint_level, reason);
126
127        let mut primary = Group::with_title(level.primary_title(LINT.desc));
128        if let Some(document) = document
129            && let Some(contents) = contents
130            && let Some(span) = get_key_value_span(document, &["build-dependencies", dep_name])
131        {
132            let span = span.key.start..span.value.end;
133            primary = primary.element(
134                Snippet::source(contents)
135                    .path(&manifest_path)
136                    .annotation(AnnotationKind::Primary.span(span)),
137            );
138        } else {
139            primary = primary.element(Origin::path(&manifest_path));
140        }
141        if i == 0 {
142            primary = primary.element(Level::NOTE.message(emitted_source));
143        }
144        let mut report = vec![primary];
145        if let Some(document) = document
146            && let Some(contents) = contents
147            && let Some(span) = get_key_value_span(document, &["build-dependencies", dep_name])
148        {
149            let span = span.key.start..span.value.end;
150            let mut help = Group::with_title(Level::HELP.secondary_title("remove the dependency"));
151            help = help.element(
152                Snippet::source(contents)
153                    .path(&manifest_path)
154                    .patch(Patch::new(span, "")),
155            );
156            report.push(help);
157        }
158
159        stats.record_lint(lint_level);
160        gctx.shell().print_report(&report, lint_level.force())?;
161    }
162
163    Ok(())
164}
cargo/diagnostics/rules/unused_dependencies.rs

cargo/diagnostics/rules/
unused_dependencies.rs
