src/tools/clippy/clippy_lints/src/duplicate_mod.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use rustc_ast::ast::{Crate, Inline, Item, ItemKind, ModKind};
   3 use rustc_errors::MultiSpan;
   4 use rustc_lint::{EarlyContext, EarlyLintPass, Level, LintContext};
   5 use rustc_session::{declare_tool_lint, impl_lint_pass};
   6 use rustc_span::{FileName, Span};
   7 use std::collections::BTreeMap;
   8 use std::path::PathBuf;
   9
  10 declare_clippy_lint! {
  11     /// ### What it does
  12     /// Checks for files that are included as modules multiple times.
  13     ///
  14     /// ### Why is this bad?
  15     /// Loading a file as a module more than once causes it to be compiled
  16     /// multiple times, taking longer and putting duplicate content into the
  17     /// module tree.
  18     ///
  19     /// ### Example
  20     /// ```rust,ignore
  21     /// // lib.rs
  22     /// mod a;
  23     /// mod b;
  24     /// ```
  25     /// ```rust,ignore
  26     /// // a.rs
  27     /// #[path = "./b.rs"]
  28     /// mod b;
  29     /// ```
  30     ///
  31     /// Use instead:
  32     ///
  33     /// ```rust,ignore
  34     /// // lib.rs
  35     /// mod a;
  36     /// mod b;
  37     /// ```
  38     /// ```rust,ignore
  39     /// // a.rs
  40     /// use crate::b;
  41     /// ```
  42     #[clippy::version = "1.63.0"]
  43     pub DUPLICATE_MOD,
  44     suspicious,
  45     "file loaded as module multiple times"
  46 }
  47
  48 #[derive(PartialOrd, Ord, PartialEq, Eq)]
  49 struct Modules {
  50     local_path: PathBuf,
  51     spans: Vec<Span>,
  52     lint_levels: Vec<Level>,
  53 }
  54
  55 #[derive(Default)]
  56 pub struct DuplicateMod {
  57     /// map from the canonicalized path to `Modules`, `BTreeMap` to make the
  58     /// order deterministic for tests
  59     modules: BTreeMap<PathBuf, Modules>,
  60 }
  61
  62 impl_lint_pass!(DuplicateMod => [DUPLICATE_MOD]);
  63
  64 impl EarlyLintPass for DuplicateMod {
  65     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
  66         if let ItemKind::Mod(_, ModKind::Loaded(_, Inline::No, mod_spans)) = &item.kind
  67             && let FileName::Real(real) = cx.sess().source_map().span_to_filename(mod_spans.inner_span)
  68             && let Some(local_path) = real.into_local_path()
  69             && let Ok(absolute_path) = local_path.canonicalize()
  70         {
  71             let modules = self.modules.entry(absolute_path).or_insert(Modules {
  72                 local_path,
  73                 spans: Vec::new(),
  74                 lint_levels: Vec::new(),
  75             });
  76             modules.spans.push(item.span_with_attributes());
  77             modules.lint_levels.push(cx.get_lint_level(DUPLICATE_MOD));
  78         }
  79     }
  80
  81     fn check_crate_post(&mut self, cx: &EarlyContext<'_>, _: &Crate) {
  82         for Modules {
  83             local_path,
  84             spans,
  85             lint_levels,
  86         } in self.modules.values()
  87         {
  88             if spans.len() < 2 {
  89                 continue;
  90             }
  91
  92             // At this point the lint would be emitted
  93             assert_eq!(spans.len(), lint_levels.len());
  94             let spans: Vec<_> = spans
  95                 .iter()
  96                 .zip(lint_levels)
  97                 .filter_map(|(span, lvl)| {
  98                     if let Some(id) = lvl.get_expectation_id() {
  99                         cx.fulfill_expectation(id);
 100                     }
 101
 102                     (!matches!(lvl, Level::Allow | Level::Expect(_))).then_some(*span)
 103                 })
 104                 .collect();
 105
 106             if spans.len() < 2 {
 107                 continue;
 108             }
 109
 110             let mut multi_span = MultiSpan::from_spans(spans.clone());
 111             let (&first, duplicates) = spans.split_first().unwrap();
 112
 113             multi_span.push_span_label(first, "first loaded here");
 114             for &duplicate in duplicates {
 115                 multi_span.push_span_label(duplicate, "loaded again here");
 116             }
 117
 118             span_lint_and_help(
 119                 cx,
 120                 DUPLICATE_MOD,
 121                 multi_span,
 122                 &format!("file is loaded as a module multiple times: `{}`", local_path.display()),
 123                 None,
 124                 "replace all but one `mod` item with `use` items",
 125             );
 126         }
 127     }
 128 }