Add `crate_in_macro_def` lint

6 files changed, 106 insertions, 1 deletions

diff --git a/clippy_lints/src/crate_in_macro_def.rs b/clippy_lints/src/crate_in_macro_def.rs
new file mode 100644
index 00000000000..9ac6d6d520c
--- /dev/null
+++ b/clippy_lints/src/crate_in_macro_def.rs
@@ -0,0 +1,100 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use rustc_ast::ast::MacroDef;
+use rustc_ast::node_id::NodeId;
+use rustc_ast::token::{Token, TokenKind};
+use rustc_ast::tokenstream::{TokenStream, TokenTree};
+use rustc_errors::Applicability;
+use rustc_lint::{EarlyContext, EarlyLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::Span;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for use of `crate` as opposed to `$crate` in a macro definition.
+    ///
+    /// ### Why is this bad?
+    /// `crate` refers to macro call's crate, whereas `$crate` refers to the macro
+    /// definition's crate. Rarely is the former intended. See:
+    /// https://doc.rust-lang.org/reference/macros-by-example.html#hygiene
+    ///
+    /// ### Example
+    /// ```rust
+    /// macro_rules! print_message {
+    ///     () => {
+    ///         println!("{}", crate::MESSAGE);
+    ///     };
+    /// }
+    /// pub const MESSAGE: &str = "Hello!";
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// macro_rules! print_message {
+    ///     () => {
+    ///         println!("{}", $crate::MESSAGE);
+    ///     };
+    /// }
+    /// pub const MESSAGE: &str = "Hello!";
+    /// ```
+    #[clippy::version = "1.61.0"]
+    pub CRATE_IN_MACRO_DEF,
+    correctness,
+    "using `crate` in a macro definition"
+}
+declare_lint_pass!(CrateInMacroDef => [CRATE_IN_MACRO_DEF]);
+
+impl EarlyLintPass for CrateInMacroDef {
+    fn check_mac_def(&mut self, cx: &EarlyContext<'_>, macro_def: &MacroDef, _: NodeId) {
+        let tts = macro_def.body.inner_tokens();
+        if let Some(span) = contains_unhygienic_crate_reference(&tts) {
+            span_lint_and_sugg(
+                cx,
+                CRATE_IN_MACRO_DEF,
+                span,
+                "reference to the macro call's crate, which is rarely intended",
+                "if reference to the macro definition's crate is intended, use",
+                String::from("$crate"),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+}
+
+fn contains_unhygienic_crate_reference(tts: &TokenStream) -> Option<Span> {
+    let mut prev_is_dollar = false;
+    let mut cursor = tts.trees();
+    while let Some(curr) = cursor.next() {
+        if_chain! {
+            if !prev_is_dollar;
+            if let Some(span) = is_crate_keyword(&curr);
+            if let Some(next) = cursor.look_ahead(0);
+            if is_token(next, &TokenKind::ModSep);
+            then {
+                return Some(span);
+            }
+        }
+        if let TokenTree::Delimited(_, _, tts) = &curr {
+            let span = contains_unhygienic_crate_reference(tts);
+            if span.is_some() {
+                return span;
+            }
+        }
+        prev_is_dollar = is_token(&curr, &TokenKind::Dollar);
+    }
+    None
+}
+
+fn is_crate_keyword(tt: &TokenTree) -> Option<Span> {
+    if_chain! {
+        if let TokenTree::Token(Token { kind: TokenKind::Ident(symbol, _), span }) = tt;
+        if symbol.as_str() == "crate";
+        then { Some(*span) } else { None }
+    }
+}
+
+fn is_token(tt: &TokenTree, kind: &TokenKind) -> bool {
+    if let TokenTree::Token(Token { kind: other, .. }) = tt {
+        kind == other
+    } else {
+        false
+    }
+}
diff --git a/clippy_lints/src/lib.register_all.rs b/clippy_lints/src/lib.register_all.rs
index 132a4662676..1fb3ca1fd9b 100644
--- a/clippy_lints/src/lib.register_all.rs
+++ b/clippy_lints/src/lib.register_all.rs
@@ -37,6 +37,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(comparison_chain::COMPARISON_CHAIN),
     LintId::of(copies::IFS_SAME_COND),
     LintId::of(copies::IF_SAME_THEN_ELSE),
+    LintId::of(crate_in_macro_def::CRATE_IN_MACRO_DEF),
     LintId::of(default::FIELD_REASSIGN_WITH_DEFAULT),
     LintId::of(dereference::NEEDLESS_BORROW),
     LintId::of(derivable_impls::DERIVABLE_IMPLS),
diff --git a/clippy_lints/src/lib.register_correctness.rs b/clippy_lints/src/lib.register_correctness.rs
index df63f84463d..d5cade8fe99 100644
--- a/clippy_lints/src/lib.register_correctness.rs
+++ b/clippy_lints/src/lib.register_correctness.rs
@@ -16,6 +16,7 @@ store.register_group(true, "clippy::correctness", Some("clippy_correctness"), ve
     LintId::of(casts::CAST_SLICE_DIFFERENT_SIZES),
     LintId::of(copies::IFS_SAME_COND),
     LintId::of(copies::IF_SAME_THEN_ELSE),
+    LintId::of(crate_in_macro_def::CRATE_IN_MACRO_DEF),
     LintId::of(derive::DERIVE_HASH_XOR_EQ),
     LintId::of(derive::DERIVE_ORD_XOR_PARTIAL_ORD),
     LintId::of(drop_forget_ref::DROP_COPY),
diff --git a/clippy_lints/src/lib.register_lints.rs b/clippy_lints/src/lib.register_lints.rs
index 65ad64f1901..984939a74b8 100644
--- a/clippy_lints/src/lib.register_lints.rs
+++ b/clippy_lints/src/lib.register_lints.rs
@@ -97,6 +97,7 @@ store.register_lints(&[
     copies::IF_SAME_THEN_ELSE,
     copies::SAME_FUNCTIONS_IN_IF_CONDITION,
     copy_iterator::COPY_ITERATOR,
+    crate_in_macro_def::CRATE_IN_MACRO_DEF,
     create_dir::CREATE_DIR,
     dbg_macro::DBG_MACRO,
     default::DEFAULT_TRAIT_ACCESS,
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index f2a07999144..c8b57956b1b 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -190,6 +190,7 @@ mod collapsible_match;
 mod comparison_chain;
 mod copies;
 mod copy_iterator;
+mod crate_in_macro_def;
 mod create_dir;
 mod dbg_macro;
 mod default;
@@ -867,6 +868,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
             ignore_publish: cargo_ignore_publish,
         })
     });
+    store.register_early_pass(|| Box::new(crate_in_macro_def::CrateInMacroDef));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 
diff --git a/clippy_lints/src/utils/conf.rs b/clippy_lints/src/utils/conf.rs
index 680b2eb1da7..b1e474f8056 100644
--- a/clippy_lints/src/utils/conf.rs
+++ b/clippy_lints/src/utils/conf.rs
@@ -123,7 +123,7 @@ macro_rules! define_Conf {
 
         #[cfg(feature = "internal")]
         pub mod metadata {
-            use crate::utils::internal_lints::metadata_collector::ClippyConfiguration;
+            use $crate::utils::internal_lints::metadata_collector::ClippyConfiguration;
 
             macro_rules! wrap_option {
                 () => (None);