Add lint for statics with explicit static lifetime.

clippy_lints/src/lib.rs

@@ -256,6 +256,7 @@ pub mod returns;
 pub mod serde_api;
 pub mod shadow;
 pub mod slow_vector_initialization;
+pub mod static_static_lifetime;
 pub mod strings;
 pub mod suspicious_trait_impl;
 pub mod swap;
@@ -554,6 +555,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
     reg.register_late_lint_pass(box identity_conversion::IdentityConversion::default());
     reg.register_late_lint_pass(box types::ImplicitHasher);
     reg.register_early_lint_pass(box const_static_lifetime::StaticConst);
+    reg.register_early_lint_pass(box static_static_lifetime::StaticStatic);
     reg.register_late_lint_pass(box fallible_impl_from::FallibleImplFrom);
     reg.register_late_lint_pass(box replace_consts::ReplaceConsts);
     reg.register_late_lint_pass(box types::UnitArg);
@@ -844,6 +846,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
         returns::UNUSED_UNIT,
         serde_api::SERDE_API_MISUSE,
         slow_vector_initialization::SLOW_VECTOR_INITIALIZATION,
+        static_static_lifetime::STATIC_STATIC_LIFETIME,
         strings::STRING_LIT_AS_BYTES,
         suspicious_trait_impl::SUSPICIOUS_ARITHMETIC_IMPL,
         suspicious_trait_impl::SUSPICIOUS_OP_ASSIGN_IMPL,
@@ -962,6 +965,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
         returns::LET_AND_RETURN,
         returns::NEEDLESS_RETURN,
         returns::UNUSED_UNIT,
+        static_static_lifetime::STATIC_STATIC_LIFETIME,
         strings::STRING_LIT_AS_BYTES,
         types::FN_TO_NUMERIC_CAST,
         types::FN_TO_NUMERIC_CAST_WITH_TRUNCATION,

clippy_lints/src/static_static_lifetime.rs

@@ -0,0 +1,93 @@
+use crate::utils::{in_macro_or_desugar, snippet, span_lint_and_then};
+use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
+use rustc::{declare_lint_pass, declare_tool_lint};
+use rustc_errors::Applicability;
+use syntax::ast::*;
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for statics with an explicit `'static` lifetime.
+    ///
+    /// **Why is this bad?** Adding `'static` to every reference can create very
+    /// complicated types.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```ignore
+    /// static FOO: &'static [(&'static str, &'static str, fn(&Bar) -> bool)] =
+    /// &[...]
+    /// ```
+    /// This code can be rewritten as
+    /// ```ignore
+    ///  static FOO: &[(&str, &str, fn(&Bar) -> bool)] = &[...]
+    /// ```
+    pub STATIC_STATIC_LIFETIME,
+    style,
+    "Using explicit `'static` lifetime for statics when elision rules would allow omitting them."
+}
+
+declare_lint_pass!(StaticStatic => [STATIC_STATIC_LIFETIME]);
+
+impl StaticStatic {
+    // Recursively visit types
+    fn visit_type(&mut self, ty: &Ty, cx: &EarlyContext<'_>) {
+        match ty.node {
+            // Be careful of nested structures (arrays and tuples)
+            TyKind::Array(ref ty, _) => {
+                self.visit_type(&*ty, cx);
+            },
+            TyKind::Tup(ref tup) => {
+                for tup_ty in tup {
+                    self.visit_type(&*tup_ty, cx);
+                }
+            },
+            // This is what we are looking for !
+            TyKind::Rptr(ref optional_lifetime, ref borrow_type) => {
+                // Match the 'static lifetime
+                if let Some(lifetime) = *optional_lifetime {
+                    match borrow_type.ty.node {
+                        TyKind::Path(..) | TyKind::Slice(..) | TyKind::Array(..) | TyKind::Tup(..) => {
+                            if lifetime.ident.name == syntax::symbol::kw::StaticLifetime {
+                                let snip = snippet(cx, borrow_type.ty.span, "<type>");
+                                let sugg = format!("&{}", snip);
+                                span_lint_and_then(
+                                    cx,
+                                    STATIC_STATIC_LIFETIME,
+                                    lifetime.ident.span,
+                                    "Statics have by default a `'static` lifetime",
+                                    |db| {
+                                        db.span_suggestion(
+                                            ty.span,
+                                            "consider removing `'static`",
+                                            sugg,
+                                            Applicability::MachineApplicable, //snippet
+                                        );
+                                    },
+                                );
+                            }
+                        },
+                        _ => {},
+                    }
+                }
+                self.visit_type(&*borrow_type.ty, cx);
+            },
+            TyKind::Slice(ref ty) => {
+                self.visit_type(ty, cx);
+            },
+            _ => {},
+        }
+    }
+}
+
+impl EarlyLintPass for StaticStatic {
+    fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
+        if !in_macro_or_desugar(item.span) {
+            // Match only statics...
+            if let ItemKind::Static(ref var_type, _, _) = item.node {
+                self.visit_type(var_type, cx);
+            }
+        }
+    }
+
+    // Don't check associated consts because `'static` cannot be elided on those (issue #2438)
+}