clippy: allow default_hash_types on bootstrap

[rust.git] / clippy_lints / src / missing_const_for_fn.rs

diff --git a/clippy_lints/src/missing_const_for_fn.rs b/clippy_lints/src/missing_const_for_fn.rs
index 54f34d64eb50329bd1f9ac2bf98443a79775643a..59cbc481ed42eccd73758fe2d314b09bde109bff 100644 (file)
--- a/clippy_lints/src/missing_const_for_fn.rs
+++ b/clippy_lints/src/missing_const_for_fn.rs
@@ -1,11 +1,16 @@
-use crate::utils::{is_entrypoint_fn, span_lint, trait_ref_of_method};
-use rustc::hir;
-use rustc::hir::intravisit::FnKind;
-use rustc::hir::{Body, Constness, FnDecl, HirId};
-use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintPass};
-use rustc::{declare_lint_pass, declare_tool_lint};
-use rustc_mir::transform::qualify_min_const_fn::is_min_const_fn;
-use syntax_pos::Span;
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::qualify_min_const_fn::is_min_const_fn;
+use clippy_utils::ty::has_drop;
+use clippy_utils::{fn_has_unsatisfiable_preds, is_entrypoint_fn, meets_msrv, msrvs, trait_ref_of_method};
+use rustc_hir as hir;
+use rustc_hir::intravisit::FnKind;
+use rustc_hir::{Body, Constness, FnDecl, GenericParamKind, HirId};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_semver::RustcVersion;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::Span;
+use rustc_typeck::hir_ty_to_ty;
 
 declare_clippy_lint! {
     /// **What it does:**
@@ -40,70 +45,120 @@
     /// **Example:**
     ///
     /// ```rust
+    /// # struct Foo {
+    /// #     random_number: usize,
+    /// # }
+    /// # impl Foo {
     /// fn new() -> Self {
     ///     Self { random_number: 42 }
     /// }
+    /// # }
     /// ```
     ///
     /// Could be a const fn:
     ///
     /// ```rust
+    /// # struct Foo {
+    /// #     random_number: usize,
+    /// # }
+    /// # impl Foo {
     /// const fn new() -> Self {
     ///     Self { random_number: 42 }
     /// }
+    /// # }
     /// ```
     pub MISSING_CONST_FOR_FN,
     nursery,
     "Lint functions definitions that could be made `const fn`"
 }
 
-declare_lint_pass!(MissingConstForFn => [MISSING_CONST_FOR_FN]);
+impl_lint_pass!(MissingConstForFn => [MISSING_CONST_FOR_FN]);
 
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingConstForFn {
+pub struct MissingConstForFn {
+    msrv: Option<RustcVersion>,
+}
+
+impl MissingConstForFn {
+    #[must_use]
+    pub fn new(msrv: Option<RustcVersion>) -> Self {
+        Self { msrv }
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for MissingConstForFn {
     fn check_fn(
         &mut self,
-        cx: &LateContext<'_, '_>,
+        cx: &LateContext<'_>,
         kind: FnKind<'_>,
-        _: &FnDecl,
-        _: &Body,
+        _: &FnDecl<'_>,
+        _: &Body<'_>,
         span: Span,
         hir_id: HirId,
     ) {
-        let def_id = cx.tcx.hir().local_def_id_from_hir_id(hir_id);
+        if !meets_msrv(self.msrv.as_ref(), &msrvs::CONST_IF_MATCH) {
+            return;
+        }
 
-        if in_external_macro(cx.tcx.sess, span) || is_entrypoint_fn(cx, def_id) {
+        let def_id = cx.tcx.hir().local_def_id(hir_id);
+
+        if in_external_macro(cx.tcx.sess, span) || is_entrypoint_fn(cx, def_id.to_def_id()) {
+            return;
+        }
+
+        // Building MIR for `fn`s with unsatisfiable preds results in ICE.
+        if fn_has_unsatisfiable_preds(cx, def_id.to_def_id()) {
             return;
         }
 
         // Perform some preliminary checks that rule out constness on the Clippy side. This way we
         // can skip the actual const check and return early.
         match kind {
-            FnKind::ItemFn(_, _, header, ..) => {
-                if already_const(header) {
+            FnKind::ItemFn(_, generics, header, ..) => {
+                let has_const_generic_params = generics
+                    .params
+                    .iter()
+                    .any(|param| matches!(param.kind, GenericParamKind::Const { .. }));
+
+                if already_const(header) || has_const_generic_params {
                     return;
                 }
             },
             FnKind::Method(_, sig, ..) => {
-                if trait_ref_of_method(cx, hir_id).is_some() || already_const(sig.header) {
+                if trait_ref_of_method(cx, hir_id).is_some()
+                    || already_const(sig.header)
+                    || method_accepts_dropable(cx, sig.decl.inputs)
+                {
                     return;
                 }
             },
-            _ => return,
+            FnKind::Closure => return,
         }
 
         let mir = cx.tcx.optimized_mir(def_id);
 
-        if let Err((span, err)) = is_min_const_fn(cx.tcx, def_id, &mir) {
-            if cx.tcx.is_min_const_fn(def_id) {
+        if let Err((span, err)) = is_min_const_fn(cx.tcx, mir, self.msrv.as_ref()) {
+            if cx.tcx.is_const_fn_raw(def_id.to_def_id()) {
                 cx.tcx.sess.span_err(span, &err);
             }
         } else {
-            span_lint(cx, MISSING_CONST_FOR_FN, span, "this could be a const_fn");
+            span_lint(cx, MISSING_CONST_FOR_FN, span, "this could be a `const fn`");
         }
     }
+    extract_msrv_attr!(LateContext);
+}
+
+/// Returns true if any of the method parameters is a type that implements `Drop`. The method
+/// can't be made const then, because `drop` can't be const-evaluated.
+fn method_accepts_dropable(cx: &LateContext<'_>, param_tys: &[hir::Ty<'_>]) -> bool {
+    // If any of the params are droppable, return true
+    param_tys.iter().any(|hir_ty| {
+        let ty_ty = hir_ty_to_ty(cx.tcx, hir_ty);
+        has_drop(cx, ty_ty)
+    })
 }
 
 // We don't have to lint on something that's already `const`
+#[must_use]
 fn already_const(header: hir::FnHeader) -> bool {
     header.constness == Constness::Const
 }