Auto merge of #4809 - iankronquist:patch-1, r=flip1995

[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 89398f82c9e5c702da57309eea22e2a176c2f478..dc5a58abe56d01117af2fa5fe327fc6ebaa0fa86 100644 (file)
--- a/clippy_lints/src/missing_const_for_fn.rs
+++ b/clippy_lints/src/missing_const_for_fn.rs
@@ -1,11 +1,13 @@
-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 crate::utils::{has_drop, is_entrypoint_fn, span_lint, trait_ref_of_method};
+use rustc::lint::in_external_macro;
+use rustc_hir as hir;
+use rustc_hir::intravisit::FnKind;
+use rustc_hir::{Body, Constness, FnDecl, HirId};
+use rustc_lint::{LateContext, LateLintPass};
 use rustc_mir::transform::qualify_min_const_fn::is_min_const_fn;
-use syntax_pos::Span;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::Span;
+use rustc_typeck::hir_ty_to_ty;
 
 declare_clippy_lint! {
     /// **What it does:**
@@ -74,8 +76,8 @@ fn check_fn(
         &mut self,
         cx: &LateContext<'_, '_>,
         kind: FnKind<'_>,
-        _: &FnDecl,
-        _: &Body,
+        _: &FnDecl<'_>,
+        _: &Body<'_>,
         span: Span,
         hir_id: HirId,
     ) {
@@ -94,7 +96,10 @@ fn check_fn(
                 }
             },
             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;
                 }
             },
@@ -104,16 +109,27 @@ fn check_fn(
         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 rustc_mir::const_eval::is_min_const_fn(cx.tcx, 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`");
         }
     }
 }
 
+/// 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 dropable, 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
 }