Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Fix missing_const_for_fn false positive #4450

Merged
merged 2 commits into from Aug 29, 2019
Merged
Show file tree
Hide file tree
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
@@ -1,10 +1,11 @@
use crate::utils::{is_entrypoint_fn, span_lint, trait_ref_of_method};
use crate::utils::{has_drop, 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::hir::{Body, Constness, FnDecl, HirId, HirVec};
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 rustc_typeck::hir_ty_to_ty;
use syntax_pos::Span;

declare_clippy_lint! {
@@ -94,7 +95,10 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingConstForFn {
}
},
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;
}
},
@@ -113,6 +117,16 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingConstForFn {
}
}

/// 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: &HirVec<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`
fn already_const(header: hir::FnHeader) -> bool {
header.constness == Constness::Const
@@ -68,3 +68,25 @@ impl std::ops::Add for Point {
Point(self.0 + other.0, self.1 + other.1)
}
}

mod with_drop {
pub struct A;
pub struct B;
impl Drop for A {
fn drop(&mut self) {}
}

impl A {
// This can not be const because the type implements `Drop`.
pub fn a(self) -> B {
B
}
}
phansch marked this conversation as resolved.
Show resolved Hide resolved

impl B {
// This can not be const because `a` implements `Drop`.
pub fn a(self, a: A) -> B {
B
}
}
}
@@ -53,5 +53,20 @@ fn generic_arr<T: Copy>(t: [T; 1]) -> T {
t[0]
}

mod with_drop {
pub struct A;
pub struct B;
impl Drop for A {
fn drop(&mut self) {}
}

impl B {
// This can be const, because `a` is passed by reference
pub fn b(self, a: &A) -> B {
B
}
}
}

// Should not be const
fn main() {}
@@ -49,5 +49,13 @@ LL | | t
LL | | }
| |_^

error: aborting due to 6 previous errors
error: this could be a const_fn
--> $DIR/could_be_const.rs:65:9
|
LL | / pub fn b(self, a: &A) -> B {
LL | | B
LL | | }
| |_________^

error: aborting due to 7 previous errors