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Auto merge of #6077 - ebroto:revert_or_fun_call_const, r=matthiaskrgr

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Revert: or_fun_call should lint calls to `const fn`s with no args

The changes in #5889 and #5984 were done under the incorrect assumption that a `const fn` with no args was guaranteed to be evaluated at compile time.  A `const fn` is only guaranteed to be evaluated at compile time if it's inside a const context (the initializer of a `const` or a `static`).

See this [zulip conversation](https://rust-lang.zulipchat.com/#narrow/stream/122651-general/topic/Common.20misconception.3A.20.60const.20fn.60.20and.20its.20effect.20on.20codegen/near/208059113) for more details on this common misconception.

Given that none of the linted methods by `or_fun_call` can be called in const contexts, the lint should make no exceptions.

changelog: [`or_fun_call`] lints again calls to `const fn` with no args
This commit is contained in:
bors 2020-09-24 14:14:53 +00:00
commit cc1998f7b3
4 changed files with 28 additions and 51 deletions
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9
clippy_lints/src/utils/mod.rs
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@ -46,7 +46,6 @@
use rustc_middle::hir::map::Map;
use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
use rustc_middle::ty::{self, layout::IntegerExt, Ty, TyCtxt, TypeFoldable};
use rustc_mir::const_eval;
use rustc_span::hygiene::{ExpnKind, MacroKind};
use rustc_span::source_map::original_sp;
use rustc_span::symbol::{self, kw, Symbol};
@ -883,19 +882,11 @@ pub fn is_copy<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
/// Checks if an expression is constructing a tuple-like enum variant or struct
pub fn is_ctor_or_promotable_const_function(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
fn has_no_arguments(cx: &LateContext<'_>, def_id: DefId) -> bool {
cx.tcx.fn_sig(def_id).skip_binder().inputs().is_empty()
}
if let ExprKind::Call(ref fun, _) = expr.kind {
if let ExprKind::Path(ref qp) = fun.kind {
let res = cx.qpath_res(qp, fun.hir_id);
return match res {
def::Res::Def(DefKind::Variant | DefKind::Ctor(..), ..) => true,
// FIXME: check the constness of the arguments, see https://github.com/rust-lang/rust-clippy/pull/5682#issuecomment-638681210
def::Res::Def(DefKind::Fn | DefKind::AssocFn, def_id) if has_no_arguments(cx, def_id) => {
const_eval::is_const_fn(cx.tcx, def_id)
},
def::Res::Def(_, def_id) => cx.tcx.is_promotable_const_fn(def_id),
_ => false,
};

25
tests/ui/or_fun_call.fixed
View File

@ -58,6 +58,12 @@ fn or_fun_call() {
let without_default = Some(Foo);
without_default.unwrap_or_else(Foo::new);
let mut map = HashMap::<u64, String>::new();
map.entry(42).or_insert_with(String::new);
let mut btree = BTreeMap::<u64, String>::new();
btree.entry(42).or_insert_with(String::new);
let stringy = Some(String::from(""));
let _ = stringy.unwrap_or_else(|| "".to_owned());
@ -110,23 +116,4 @@ fn f() -> Option<()> {
Some(())
}
// Issue 5886 - const fn (with no arguments)
pub fn skip_const_fn_with_no_args() {
const fn foo() -> Option<i32> {
Some(42)
}
let _ = None.or(foo());
// See issue #5693.
let mut map = std::collections::HashMap::new();
map.insert(1, vec![1]);
map.entry(1).or_insert(vec![]);
let mut map = HashMap::<u64, String>::new();
map.entry(42).or_insert(String::new());
let mut btree = BTreeMap::<u64, String>::new();
btree.entry(42).or_insert(String::new());
}
fn main() {}

25
tests/ui/or_fun_call.rs
View File

@ -58,6 +58,12 @@ fn make<T>() -> T {
let without_default = Some(Foo);
without_default.unwrap_or(Foo::new());
let mut map = HashMap::<u64, String>::new();
map.entry(42).or_insert(String::new());
let mut btree = BTreeMap::<u64, String>::new();
btree.entry(42).or_insert(String::new());
let stringy = Some(String::from(""));
let _ = stringy.unwrap_or("".to_owned());
@ -110,23 +116,4 @@ fn f() -> Option<()> {
Some(())
}
// Issue 5886 - const fn (with no arguments)
pub fn skip_const_fn_with_no_args() {
const fn foo() -> Option<i32> {
Some(42)
}
let _ = None.or(foo());
// See issue #5693.
let mut map = std::collections::HashMap::new();
map.insert(1, vec![1]);
map.entry(1).or_insert(vec![]);
let mut map = HashMap::<u64, String>::new();
map.entry(42).or_insert(String::new());
let mut btree = BTreeMap::<u64, String>::new();
btree.entry(42).or_insert(String::new());
}
fn main() {}

20
tests/ui/or_fun_call.stderr
View File

@ -60,23 +60,35 @@ error: use of `unwrap_or` followed by a function call
LL | without_default.unwrap_or(Foo::new());
| ^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(Foo::new)`
error: use of `or_insert` followed by a function call
--> $DIR/or_fun_call.rs:62:19
|
LL | map.entry(42).or_insert(String::new());
| ^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `or_insert_with(String::new)`
error: use of `or_insert` followed by a function call
--> $DIR/or_fun_call.rs:65:21
|
LL | btree.entry(42).or_insert(String::new());
| ^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `or_insert_with(String::new)`
error: use of `unwrap_or` followed by a function call
--> $DIR/or_fun_call.rs:62:21
--> $DIR/or_fun_call.rs:68:21
|
LL | let _ = stringy.unwrap_or("".to_owned());
| ^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| "".to_owned())`
error: use of `or` followed by a function call
--> $DIR/or_fun_call.rs:87:35
--> $DIR/or_fun_call.rs:93:35
|
LL | let _ = Some("a".to_string()).or(Some("b".to_string()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `or_else(|| Some("b".to_string()))`
error: use of `or` followed by a function call
--> $DIR/or_fun_call.rs:91:10
--> $DIR/or_fun_call.rs:97:10
|
LL | .or(Some(Bar(b, Duration::from_secs(2))));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `or_else(|| Some(Bar(b, Duration::from_secs(2))))`
error: aborting due to 13 previous errors
error: aborting due to 15 previous errors