Add a lint to warn on `T: Drop` bounds
**What it does:** Checks for generics with `std::ops::Drop` as bounds.
**Why is this bad?** `Drop` bounds do not really accomplish anything.
A type may have compiler-generated drop glue without implementing the
`Drop` trait itself. The `Drop` trait also only has one method,
`Drop::drop`, and that function is by fiat not callable in user code.
So there is really no use case for using `Drop` in trait bounds.
**Known problems:** None.
**Example:**
```rust
fn foo<T: Drop>() {}
```
Fixes#3773
Update why transmute_int_to_float is bad
As suggested in #3550, this PR changes the reason why using `transmute` from an integer to a float is not recommended. Effectively, `from_bits` uses `transmute` underneath, but the former is preferred.
**What it does:** Checks for generics with `std::ops::Drop` as bounds.
**Why is this bad?** `Drop` bounds do not really accomplish anything.
A type may have compiler-generated drop glue without implementing the
`Drop` trait itself. The `Drop` trait also only has one method,
`Drop::drop`, and that function is by fiat not callable in user code.
So there is really no use case for using `Drop` in trait bounds.
**Known problems:** None.
**Example:**
```rust
fn foo<T: Drop>() {}
```
Fix ICE #3717 in lint implicit_hasher
Fixes#3717
This fixes the ICE. We lose some information in a very specific case though. But less information if better than an ICE. For an example see the test file.
Does anyone know, if there's another way to get the `ty::Ty` of a `hir::Expr`?
Fix ICE in needless_pass_by_value lint
If I understand it correctly, we were first creating a type with a
`RegionKind::ReErased` region and then deleted it again in
`util::implements_trait` with:
cx.tcx.erase_regions(&ty);
causing the type query to fail.
It looks like using `ReEmpty` works around that deletion.
Fixes#3144
Macro check for assertion_on_constants lint
The `assertion_on_constants` lint currently has following output for this code [Playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=6f2c9df6fc50baf847212d3b5136ee97):
```rust
macro_rules! assert_const {
($len:expr) => {
assert!($len > 0);
}
}
fn main() {
assert_const!(3);
assert_const!(-1);
}
```
```
warning: assert!(const: true) will be optimized out by the compiler
--> src/main.rs:3:9
|
3 | assert!($len > 0);
| ^^^^^^^^^^^^^^^^^^
...
8 | assert_const!(3);
| ---------------- in this macro invocation
|
= note: #[warn(clippy::assertions_on_constants)] on by default
= help: remove it
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#assertions_on_constants
warning: assert!(const: false) should probably be replaced
--> src/main.rs:3:9
|
3 | assert!($len > 0);
| ^^^^^^^^^^^^^^^^^^
...
9 | assert_const!(-1);
| ----------------- in this macro invocation
|
= help: use panic!() or unreachable!()
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#assertions_on_constants
```
This is contradictory. This lint should not trigger if the `assert!` is in a macro itself.
Add a uitest subcommand to simplify UI test invocation
This makes running single tests a lot easier.
It's now
`TESTNAME=xxx cargo uitest`
instead of
`TESTNAME=xxx cargo test --test compile-test`
