Files
rust/src/libsyntax_pos
bors 6d523ee501 Auto merge of #66507 - ecstatic-morse:const-if-match, r=oli-obk
Enable `if` and `match` in constants behind a feature flag

This PR is an initial implementation of #49146. It introduces a `const_if_match` feature flag and does the following if it is enabled:
- Allows `Downcast` projections, `SwitchInt` terminators and `FakeRead`s for matched places through the MIR const-checker.
- Allows `if` and `match` expressions through the HIR const-checker.
- Stops converting `&&` to `&` and `||` to `|` in `const` and `static` items.

As a result, the following operations are now allowed in a const context behind the feature flag:
- `if` and `match`
- short circuiting logic operators (`&&` and `||`)
- the `assert` and `debug_assert` macros (if the `const_panic` feature flag is also enabled)

However, the following operations remain forbidden:
- `while`, `loop` and `for` (see #52000)
- the `?` operator (calls `From::from` on its error variant)
- the `assert_eq` and `assert_ne` macros, along with their `debug` variants (calls `fmt::Debug`)

This PR is possible now that we use dataflow for const qualification (see #64470 and #66385).

r? @oli-obk
cc @rust-lang/wg-const-eval @eddyb
2019-11-23 01:13:41 +00:00
..
2019-11-15 08:38:31 -05:00
2019-10-15 21:12:05 +01:00
2019-11-15 08:38:31 -05:00
2019-11-15 08:21:23 -05:00
2019-11-17 22:37:13 +01:00
2019-11-15 08:45:43 -05:00