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Rollup merge of #78836 - fanzier:struct-and-slice-destructuring, r=petrochenkov

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Implement destructuring assignment for structs and slices

This is the second step towards implementing destructuring assignment (RFC: rust-lang/rfcs#2909, tracking issue: #71126). This PR is the second part of #71156, which was split up to allow for easier review.

Note that the first PR (#78748) is not merged yet, so it is included as the first commit in this one. I thought this would allow the review to start earlier because I have some time this weekend to respond to reviews. If ``@petrochenkov`` prefers to wait until the first PR is merged, I totally understand, of course.

This PR implements destructuring assignment for (tuple) structs and slices. In order to do this, the following *parser change* was necessary: struct expressions are not required to have a base expression, i.e. `Struct { a: 1, .. }` becomes legal (in order to act like a struct pattern).

Unfortunately, this PR slightly regresses the diagnostics implemented in #77283. However, it is only a missing help message in `src/test/ui/issues/issue-77218.rs`. Other instances of this diagnostic are not affected. Since I don't exactly understand how this help message works and how to fix it yet, I was hoping it's OK to regress this temporarily and fix it in a follow-up PR.

Thanks to ``@varkor`` who helped with the implementation, particularly around the struct rest changes.

r? ``@petrochenkov``
This commit is contained in:
Mara Bos 2020-11-12 19:46:09 +01:00 • committed by GitHub
commit 755dd14e00
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32 changed files with 619 additions and 108 deletions
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10
compiler/rustc_parse/src/parser/expr.rs
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@ -2087,7 +2087,7 @@ impl<'a> Parser<'a> {
recover: bool,
) -> PResult<'a, P<Expr>> {
let mut fields = Vec::new();
let mut base = None;
let mut base = ast::StructRest::None;
let mut recover_async = false;
attrs.extend(self.parse_inner_attributes()?);
@ -2102,8 +2102,14 @@ impl<'a> Parser<'a> {
while self.token != token::CloseDelim(token::Brace) {
if self.eat(&token::DotDot) {
let exp_span = self.prev_token.span;
// We permit `.. }` on the left-hand side of a destructuring assignment.
if self.check(&token::CloseDelim(token::Brace)) {
self.sess.gated_spans.gate(sym::destructuring_assignment, self.prev_token.span);
base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
break;
}
match self.parse_expr() {
Ok(e) => base = Some(e),
Ok(e) => base = ast::StructRest::Base(e),
Err(mut e) if recover => {
e.emit();
self.recover_stmt();