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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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21
compiler/rustc_ast_pretty/src/pprust/state.rs
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@ -1729,7 +1729,7 @@ impl<'a> State<'a> {
&mut self,
path: &ast::Path,
fields: &[ast::Field],
wth: &Option<P<ast::Expr>>,
rest: &ast::StructRest,
attrs: &[ast::Attribute],
) {
self.print_path(path, true, 0);
@ -1750,22 +1750,21 @@ impl<'a> State<'a> {
},
|f| f.span,
);
match *wth {
Some(ref expr) => {
match rest {
ast::StructRest::Base(_) | ast::StructRest::Rest(_) => {
self.ibox(INDENT_UNIT);
if !fields.is_empty() {
self.s.word(",");
self.s.space();
}
self.s.word("..");
self.print_expr(expr);
if let ast::StructRest::Base(ref expr) = *rest {
self.print_expr(expr);
}
self.end();
}
_ => {
if !fields.is_empty() {
self.s.word(",")
}
}
ast::StructRest::None if !fields.is_empty() => self.s.word(","),
_ => {}
}
self.s.word("}");
}
@ -1891,8 +1890,8 @@ impl<'a> State<'a> {
ast::ExprKind::Repeat(ref element, ref count) => {
self.print_expr_repeat(element, count, attrs);
}
ast::ExprKind::Struct(ref path, ref fields, ref wth) => {
self.print_expr_struct(path, &fields[..], wth, attrs);
ast::ExprKind::Struct(ref path, ref fields, ref rest) => {
self.print_expr_struct(path, &fields[..], rest, attrs);
}
ast::ExprKind::Tup(ref exprs) => {
self.print_expr_tup(&exprs[..], attrs);