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Struct Update/ Functional record update syntax error #32

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arora-aman opened this issue Dec 4, 2020 · 1 comment · Fixed by rust-lang/rust#81291
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Struct Update/ Functional record update syntax error #32

arora-aman opened this issue Dec 4, 2020 · 1 comment · Fixed by rust-lang/rust#81291
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arora-aman commented Dec 4, 2020 •
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struct X {
    a : String,
    b : String,
    c : String,
}

impl X {
    fn from_other_X(o: Self) -> Self {
        let c = || {
            X { a: "".into(), ..o }
        };
        c()
    }
}

The closure captures o.b, and o.c. But in MIR we expect to see *o which causes issues
@arora-aman arora-aman added the bug Something isn't working label Dec 4, 2020
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The projections are generated here: https://github.com/rust-lang/rust/blob/40dfe1eddd35d65348c40abe12dc5c659d068e2c/compiler/rustc_typeck/src/expr_use_visitor.rs#L419-L426

@roxelo roxelo self-assigned this Jan 5, 2021
@arora-aman arora-aman assigned null-sleep and unassigned roxelo Jan 19, 2021
@null-sleep null-sleep mentioned this issue Jan 23, 2021
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henryboisdequin added a commit to henryboisdequin/rust that referenced this issue Jan 29, 2021
@henryboisdequin
Rollup merge of rust-lang#81291 - sexxi-goose:fix-struct-update-funct…
1256217 
…ional-record-update-syntax-error, r=nikomatsakis

Support FRU pattern with `[feature(capture_disjoint_fields)]`

In case of a functional record update syntax for creating a structure, `ExprUseVisitor` to only detect the precise use of some of the field in the `..x` part of the syntax. However, when we start building MIR, we
1. First, build the place for `x`
2. and then, add precise field projections so that only some parts of `x` end up getting read.

When `capture_disjoint_fields` is enabled, and FRU is used within a closure `x` won't be completely captured, and therefore the first step will fail. This PR updates `mir_build` to create a place builder in the first step and then create place from the builder only after applying the field projection.

Closes rust-lang/project-rfc-2229#32
r? `@nikomatsakis`
@nikomatsakis nikomatsakis added this to the Feature complete milestone Feb 17, 2021
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Support FRU pattern with [feature(capture_disjoint_fields)] sexxi-goose/rust
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