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NLL Diagnostic Review 3: Diagnostic mentions lack of initialization instead of incorrect mutability #55652

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davidtwco opened this issue Nov 3, 2018 · 1 comment · Fixed by #55657
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NLL Diagnostic Review 3: Diagnostic mentions lack of initialization instead of incorrect mutability #55652

davidtwco opened this issue Nov 3, 2018 · 1 comment · Fixed by #55657
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A-NLL Area: Non-lexical lifetimes (NLL) NLL-diagnostics Working towards the "diagnostic parity" goal P-medium Medium priority

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@pnkfelix's review comments:

ui/borrowck/reassignment_immutable_fields_overlapping.nll.stderr AST-borrowck complains about the local being immutable. NLL complains about lack of initialization. This is probably expected, but we should double-check.
@davidtwco davidtwco self-assigned this Nov 3, 2018
@davidtwco davidtwco added A-NLL Area: Non-lexical lifetimes (NLL) NLL-diagnostics Working towards the "diagnostic parity" goal labels Nov 3, 2018
@davidtwco davidtwco mentioned this issue Nov 3, 2018
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pnkfelix commented Nov 6, 2018 •
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triage: P-medium. (We should look into this, but even if its wrong, I'm not going to push to a backport its hypothetical bug fix.)

@pnkfelix pnkfelix added the P-medium Medium priority label Nov 6, 2018
bors added a commit that referenced this issue Nov 11, 2018
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Auto merge of #55657 - davidtwco:issue-55651, r=pnkfelix
5a2ca1a 
NLL Diagnostic Review 3: Unions not reinitialized after assignment into field

Fixes #55651, #55652.

This PR makes two changes:

First, it updates the dataflow builder to add an init for the place
containing a union if there is an assignment into the field of
that union.

Second, it stops a "use of uninitialized" error occuring when there is an
assignment into the field of an uninitialized union that was previously
initialized. Making this assignment would re-initialize the union, as
tested in `src/test/ui/borrowck/borrowck-union-move-assign.nll.stderr`.
The check for previous initialization ensures that we do not start
supporting partial initialization yet (cc #21232, #54499, #54986).

This PR also fixes #55652 which was marked as requiring investigation
as the changes in this PR add an error that was previously missing
(and mentioned in the review comments) and confirms that the error
that was present is correct and a result of earlier partial
initialization changes in NLL.

r? @pnkfelix (due to earlier work with partial initialization)
cc @nikomatsakis
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A-NLL Area: Non-lexical lifetimes (NLL) NLL-diagnostics Working towards the "diagnostic parity" goal P-medium Medium priority
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NLL Diagnostic Review 3: Unions not reinitialized after assignment into field davidtwco/rust
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