[compiler] Fix for destructuring with mixed declaration/reassignment #35144
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josephsavona
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Nov 14, 2025
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| const isDeclared = cx.hasDeclared(place.identifier); | ||
| hasReassign ||= isDeclared; | ||
| hasDeclaration ||= !isDeclared; | ||
| } | ||
| if (hasReassign && hasDeclaration) { | ||
| CompilerError.invariant(false, { | ||
| reason: | ||
| 'Encountered a destructuring operation where some identifiers are already declared (reassignments) but others are not (declarations)', | ||
| description: null, | ||
| details: [ | ||
| { | ||
| kind: 'error', | ||
| loc: instr.loc, | ||
| message: null, | ||
| }, | ||
| ], | ||
| suggestions: null, | ||
| }); | ||
| } else if (hasReassign) { | ||
| kind = InstructionKind.Reassign; |
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the logic for hasDeclared() here doesn't account for all local variables, so it was incorrectly reporting that the fixed destructuring had mixed reassignment and declarations
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Oh I see -- we add to declarations only when we see scope declarations, but this case has a local (with-scope) reassignment
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--- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/35145). * #35144 * __->__ #35145
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--- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/35145). * facebook#35144 * __->__ facebook#35145
mofeiZ
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| if (reassigned.size === 0 || !hasDeclaration) { | ||
| if (!hasDeclaration) { | ||
| // all reassignments | ||
| destructure.lvalue.kind = InstructionKind.Reassign; |
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hmm just curious -- was this line necessary? We previously didn't need to always either overwrite or construct a new Destructure instruction. Mainly wondering if there was more than one bugfix here
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Yes, because before these cases would have fallen through to the code below which replaced the instruction with a Reassign kind.
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| if (view === "week") { | ||
| let lastDay; | ||
|
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| [firstDay, lastDay] = getConfig(weekendDays); |
mofeiZ
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Nov 17, 2025
Destructing statements that start off as declarations can end up becoming reassignments if the variable is a scope declaration, so we have existing logic to handle cases where some parts of a destructure need to be converted into new locals, with a reassignment to the hoisted scope variable afterwards. However, there is an edge case where all of the values are reassigned, in which case we don't need to rewrite and can just set the instruction kind to reassign.
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…35144) Destructing statements that start off as declarations can end up becoming reassignments if the variable is a scope declaration, so we have existing logic to handle cases where some parts of a destructure need to be converted into new locals, with a reassignment to the hoisted scope variable afterwards. However, there is an edge case where all of the values are reassigned, in which case we don't need to rewrite and can just set the instruction kind to reassign. --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/35144). * #35148 * #35147 * #35146 * __->__ #35144 DiffTrain build for [b315a0f](b315a0f)
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…35144) Destructing statements that start off as declarations can end up becoming reassignments if the variable is a scope declaration, so we have existing logic to handle cases where some parts of a destructure need to be converted into new locals, with a reassignment to the hoisted scope variable afterwards. However, there is an edge case where all of the values are reassigned, in which case we don't need to rewrite and can just set the instruction kind to reassign. --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/35144). * #35148 * #35147 * #35146 * __->__ #35144 DiffTrain build for [b315a0f](b315a0f)
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Destructing statements that start off as declarations can end up becoming reassignments if the variable is a scope declaration, so we have existing logic to handle cases where some parts of a destructure need to be converted into new locals, with a reassignment to the hoisted scope variable afterwards. However, there is an edge case where all of the values are reassigned, in which case we don't need to rewrite and can just set the instruction kind to reassign.
Stack created with Sapling. Best reviewed with ReviewStack.