fix: deduplicate local variables for SSRv2 #5554
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| <template lwc:render-mode="light"> | ||
| <template for:each={relatedListData} for:item="list" if:true={relatedListData}> | ||
| <template for:each={list.recordIds} for:item="recordId"> | ||
| <template for:each={list.fields} for:item="field" for:index="index"> | ||
| <x-child key={field}> | ||
| <div>{field}</div> | ||
| </x-child> | ||
| </template> | ||
| </template> | ||
| </template> | ||
| </template> No newline at end of file |
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Before the change in this PR the output is this:
const __lwcGenerateShadowSlottedContent_xChild_0 = (list, __unused__, recordId, __unused__, field, index) => function __lwcGenerateShadowSlottedContent_xChild_0The double __unused__ led to a compilation error.
After this change it now appears as:
const __lwcGenerateShadowSlottedContent_xChild_0 = (list, __unused__, recordId, field, index) => function __lwcGenerateShadowSlottedContent_xChild_0There was a problem hiding this comment.
It's less likely to occur with user-provided variables, but deduping is also correct in that case because re-declared variables are shadowed; there's only one "version" of the variable in the scope where we call this function.
| const getLocalVars = () => localVarStack.flatMap((varsSet) => Array.from(varsSet)); | ||
| // Unique local variable names across block scopes, we don't care about block scope order | ||
| const getLocalVars = () => [ | ||
| ...new Set(localVarStack.flatMap((varsSet) => Array.from(varsSet))), | ||
| ]; |
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This is the main change, essentially we're just deduplicating the list.
Note that based on how we're using the array we don't really care about the order the variables appear in the block scopes.
| @@ -0,0 +1,2 @@ | |||
| <fixture-test> | |||
| </fixture-test> No newline at end of file | |||
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Is this supposed to be empty? 🤔
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Looks like I messed up the data in the array oops, I'll fix it.
wjhsf
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@nolanlawson would approve of the ratio of test files to lines of production code changed.
...-each-block/nested-no-index/modules/x/for-each-nested-no-index/for-each-nested-no-index.html
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| <template lwc:render-mode="light"> | ||
| <template for:each={relatedListData} for:item="list" if:true={relatedListData}> | ||
| <template for:each={list.recordIds} for:item="recordId"> | ||
| <template for:each={list.fields} for:item="field" for:index="index"> | ||
| <x-child key={field}> | ||
| <div>{field}</div> | ||
| </x-child> | ||
| </template> | ||
| </template> | ||
| </template> | ||
| </template> No newline at end of file |
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It's less likely to occur with user-provided variables, but deduping is also correct in that case because re-declared variables are shadowed; there's only one "version" of the variable in the scope where we call this function.
Details
The SSR v2 compiler keeps track of local variables via a stack.
When the local variables are retrieved we don't deduplicate them which can lead to errors, specifically:
LWC1001: Unexpected compilation error: Duplicate argument name "unused":
This PR introduces a fix by deduping the variables before use.
Does this pull request introduce a breaking change?
Does this pull request introduce an observable change?
GUS work item
W-19971203