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Simplify mergeEmitNode #59613

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Simplify mergeEmitNode #59613

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cf6e6ce
Simplify mergeEmitNode
jakebailey Aug 12, 2024
44f6caf
Fix lint
jakebailey Aug 12, 2024
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21 changes: 4 additions & 17 deletions src/compiler/factory/nodeFactory.ts
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Original file line number Diff line number Diff line change
@@ -1,9 +1,7 @@
import {
__String,
AccessorDeclaration,
addRange,
append,
appendIfUnique,
ArrayBindingElement,
ArrayBindingPattern,
ArrayLiteralExpression,
Expand Down Expand Up @@ -422,7 +420,6 @@ import {
TemplateMiddle,
TemplateSpan,
TemplateTail,
TextRange,
ThisExpression,
ThisTypeNode,
ThrowStatement,
Expand Down Expand Up @@ -7449,13 +7446,13 @@ function mergeEmitNode(sourceEmitNode: EmitNode, destEmitNode: EmitNode | undefi
// `leadingComments` are concatenated with any existing leading comments on the destination
if (leadingComments) {
// We use `.slice()` in case `destEmitNode.leadingComments` is pushed to later
destEmitNode.leadingComments = addRange(leadingComments.slice(), destEmitNode.leadingComments);
destEmitNode.leadingComments = leadingComments.slice();
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I worry this results in a different inconsistency now. Before, we would attempt to merge the emit information for the old node into anything set on the new node prior to calling setOriginalNode. Now we will conditionally overwrite some properties but not others.

const oldNode = ...;
addSyntheticLeadingComment(oldNode, SyntaxKind.SingleLineCommentTrivia, "foo");

const newNode = ...;
addSyntheticLeadingComment(oldNode, SyntaxKind.SingleLineCommentTrivia, "bar");
addSyntheticTrailingComment(oldNode, SyntaxKind.SingleLineCommentTrivia, "baz");

setOriginalNode(newNode, oldNode);

// before
getSyntheticLeadingComments(newNode).length; // 2 (foo and bar)
getSyntheticTrailingComments(newNode).length; // 1 (baz)

// after
getSyntheticLeadingComments(newNode).length; // 1 (foo)
getSyntheticTrailingComments(newNode).length; // 1 (baz)

After this change we end up with oldNode's leading comments but newNodes trailing comments, which seems more confusing.

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I certainly am not confident in this PR, but we do need something for #59332.

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I originally considered using appendIfUnique to avoid duplicating but also to concatenate. Would you think that's a good fix?

}

// `trailingComments` are concatenated with any existing trailing comments on the destination
if (trailingComments) {
// We use `.slice()` in case `destEmitNode.trailingComments` is pushed to later
destEmitNode.trailingComments = addRange(trailingComments.slice(), destEmitNode.trailingComments);
destEmitNode.trailingComments = trailingComments.slice();
}

// `commentRange` overwrites the destination
Expand All @@ -7470,7 +7467,7 @@ function mergeEmitNode(sourceEmitNode: EmitNode, destEmitNode: EmitNode | undefi

// `tokenSourceMapRanges` are merged with the destination
if (tokenSourceMapRanges) {
destEmitNode.tokenSourceMapRanges = mergeTokenSourceMapRanges(tokenSourceMapRanges, destEmitNode.tokenSourceMapRanges!);
destEmitNode.tokenSourceMapRanges = tokenSourceMapRanges.slice();
}

// `constantValue` overwrites the destination
Expand All @@ -7483,9 +7480,7 @@ function mergeEmitNode(sourceEmitNode: EmitNode, destEmitNode: EmitNode | undefi

// `helpers` are merged into the destination
if (helpers) {
for (const helper of helpers) {
destEmitNode.helpers = appendIfUnique(destEmitNode.helpers, helper);
}
destEmitNode.helpers = helpers.slice();
}

// `startsOnNewLine` overwrites the destination
Expand Down Expand Up @@ -7517,11 +7512,3 @@ function mergeEmitNode(sourceEmitNode: EmitNode, destEmitNode: EmitNode | undefi

return destEmitNode;
}

function mergeTokenSourceMapRanges(sourceRanges: (TextRange | undefined)[], destRanges: (TextRange | undefined)[]) {
if (!destRanges) destRanges = [];
for (const key in sourceRanges) {
destRanges[key] = sourceRanges[key];
}
return destRanges;
}
Comment on lines -7521 to -7527
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I read this function and it sort of scared me; what if the test has more elements than the source? Then I replaced it and nothing changed, so I kept going...

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sourceRanges and destRanges are holey arrays, so length doesn't actually matter. It probably should just be a Map<number, TextRange>, to be honest.