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https://github.com/facebook/react.git
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Object and array destructuring support in declaration/assignment
Implements support for array and object de-structuring in variable declarations and assignment expressions. Note that the code currently makes the overly optimistic assumption that the RHS is an array or object that can be safely indexed into. The correct representation would instead treat the RHS as possibly iterable, but we need to consider the appropriate representation. I think it's worth landing a first optimistic pass and we can iterate forward, this helps make it more clear what the ideal representation would have to be and should make a bunch of examples work. It also allows us to experiment with representations of, and handling for, scope dependencies that involve computed property access.
This commit is contained in:
Joe Savona
@@ -623,10 +623,6 @@ function lowerStatement(
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nodeKind === "let" ? InstructionKind.Let : InstructionKind.Const;
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for (const declaration of stmt.get("declarations")) {
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const id = declaration.get("id");
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invariant(
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id.isIdentifier(),
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"Support non-identifier variable declarations"
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);
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const init = declaration.get("init");
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let value: InstructionValue;
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if (init.hasNode()) {
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@@ -942,45 +938,13 @@ function lowerExpression(
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if (operator === "=") {
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const left = expr.get("left");
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const leftNode = left.node;
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switch (leftNode.type) {
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case "Identifier": {
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const lvalue = left as NodePath<t.Identifier>;
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return lowerAssignment(
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builder,
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leftNode.loc ?? GeneratedSource,
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InstructionKind.Reassign,
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lvalue,
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lowerExpression(builder, expr.get("right"))
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);
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}
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case "MemberExpression": {
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const leftExpr = left as NodePath<t.MemberExpression>;
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const property = leftExpr.get("property");
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invariant(
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property.isIdentifier(),
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"Assignment expression to dynamic properties is not yet supported"
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);
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const right = lowerExpressionToPlace(builder, expr.get("right"));
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const object = lowerExpressionToPlace(
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builder,
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leftExpr.get("object")
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);
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return {
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kind: "PropertyStore",
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object,
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property: property.node.name,
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value: right,
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loc: leftNode.loc ?? GeneratedSource,
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};
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}
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default: {
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todoInvariant(
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false,
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"Support lvalues other than identifier and member expression"
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);
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}
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}
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return lowerAssignment(
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builder,
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left.node.loc ?? GeneratedSource,
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InstructionKind.Reassign,
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left,
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lowerExpression(builder, expr.get("right"))
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);
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}
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const operators: { [key: string]: t.BinaryExpression["operator"] } = {
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@@ -1399,15 +1363,131 @@ function lowerAssignment(
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builder: HIRBuilder,
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loc: SourceLocation,
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kind: InstructionKind,
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lvalue: NodePath<t.Identifier>,
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lvaluePath: NodePath<t.LVal>,
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value: InstructionValue
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): InstructionValue {
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const id = lowerIdentifier(builder, lvalue);
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builder.push({
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id: makeInstructionId(0),
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lvalue: { place: id, kind },
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value,
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loc,
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});
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return id;
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const lvalueNode = lvaluePath.node;
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switch (lvalueNode.type) {
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case "Identifier": {
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const lvalue = lvaluePath as NodePath<t.Identifier>;
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const place = lowerIdentifier(builder, lvalue);
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builder.push({
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id: makeInstructionId(0),
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lvalue: { place: { ...place }, kind },
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value,
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loc,
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});
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return place;
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}
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case "MemberExpression": {
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const leftExpr = lvaluePath as NodePath<t.MemberExpression>;
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const property = leftExpr.get("property");
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invariant(
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property.isIdentifier(),
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"Assignment expression to dynamic properties is not yet supported"
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);
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const object = lowerExpressionToPlace(builder, leftExpr.get("object"));
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let valuePlace: Place;
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if (value.kind === "Identifier") {
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valuePlace = value;
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} else {
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valuePlace = buildTemporaryPlace(builder, loc);
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builder.push({
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id: makeInstructionId(0),
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lvalue: { place: { ...valuePlace }, kind: InstructionKind.Const },
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value,
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loc,
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});
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}
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return {
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kind: "PropertyStore",
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object,
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property: property.node.name,
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value: valuePlace,
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loc,
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};
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}
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case "ArrayPattern": {
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const lvalue = lvaluePath as NodePath<t.ArrayPattern>;
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const arrayPlace = buildTemporaryPlace(builder, loc);
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builder.push({
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id: makeInstructionId(0),
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lvalue: { place: { ...arrayPlace }, kind: InstructionKind.Const },
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value,
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loc,
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});
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const elements = lvalue.get("elements");
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for (let i = 0; i < elements.length; i++) {
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const element = elements[i];
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if (!element.hasNode()) {
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continue;
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}
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todoInvariant(
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element.node.type !== "RestElement",
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"Rest elements are not supported yet"
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);
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const property = buildTemporaryPlace(
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builder,
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element.node.loc ?? GeneratedSource
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);
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builder.push({
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id: makeInstructionId(0),
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lvalue: { place: { ...property }, kind: InstructionKind.Const },
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value: {
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kind: "Primitive",
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value: i,
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loc: element.node.loc ?? GeneratedSource,
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},
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loc: element.node.loc ?? GeneratedSource,
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});
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const value: InstructionValue = {
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kind: "IndexLoad",
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loc,
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object: { ...arrayPlace },
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property,
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};
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lowerAssignment(builder, loc, kind, element, value);
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}
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return arrayPlace;
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}
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case "ObjectPattern": {
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const lvalue = lvaluePath as NodePath<t.ObjectPattern>;
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const objectPlace = buildTemporaryPlace(builder, loc);
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builder.push({
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id: makeInstructionId(0),
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lvalue: { place: { ...objectPlace }, kind },
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value,
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loc,
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});
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const properties = lvalue.get("properties");
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for (let i = 0; i < properties.length; i++) {
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const property = properties[i];
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invariant(
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property.isObjectProperty(),
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"Rest elements are not supported yet"
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);
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const key = property.get("key");
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invariant(
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key.isIdentifier(),
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"TODO: support non-identifier object property keys"
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);
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const element = property.get("value");
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invariant(
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element.isLVal(),
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"Expected object property value to be an lvalue"
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);
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const value: InstructionValue = {
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kind: "PropertyLoad",
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loc,
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object: { ...objectPlace },
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property: key.node.name,
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};
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lowerAssignment(builder, loc, kind, element, value);
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}
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return objectPlace;
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}
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default: {
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todo("Support other lvalue types beyond identifier");
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}
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}
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}
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@@ -0,0 +1,40 @@
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## Input
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```javascript
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function foo(a, b, c) {
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let d, g, n, o;
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[
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d,
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[
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{
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e: { f: g },
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},
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],
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] = a;
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({
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l: {
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m: [[n]],
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},
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o,
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} = b);
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}
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```
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## Code
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```javascript
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function foo(a, b, c) {
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const d = undefined;
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const g = undefined;
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const n = undefined;
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const o = undefined;
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const d$0 = a[0];
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const g$1 = a[1][0].e.f;
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const n$2 = b.l.m[0][0];
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const o$3 = b.o;
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}
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```
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@@ -0,0 +1,17 @@
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function foo(a, b, c) {
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let d, g, n, o;
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[
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d,
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[
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{
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e: { f: g },
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},
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],
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] = a;
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({
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l: {
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m: [[n]],
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},
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o,
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} = b);
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}
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@@ -0,0 +1,35 @@
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## Input
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```javascript
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function foo(a, b, c) {
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const [
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d,
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[
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{
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e: { f },
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},
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],
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] = a;
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const {
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l: {
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m: [[n]],
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},
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o,
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} = b;
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}
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```
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## Code
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```javascript
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function foo(a, b, c) {
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const d = a[0];
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const f = a[1][0].e.f;
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const n = b.l.m[0][0];
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const o = b.o;
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}
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```
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@@ -0,0 +1,16 @@
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function foo(a, b, c) {
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const [
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d,
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[
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{
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e: { f },
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},
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],
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] = a;
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const {
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l: {
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m: [[n]],
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},
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o,
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} = b;
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}
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