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fix #2080 fix #2085 fix #2098 fix #2099: var bug
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‎CHANGELOG.md‎

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## Unreleased
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* Fix a tree shaking regression regarding `var` declarations ([#2080](https://github.com/evanw/esbuild/issues/2080), [#2085](https://github.com/evanw/esbuild/pull/2085), [#2098](https://github.com/evanw/esbuild/issues/2098), [#2099](https://github.com/evanw/esbuild/issues/2099))
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Version 0.14.8 of esbuild enabled removal of duplicate function declarations when minification is enabled (see [#610](https://github.com/evanw/esbuild/issues/610)):
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```js
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// Original code
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function x() { return 1 }
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console.log(x())
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function x() { return 2 }
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// Output (with --minify-syntax)
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console.log(x());
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function x() {
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return 2;
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}
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```
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This transformation is safe because function declarations are "hoisted" in JavaScript, which means they are all done first before any other code is evaluted. This means the last function declaration will overwrite all previous function declarations with the same name.
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However, this introduced an unintentional regression for `var` declarations in which all but the last declaration was dropped if tree-shaking was enabled. This only happens for top-level `var` declarations that re-declare the same variable multiple times. This regression has now been fixed:
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```js
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// Original code
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var x = 1
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console.log(x)
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var x = 2
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// Old output (with --tree-shaking=true)
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console.log(x);
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var x = 2;
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// New output (with --tree-shaking=true)
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var x = 1;
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console.log(x);
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var x = 2;
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```
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This case now has test coverage.
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* Add support for parsing "instantiation expressions" from TypeScript 4.7 ([#2038](https://github.com/evanw/esbuild/pull/2038))
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The upcoming version of TypeScript now lets you specify `<...>` type parameters on a JavaScript identifier without using a call expression:

‎internal/bundler/bundler_dce_test.go‎

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@@ -3016,3 +3016,87 @@ func TestCrossModuleConstantFolding(t *testing.T) {
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},
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})
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}
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func TestMultipleDeclarationTreeShaking(t *testing.T) {
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dce_suite.expectBundled(t, bundled{
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files: map[string]string{
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"/var2.js": `
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var x = 1
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console.log(x)
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var x = 2
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`,
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"/var3.js": `
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var x = 1
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console.log(x)
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var x = 2
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console.log(x)
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var x = 3
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`,
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"/function2.js": `
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function x() { return 1 }
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console.log(x())
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function x() { return 2 }
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`,
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"/function3.js": `
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function x() { return 1 }
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console.log(x())
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function x() { return 2 }
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console.log(x())
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function x() { return 3 }
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`,
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},
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entryPaths: []string{
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"/var2.js",
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"/var3.js",
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"/function2.js",
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"/function3.js",
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},
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options: config.Options{
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Mode: config.ModeBundle,
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AbsOutputDir: "/out",
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MinifySyntax: false,
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},
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})
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}
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func TestMultipleDeclarationTreeShakingMinifySyntax(t *testing.T) {
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dce_suite.expectBundled(t, bundled{
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files: map[string]string{
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"/var2.js": `
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var x = 1
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console.log(x)
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var x = 2
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`,
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"/var3.js": `
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var x = 1
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console.log(x)
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var x = 2
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console.log(x)
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var x = 3
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`,
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"/function2.js": `
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function x() { return 1 }
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console.log(x())
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function x() { return 2 }
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`,
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"/function3.js": `
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function x() { return 1 }
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console.log(x())
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function x() { return 2 }
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console.log(x())
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function x() { return 3 }
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`,
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},
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entryPaths: []string{
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"/var2.js",
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"/var3.js",
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"/function2.js",
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"/function3.js",
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},
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options: config.Options{
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Mode: config.ModeBundle,
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AbsOutputDir: "/out",
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MinifySyntax: true,
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},
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})
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}

‎internal/bundler/snapshots/snapshots_dce.txt‎

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// entry.js
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console.log("unused import");
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================================================================================
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TestMultipleDeclarationTreeShaking
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---------- /out/var2.js ----------
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// var2.js
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var x = 1;
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console.log(x);
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var x = 2;
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---------- /out/var3.js ----------
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// var3.js
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var x = 1;
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console.log(x);
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var x = 2;
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console.log(x);
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var x = 3;
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---------- /out/function2.js ----------
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// function2.js
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function x() {
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return 1;
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}
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console.log(x());
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function x() {
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return 2;
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}
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---------- /out/function3.js ----------
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// function3.js
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function x() {
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return 1;
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}
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console.log(x());
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function x() {
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return 2;
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}
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console.log(x());
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function x() {
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return 3;
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}
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================================================================================
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TestMultipleDeclarationTreeShakingMinifySyntax
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---------- /out/var2.js ----------
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// var2.js
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var x = 1;
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console.log(x);
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var x = 2;
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---------- /out/var3.js ----------
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// var3.js
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var x = 1;
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console.log(x);
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var x = 2;
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console.log(x);
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var x = 3;
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---------- /out/function2.js ----------
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// function2.js
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console.log(x());
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function x() {
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return 2;
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}
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---------- /out/function3.js ----------
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// function3.js
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console.log(x());
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console.log(x());
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function x() {
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return 3;
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}
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================================================================================
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TestPackageJsonSideEffectsArrayGlob
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---------- /out.js ----------

‎internal/js_parser/js_parser.go‎

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for partIndex, part := range parts {
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for _, declared := range part.DeclaredSymbols {
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if declared.IsTopLevel {
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p.topLevelSymbolToParts[declared.Ref] = append(
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p.topLevelSymbolToParts[declared.Ref], uint32(partIndex))
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// If this symbol was merged, use the symbol at the end of the
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// linked list in the map. This is the case for multiple "var"
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// declarations with the same name, for example.
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ref := declared.Ref
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for p.symbols[ref.InnerIndex].Link != js_ast.InvalidRef {
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ref = p.symbols[ref.InnerIndex].Link
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}
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p.topLevelSymbolToParts[ref] = append(
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p.topLevelSymbolToParts[ref], uint32(partIndex))
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}
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}
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}

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