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fix(WidgetOperation): avoid empty string for missing list widget container #42043

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fix(WidgetOperation): avoid empty string for missing list widget container #42043

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d82f18b
docs(helpers): document data loss from JSON round-trip in stringifyFn…
PedroHenrique0713 Jul 23, 2026
aac20ef
fix(formEval): replace second empty catch with descriptive comment
PedroHenrique0713 Jul 23, 2026
7ed6e75
fix(evalTree): guard against empty parsed updates array
PedroHenrique0713 Jul 23, 2026
1145874
fix(WidgetOperation): avoid empty string placeholder for missing list…
PedroHenrique0713 Jul 23, 2026
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2 changes: 1 addition & 1 deletion app/client/src/sagas/WidgetOperationUtils.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1876,7 +1876,7 @@ const updateListWidgetBindings = (
Object.keys(widgets).forEach((widgetId) => {
if (widgets[widgetId].parentId === listWidgetId) {
mainCanvasId = widgetId;
mainContainerId = widgets[widgetId].children?.[0] ?? "";
mainContainerId = widgets[widgetId].children?.[0] ?? undefined;
}
});

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4 changes: 3 additions & 1 deletion app/client/src/workers/Evaluation/formEval.ts
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Expand Up @@ -329,7 +329,9 @@ function evaluateFormConfigElements(
const evaluatedVal = eval(expression);

config[path].output = evaluatedVal;
} catch (e) {}
} catch (e) {
// form config evaluation error — skip this config entry
}
});
}

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5 changes: 3 additions & 2 deletions app/client/src/workers/Evaluation/handlers/evalTree.ts
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Expand Up @@ -307,8 +307,9 @@ export async function evalTree(
//for new tree send the whole thing, don't diff at all
updates = serialiseToBigInt([{ kind: "newTree", rhs: dataTree }]);
const parsedUpdates = JSON.parse(updates);

dataTreeEvaluator?.setPrevState(parsedUpdates[0].rhs);
if (parsedUpdates.length > 0) {
dataTreeEvaluator?.setPrevState(parsedUpdates[0].rhs);
}
} catch (e) {
updates = "[]";

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3 changes: 3 additions & 0 deletions app/client/src/workers/Evaluation/helpers.ts
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Expand Up @@ -111,6 +111,9 @@ export const stringifyFnsInObject = (
fnStrings.push(fnValue.toString());
}

// Note: JSON round-trip strips Dates, Sets, Maps, RegExps, and undefined values.
// Functions are preserved (collected before, re-injected after), but other
// non-JSON-safe types may be lost.
Comment on lines +114 to +116

@coderabbitai coderabbitai Bot Jul 23, 2026

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📐 Maintainability & Code Quality | 🟡 Minor | ⚡ Quick win

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail

printf 'Repository files matching helpers:\n'
fd -a 'helpers(\.test)?\.(ts|tsx)$' . | sed 's#^\./##' | rg 'app/client/src/workers/Evaluation/helpers' || true

printf '\nRelevant helper lines:\n'
sed -n '100,130p' app/client/src/workers/Evaluation/helpers.ts || true

printf '\nRelevant tests outline/lines:\n'
wc -l app/client/src/workers/Evaluation/helpers.test.ts
rg -n "JSON|function|Functions|helper|toJSON|call|()" app/client/src/workers/Evaluation/helpers.test.ts -C 2 || true
rg -n "collect|functions|JSON\.stringify|JSON\.parse|String(Replaces|Map)|inject|invoke" app/client/src/workers/Evaluation/helpers.ts -C 2 || true

printf '\nBehavioral JS probe for JSON stringify/parse semantics:\n'
node - <<'JS'
const cases = {
  date: new Date('2026-07-01T12:34:56.789Z'),
  undefInObj: {a: undefined, b: 1},
  undefInArr: [1, undefined, 2],
  map: new Map([['x', 1]]),
  set: new Set([1, 2]),
  regexp: /abc/,
  func: function named(){ return 42; },
  object: {a: undefined, b: [undefined]},
  sparse: [undefined],
};
for (const [name, value] of Object.entries(cases)) {
  const serialized = JSON.stringify(value);
  const rounds = JSON.parse(serialized);
  console.log(name + ': ' + serialized + ' -> ' + JSON.stringify(rounds) + ' [typeof: ' + typeof rounds + ']');
}
JS

Repository: appsmithorg/appsmith

Length of output: 10390

Correct the JSON round-trip behavior comment.

Date values become strings, object properties with undefined are omitted while array elements become null, and non-JSON-native types serialize as empty objects rather than being simply “stripped”. Also, fnStrings stores fnValue.toString(), so functions are reinserted as strings, not preserved as callable values.

Suggested wording 
-  // Note: JSON round-trip strips Dates, Sets, Maps, RegExps, and undefined values.
-  // Functions are preserved (collected before, re-injected after), but other
-  // non-JSON-safe types may be lost.
+  // Note: JSON round-trip converts Dates to strings and does not preserve
+  // undefined, Maps, Sets, RegExps, or other non-JSON-safe values.
+  // Functions are reinserted as their string representations.
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
// Note: JSON round-trip strips Dates, Sets, Maps, RegExps, and undefined values.
// Functions are preserved (collected before, re-injected after), but other
// non-JSON-safe types may be lost.
// Note: JSON round-trip converts Dates to strings and does not preserve
// undefined, Maps, Sets, RegExps, or other non-JSON-safe values.
// Functions are reinserted as their string representations.
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@app/client/src/workers/Evaluation/helpers.ts` around lines 114 - 116, Update
the JSON round-trip comment near fnStrings to accurately describe behavior:
Dates become strings, undefined object properties are omitted while array
elements become null, non-JSON-native types may serialize as empty objects, and
functions collected via fnValue.toString() are reinserted as strings rather than
callable values.

const output = JSON.parse(JSON.stringify(userObject));

for (const [index, parsedFnString] of fnStrings.entries()) {
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