Repository: facebook/react
Pull request: [compiler] clarify text for setState-in-effect error

---
[//]: # (BEGIN SAPLING FOOTER)
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* #33993
* __->__ #33991
* #33984

Changed files:
filename: compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoSetStateInEffects.ts
patch: @@ -97,16 +97,21 @@ export function validateNoSetStateInEffects(
                 errors.pushDiagnostic(
                   CompilerDiagnostic.create({
                     category:
-                      'Calling setState within an effect can trigger cascading renders',
+                      'Calling setState synchronously within an effect can trigger cascading renders',
                     description:
-                      'Calling setState directly within a useEffect causes cascading renders that can hurt performance, and is not recommended. Consider alternatives to useEffect. (https://react.dev/learn/you-might-not-need-an-effect)',
+                      'Effects are intended to synchronize state between React and external systems such as manually updating the DOM, state management libraries, or other platform APIs. ' +
+                      'In general, the body of an effect should do one or both of the following:\n' +
+                      '* Update external systems with the latest state from React.\n' +
+                      '* Subscribe for updates from some external system, calling setState in a callback function when external state changes.\n\n' +
+                      'Calling setState synchronously within an effect body causes cascading renders that can hurt performance, and is not recommended. ' +
+                      '(https://react.dev/learn/you-might-not-need-an-effect)',
                     severity: ErrorSeverity.InvalidReact,
                     suggestions: null,
                   }).withDetail({
                     kind: 'error',
                     loc: setState.loc,
                     message:
-                      'Avoid calling setState() in the top-level of an effect',
+                      'Avoid calling setState() directly within an effect',
                   }),
                 );
               }

filename: compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/invalid-setState-in-useEffect-transitive.expect.md
patch: @@ -65,7 +65,7 @@ function _temp(s) {
 ## Logs
 
 ```
-{"kind":"CompileError","detail":{"options":{"category":"Calling setState within an effect can trigger cascading renders","description":"Calling setState directly within a useEffect causes cascading renders that can hurt performance, and is not recommended. Consider alternatives to useEffect. (https://react.dev/learn/you-might-not-need-an-effect)","severity":"InvalidReact","suggestions":null,"details":[{"kind":"error","loc":{"start":{"line":13,"column":4,"index":265},"end":{"line":13,"column":5,"index":266},"filename":"invalid-setState-in-useEffect-transitive.ts","identifierName":"g"},"message":"Avoid calling setState() in the top-level of an effect"}]}},"fnLoc":null}
+{"kind":"CompileError","detail":{"options":{"category":"Calling setState synchronously within an effect can trigger cascading renders","description":"Effects are intended to synchronize state between React and external systems such as manually updating the DOM, state management libraries, or other platform APIs. In general, the body of an effect should do one or both of the following:\n* Update external systems with the latest state from React.\n* Subscribe for updates from some external system, calling setState in a callback function when external state changes.\n\nCalling setState synchronously within an effect body causes cascading renders that can hurt performance, and is not recommended. (https://react.dev/learn/you-might-not-need-an-effect)","severity":"InvalidReact","suggestions":null,"details":[{"kind":"error","loc":{"start":{"line":13,"column":4,"index":265},"end":{"line":13,"column":5,"index":266},"filename":"invalid-setState-in-useEffect-transitive.ts","identifierName":"g"},"message":"Avoid calling setState() directly within an effect"}]}},"fnLoc":null}
 {"kind":"CompileSuccess","fnLoc":{"start":{"line":4,"column":0,"index":92},"end":{"line":16,"column":1,"index":293},"filename":"invalid-setState-in-useEffect-transitive.ts"},"fnName":"Component","memoSlots":2,"memoBlocks":2,"memoValues":2,"prunedMemoBlocks":0,"prunedMemoValues":0}
 ```
       

filename: compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/invalid-setState-in-useEffect.expect.md
patch: @@ -45,7 +45,7 @@ function _temp(s) {
 ## Logs
 
 ```
-{"kind":"CompileError","detail":{"options":{"category":"Calling setState within an effect can trigger cascading renders","description":"Calling setState directly within a useEffect causes cascading renders that can hurt performance, and is not recommended. Consider alternatives to useEffect. (https://react.dev/learn/you-might-not-need-an-effect)","severity":"InvalidReact","suggestions":null,"details":[{"kind":"error","loc":{"start":{"line":7,"column":4,"index":180},"end":{"line":7,"column":12,"index":188},"filename":"invalid-setState-in-useEffect.ts","identifierName":"setState"},"message":"Avoid calling setState() in the top-level of an effect"}]}},"fnLoc":null}
+{"kind":"CompileError","detail":{"options":{"category":"Calling setState synchronously within an effect can trigger cascading renders","description":"Effects are intended to synchronize state between React and external systems such as manually updating the DOM, state management libraries, or other platform APIs. In general, the body of an effect should do one or both of the following:\n* Update external systems with the latest state from React.\n* Subscribe for updates from some external system, calling setState in a callback function when external state changes.\n\nCalling setState synchronously within an effect body causes cascading renders that can hurt performance, and is not recommended. (https://react.dev/learn/you-might-not-need-an-effect)","severity":"InvalidReact","suggestions":null,"details":[{"kind":"error","loc":{"start":{"line":7,"column":4,"index":180},"end":{"line":7,"column":12,"index":188},"filename":"invalid-setState-in-useEffect.ts","identifierName":"setState"},"message":"Avoid calling setState() directly within an effect"}]}},"fnLoc":null}
 {"kind":"CompileSuccess","fnLoc":{"start":{"line":4,"column":0,"index":92},"end":{"line":10,"column":1,"index":225},"filename":"invalid-setState-in-useEffect.ts"},"fnName":"Component","memoSlots":1,"memoBlocks":1,"memoValues":1,"prunedMemoBlocks":0,"prunedMemoValues":0}
 ```