Failed to parse JSON for tool call 'replace_string_in_file': SyntaxError

[gnl42]

Asked "Claude Sonnet 4.6" to refactor the code:

(there is no C:\snapshot\copilot-intellij\lib\src\openai\ folder, or even C:\snapshot\, folder

eclipse.buildId=4.39.0.20260305-0817
java.version=21.0.10
java.vendor=Eclipse Adoptium
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=en_CA
Framework arguments:  -product org.eclipse.epp.package.rcp.product
Command-line arguments:  -os win32 -ws win32 -arch x86_64 -product org.eclipse.epp.package.rcp.product -data file:/E:/workspaces/JiraConnector/

Copilot: 0.15.0

!ENTRY org.eclipse.lsp4e 4 0 2026-03-17 00:29:03.334
!MESSAGE [LS:GitHub Copilot Language Server][Error]	[toolCallingLoop] Fetch failed: {
  type: 'failed',
  reason: "Error on conversation request: Failed to parse JSON for tool call 'replace_string_in_file': SyntaxError: Expected ',' or '}' after property value in JSON at position 235 (line 1 column 236)\n" +
    '    at JSON.parse (<anonymous>)\n' +
    '    at parseCallArguments (C:\\snapshot\\copilot-intellij\\lib\\src\\openai\\stream.ts:805:21)\n' +
    '    at extractToolCalls (C:\\snapshot\\copilot-intellij\\lib\\src\\openai\\stream.ts:8... Read more from logs.',
  requestId: '4c2a9f24-1263-4f82-8100-e18f50ba34ae'
}

!ENTRY org.eclipse.lsp4e 4 0 2026-03-17 00:29:03.334
!MESSAGE [LS:GitHub Copilot Language Server][Error]	[chat] Error on conversation request: Error: Failed to parse JSON for tool call 'replace_string_in_file': SyntaxError: Expected ',' or '}' after property value in JSON at position 235 (line 1 column 236)
    at JSON.parse (<anonymous>)
    at parseCallArguments (C:\snapshot\copilot-intellij\lib\src\openai\stream.ts:805:21)
    at extractToolCalls (C:\snapshot\copilot-intellij\lib\src\openai\stream.ts:821:26)
    at convertToAPIJsonData (C:\snapshot\copilot-intellij\lib\src\openai\stream.ts:751:23)
    at prepareChatCompletionForReturn (C:\snapshot\copilot-intellij\lib\src\conversation\openai\stream.ts:28:35)
    at selector (C:\snapshot\copilot-intellij\lib\src\conversation\endpoint\ChatCompletionsEndpointStrategy.ts:202:13)
    at asyncIterableMap (C:\snapshot\copilot-intellij\lib\src\common\iterableHelpers.ts:6:15)
    at process.item (node:internal/process/task_queues:105:5)
    at chatCompletion (C:\snapshot\copilot-intellij\lib\src\common\iterableHelpers.ts:25:22)
    at ea.processSuccessfulResponse (C:\snapshot\copilot-intellij\lib\src\conversation\chatMLFetcher.ts:392:26). Input: '{"explanation": "Update JsonWeakParser to throw JsonProcessingException instead of JSONException", "filePath": "E:\\git\\JiraConnector\\jrjc-core\\src\\main\\java\\me\\glindholm\\jira\\rest\\client\\internal\\json\\JsonWeakParser.java"'
    at parseCallArguments (C:\snapshot\copilot-intellij\lib\src\openai\stream.ts:810:15)
    at extractToolCalls (C:\snapshot\copilot-intellij\lib\src\openai\stream.ts:821:26)
    at convertToAPIJsonData (C:\snapshot\copilot-intellij\lib\src\openai\stream.ts:751:23)
    at prepareChatCompletionForReturn (C:\snapshot\copilot-intellij\lib\src\conversation\openai\stream.ts:28:35)
    at selector (C:\snapshot\copilot-intellij\lib\src\conversation\endpoint\ChatCompletionsEndpointStrategy.ts:202:13)
    at asyncIterableMap (C:\snapshot\copilot-intellij\lib\src\common\iterableHelpers.ts:6:15)
    at process.item (node:internal/process/task_queues:105:5)
    at chatCompletion (C:\snapshot\copilot-intellij\lib\src\common\iterableHelpers.ts:25:22)
    at ea.processSuccessfulResponse (C:\snapshot\copilot-intellij\lib\src\conversation\chatMLFetcher.ts:392:26)
    at ea.fetch (C:\snapshot\copilot-intellij\lib\src\conversation\chatMLFetcher.ts:349:28)

!ENTRY com.microsoft.copilot.eclipse 4 0 2026-03-17 00:29:04.041
!MESSAGE [Error] Failed to persist conversation progress: 4d1ae4b7-3b64-47a2-8e2b-5da1845cf3c5
!STACK 0
java.io.IOException: Failed to load conversation index document
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.updateConversationIndex(ConversationPersistenceService.java:146)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.saveConversation(ConversationPersistenceService.java:95)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceManager.persistAndCacheConversation(ConversationPersistenceManager.java:398)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceManager.lambda$4(ConversationPersistenceManager.java:224)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188)
Caused by: org.xml.sax.SAXParseException; lineNumber: 11; columnNumber: 201; XML document structures must start and end within the same entity.
	at java.xml/com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:262)
	at java.xml/com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:342)
	at java.xml/javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:122)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.loadIndexDocument(ConversationPersistenceService.java:242)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.loadOrCreateIndexDocument(ConversationPersistenceService.java:230)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.updateConversationIndex(ConversationPersistenceService.java:142)
	... 10 more

!ENTRY com.microsoft.copilot.eclipse 4 0 2026-03-17 00:29:04.077
!MESSAGE [Error] Failed to update todo list for conversation: 4d1ae4b7-3b64-47a2-8e2b-5da1845cf3c5
!STACK 0
java.io.IOException: Failed to load conversation index document
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.updateConversationIndex(ConversationPersistenceService.java:146)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.saveConversation(ConversationPersistenceService.java:95)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceManager.persistAndCacheConversation(ConversationPersistenceManager.java:398)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceManager.lambda$10(ConversationPersistenceManager.java:457)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188)
Caused by: org.xml.sax.SAXParseException; lineNumber: 11; columnNumber: 201; XML document structures must start and end within the same entity.
	at java.xml/com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:262)
	at java.xml/com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:342)
	at java.xml/javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:122)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.loadIndexDocument(ConversationPersistenceService.java:242)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.loadOrCreateIndexDocument(ConversationPersistenceService.java:230)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.updateConversationIndex(ConversationPersistenceService.java:142)
	... 10 more

!ENTRY com.microsoft.copilot.eclipse 4 0 2026-03-17 00:29:04.079
!MESSAGE [Error] Failed to persist model info for conversation: 4d1ae4b7-3b64-47a2-8e2b-5da1845cf3c5
!STACK 0
java.io.IOException: Failed to load conversation index document
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.updateConversationIndex(ConversationPersistenceService.java:146)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.saveConversation(ConversationPersistenceService.java:95)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceManager.persistAndCacheConversation(ConversationPersistenceManager.java:398)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceManager.lambda$12(ConversationPersistenceManager.java:526)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188)
Caused by: org.xml.sax.SAXParseException; lineNumber: 11; columnNumber: 201; XML document structures must start and end within the same entity.
	at java.xml/com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:262)
	at java.xml/com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:342)
	at java.xml/javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:122)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.loadIndexDocument(ConversationPersistenceService.java:242)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.loadOrCreateIndexDocument(ConversationPersistenceService.java:230)
	at com.microsoft.copilot.eclipse.core.persistence.ConversationPersistenceService.updateConversationIndex(ConversationPersistenceService.java:142)
	... 10 more

[jdneo]

This could probably the CAPI side issue, which is under fixing as far as I know.

cc @iloveeclipse

[iloveeclipse]

This could probably the CAPI side issue, which is under fixing as far as I know.

Thanks.

1. Could you link to the ticket, if there is one? If there is no ticket created for CAPI, should one be created? We are interested in the timeline for the possible solution.
2. Assuming this is a bug in CAPI and there will be a fix, would it then require a new Copilot Eclipse plugin build, or is this fully server-side "github infra" fix, which would not require new plugin build?

[jdneo]

That is an internal ticket which I do not have access either. :(

I guess it should be fully server side issue.

[jdneo]

upstream issue for tracking: https://github.com/microsoft/copilot-language-server-internal/issues/313

[iloveeclipse]

Got one user report, when selecting Claude Sonnet 4.6 in agent mode, a complex prompt leads to the following error message:

Sorry, an error occurred while generating a response. Details: unhandled status from server: 400 {"error":{"message":"This model does not support assistant message prefill. The conversation must end with a user message.","code":"invalid_request_body"}} Request ID: 058d3120-1328-43f7-9885-24fdc49cc20f

Not sure if this is same or not (at least seem to be same model issue)? Used Copilot was likely 0.14 version.

[jdneo]

Is this issue stable reproducible?

[gnl42]

Never reproducible.
Happened again:

Copilot 0.16.0

eclipse.buildId=4.39.0.20260305-0817
java.version=21.0.10
java.vendor=Ubuntu
BootLoader constants: OS=linux, ARCH=x86_64, WS=gtk, NL=en_CA
Framework arguments:  -product org.eclipse.epp.package.committers.product
Command-line arguments:  -os linux -ws gtk -arch x86_64 -product org.eclipse.epp.package.committers.product -data file:/home/xxx/workspaces/mylyn-main/ws/

[LS:GitHub Copilot Language Server][Error]	[toolCallingLoop] Fetch failed: {
  type: 'failed',
  reason: "Error on conversation request: Failed to parse JSON for tool call 'replace_string_in_file': SyntaxError: Expected ',' or '}' after property value in JSON at position 188 (line 1 column 189)\n" +
    '    at JSON.parse (<anonymous>)\n' +
    '    at parseCallArguments (/snapshot/copilot-intellij/lib/src/openai/stream.ts:836:21)\n' +
    '    at extractToolCalls (/snapshot/copilot-intellij/lib/src/openai/stream.ts:852:2... Read more from logs.',
  requestId: '5bc57599-9b52-4520-957d-baa4d37a76e4'
}

[LS:GitHub Copilot Language Server][Error]	[chat] Error on conversation request: Error: Failed to parse JSON for tool call 'replace_string_in_file': SyntaxError: Expected ',' or '}' after property value in JSON at position 188 (line 1 column 189)
    at JSON.parse (<anonymous>)
    at parseCallArguments (/snapshot/copilot-intellij/lib/src/openai/stream.ts:836:21)
    at extractToolCalls (/snapshot/copilot-intellij/lib/src/openai/stream.ts:852:26)
    at convertToAPIJsonData (/snapshot/copilot-intellij/lib/src/openai/stream.ts:781:23)
    at prepareChatCompletionForReturn (/snapshot/copilot-intellij/lib/src/conversation/openai/stream.ts:29:35)
    at selector (/snapshot/copilot-intellij/lib/src/conversation/endpoint/ChatCompletionsEndpointStrategy.ts:207:13)
    at asyncIterableMap (/snapshot/copilot-intellij/lib/src/common/iterableHelpers.ts:6:15)
    at process.item (node:internal/process/task_queues:105:5)
    at chatCompletion (/snapshot/copilot-intellij/lib/src/common/iterableHelpers.ts:25:22)
    at As.processSuccessfulResponse (/snapshot/copilot-intellij/lib/src/conversation/chatMLFetcher.ts:531:26). Input: '{"filePath": "/home/xxx/workspaces/mylyn-main/git/org.eclipse.mylyn/mylyn.commons/org.eclipse.mylyn.commons.workbench/src/org/eclipse/mylyn/commons/workbench/forms/DatePickerPanel.java"'
    at parseCallArguments (/snapshot/copilot-intellij/lib/src/openai/stream.ts:841:15)
    at extractToolCalls (/snapshot/copilot-intellij/lib/src/openai/stream.ts:852:26)
    at convertToAPIJsonData (/snapshot/copilot-intellij/lib/src/openai/stream.ts:781:23)
    at prepareChatCompletionForReturn (/snapshot/copilot-intellij/lib/src/conversation/openai/stream.ts:29:35)
    at selector (/snapshot/copilot-intellij/lib/src/conversation/endpoint/ChatCompletionsEndpointStrategy.ts:207:13)
    at asyncIterableMap (/snapshot/copilot-intellij/lib/src/common/iterableHelpers.ts:6:15)
    at process.item (node:internal/process/task_queues:105:5)
    at chatCompletion (/snapshot/copilot-intellij/lib/src/common/iterableHelpers.ts:25:22)
    at As.processSuccessfulResponse (/snapshot/copilot-intellij/lib/src/conversation/chatMLFetcher.ts:531:26)
    at As.fetch (/snapshot/copilot-intellij/lib/src/conversation/chatMLFetcher.ts:488:28)