fix: Enhance error handling for langchain-core version compatibility

[ogabrielluiz]

Improve error handling by checking for langchain-core version compatibility and providing clear guidance when incompatibility is detected. This change aims to assist users in resolving issues related to version mismatches.

Summary by CodeRabbit

• Bug Fixes
  • Enhanced error handling for langchain-core version compatibility. The CLI now detects version conflicts intelligently and delivers clear, targeted guidance messages to help you quickly identify and resolve compatibility issues when they arise.

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Walkthrough

A new helper function _check_langchain_version_compatibility() detects langchain-core version incompatibilities and returns user-facing guidance messages. The output_error() function was enhanced to invoke this checker and replace error messages with compatibility guidance when applicable, propagating these messages into JSON error responses.

Changes

Cohort / File(s)	Summary
LangChain compatibility error handling src/lfx/src/lfx/cli/run.py	Added _check_langchain_version_compatibility() helper function to detect version incompatibilities from error messages; modified output_error() to call the checker and conditionally replace error and exception messages with compatibility-driven guidance in JSON responses

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

• Verify that the langchain version compatibility detection logic correctly parses error messages and returns appropriate guidance
• Confirm that the compatibility message replacement in output_error() doesn't interfere with existing verbose output or logging behavior
• Check that JSON error responses are properly formatted when compatibility messages are substituted

Possibly related PRs

• fix: enhance error handling in run command by restoring original stdout/stderr before outputting error messages #10186: Modifies error handling in src/lfx/cli/run.py by restoring stdout/stderr before calling output_error(), which interacts with the same error output pipeline being enhanced in this PR.

Suggested labels

bug, lgtm

Suggested reviewers

• erichare
• edwinjosechittilappilly

Pre-merge checks and finishing touches

Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error, 2 warnings)

Check name	Status	Explanation	Resolution
Test Coverage For New Implementations	❌ Error	PR adds new version compatibility checking logic but includes no test files to verify the new _check_langchain_version_compatibility() function or modified output_error() function.	Add test file with test cases for the new compatibility checker function and modified error output logic to ensure correctness and prevent regressions.
Test Quality And Coverage	⚠️ Warning	The pull request introduces a new helper function _check_langchain_version_compatibility() and modifies output_error() but lacks corresponding test coverage.	Add comprehensive test coverage including unit tests for _check_langchain_version_compatibility(), integration tests for output_error(), and JSON response validation.
Test File Naming And Structure	⚠️ Warning	PR adds version compatibility checking function but lacks test coverage for new functionality.	Create test file with comprehensive test cases for langchain version compatibility detection and error handling integration.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: enhancing error handling with langchain-core version compatibility detection.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Excessive Mock Usage Warning	✅ Passed	PR modifies production code in run.py to enhance langchain-core version compatibility error handling without introducing test files or mock-based patterns.

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (2)

src/lfx/src/lfx/cli/run.py (2)

27-57: Compatibility helper is solid; consider de‑duplicating condition and centralizing version ranges

The detection logic and lazy import are appropriate, and the user-facing message is very helpful. Two small refinements you might consider:

• The condition if "langchain_core.memory" in error_message or "No module named 'langchain_core.memory'" in error_message: is redundant, since the second string already contains the first; you can drop the explicit No module named ... branch.
• The hard-coded ranges (langchain-core>=0.3.0,<1.0.0, langchain-openai>=0.3.0,<1.0.0, langchain-community>=0.3.0,<1.0.0) and suggested commands could drift from the officially supported versions / packaging metadata over time; consider pulling these from a single source of truth (e.g., config/metadata) or at least adding a small comment pointing to where they must be kept in sync.

Example of a minimal code tweak for the condition:

-    if "langchain_core.memory" in error_message or "No module named 'langchain_core.memory'" in error_message:
+    if "langchain_core.memory" in error_message:

Please double-check that the version ranges and install commands here match your actual supported matrix and dependency pins elsewhere in the repo.

---

60-87: Reuse error_str as single source of truth for JSON exception_message

error_str is computed and even updated in the compatibility branch, but never used when building error_response. You can simplify and avoid duplication by using error_str consistently:

 def output_error(error_message: str, *, verbose: bool, exception: Exception | None = None) -> None:
     """Output error in JSON format to stdout when not verbose, or to stderr when verbose."""
-    # Check for known compatibility issues and provide helpful messages
-    error_str = str(exception) if exception else error_message
-    compatibility_msg = _check_langchain_version_compatibility(error_str)
-
-    if compatibility_msg:
-        error_message = compatibility_msg
-        if exception:
-            # Update exception message for JSON output
-            error_str = compatibility_msg
+    # Check for known compatibility issues and provide helpful messages
+    error_str = str(exception) if exception else error_message
+    compatibility_msg = _check_langchain_version_compatibility(error_str)
+
+    if compatibility_msg:
+        # Use the compatibility message consistently for both human and JSON output
+        error_str = error_message = compatibility_msg
@@
-    if exception:
-        error_response["exception_type"] = type(exception).__name__
-        if compatibility_msg:
-            error_response["exception_message"] = compatibility_msg
-        else:
-            error_response["exception_message"] = str(exception)
-    else:
-        error_response["exception_message"] = error_message
+    if exception:
+        error_response["exception_type"] = type(exception).__name__
+        error_response["exception_message"] = error_str
+    else:
+        error_response["exception_message"] = error_message

This keeps behavior the same while removing dead code and guaranteeing the JSON payload always reflects whatever message you decided to surface (raw exception vs. compatibility guidance).

📜 Review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 7524379 and 709486f.

📒 Files selected for processing (1)

• src/lfx/src/lfx/cli/run.py (2 hunks)

[github-actions]

Frontend Unit Test Coverage Report

Coverage Summary

Lines	Statements	Branches	Functions
	15.53% (4261/27421)	8.73% (1834/20999)	9.75% (589/6037)

Unit Test Results

Tests	Skipped	Failures	Errors	Time
1675	0 💤	0 ❌	0 🔥	21.132s ⏱️

[codecov]

Codecov Report

❌ Patch coverage is 45.83333% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 33.05%. Comparing base (b6ed2bc) to head (936ae87).

Files with missing lines	Patch %	Lines
src/lfx/src/lfx/cli/run.py	27.77%	10 Missing and 3 partials ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##           release-1.7.0   #10768   +/-   ##
==============================================
  Coverage          33.05%   33.05%           
==============================================
  Files               1368     1368           
  Lines              63815    63832   +17     
  Branches            9391     9395    +4     
==============================================
+ Hits               21093    21099    +6     
- Misses             41679    41687    +8     
- Partials            1043     1046    +3     

Flag	Coverage Δ
backend	52.78% <100.00%> (+0.01%)	⬆️
frontend	14.37% <ø> (ø)
lfx	40.01% <27.77%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/backend/base/langflow/services/deps.py	83.33% <100.00%> (ø)
src/lfx/src/lfx/cli/run.py	71.20% <27.77%> (-2.65%)	⬇️

... and 3 files with indirect coverage changes

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[ogabrielluiz]

@Adam-Aghili This is a fix for 1.7.0

[mpawlow]

@ogabrielluiz

Code Review 1

• Approved / LGTM
• See PR comments: (a) to (c)
  • All Minor severity

[mpawlow]

(a) [Minor] Helpful / detailed / verbose error message contains hardcoded dependency version ranges for various libraries

• Excellent message & tactical fix; but, wondering if these version ranges / libraries will become out of date in the future and need to be updated
• This is a Minor severity issue. Please feel free to ignore or optionally address.

[ogabrielluiz]

Since this error will only occur is this specific case happens, I think we are fine to keep it like that, then remove it later once we support 1.0

[mpawlow]

(b) [Minor] Langchain version compatibility is checked retroactively after an error has occurred

• Wondering if Langchain version compatibility could be checked proactively at runtime (if it wouldn't degrade performance)
• Ideally, an external manifest could be used / enforced to outline the semver range requirements (but I'm not yet familiar with the architecture)
• This is a Minor severity issue. Please feel free to ignore or optionally address.

[mpawlow]

(c) [Minor] Suggest including the original error message in the compatibility message rather than discarding it

• However, I'm not sure if there is any value in that or if that would be redundant
• This is a Minor severity issue. Please feel free to ignore or optionally address.

[Adam-Aghili]

LGTM

[Adam-Aghili]

Union vs |

[Adam-Aghili]

Union is needed in import