Fix #4656: Improve diagnostics for invalid proto files

[ARYPROGRAMMER]

Fixes ballerina-platform/ballerina-library#4656 - Improves error diagnostics when bal grpc command processes invalid proto files.

Problem: When processing invalid proto files, the command crashed with unhelpful IOException: Stream closed errors instead of displaying the actual protoc compiler error messages.

Root Cause: The handleProcessExecutionErrors() method was checking the process exit value before reading the error stream, causing the stream to close prematurely.

Solution:

• Read error stream BEFORE checking process exit value to prevent stream closure
• Added formatProtoError() helper method to format user-friendly error messages
• Errors now include file name, line number, and clear descriptions from protoc

Examples

Before (Bad):

SEVERE: An error occurred when generating the proto descriptor.
io.ballerina.protoc.protobuf.exception.CodeGeneratorException: Invalid command syntax. Stream closed
    at io.ballerina.protoc.protobuf.utils.BalFileGenerationUtils.handleProcessExecutionErrors(...)
Caused by: java.io.IOException: Stream closed

After

Error: Failed to generate Ballerina files from proto definition.

Proto compilation failed with the following error:
user_service.proto:3:14: "User" is not defined.
user_service.proto:4:14: "Pagination" is not defined.

Please check your .proto file for syntax errors and undefined types.

Test Cases

• Undefined message types: Shows clear "Type is not defined" messages
• Syntax errors: Shows specific line/column with syntax issue
• Valid protos: Continue to work correctly (regression test)

Checklist

• Linked to an issue (Improve diagnostics for invalid proto files ballerina-library#4656)
• Updated the changelog
• Added tests
• Updated the spec

[CLAassistant]

All committers have signed the CLA.

[ARYPROGRAMMER]

@daneshk can you please review this

[daneshk]

@daneshk can you please review this

@ARYPROGRAMMER Seems like we have duplicate methods. Shall we have one?

[ARYPROGRAMMER]

@daneshk can you please review this

@ARYPROGRAMMER Seems like we have duplicate methods. Shall we have one?

Give me some time I'll just see once

[ARYPROGRAMMER]

@daneshk can you please review this

@ARYPROGRAMMER Seems like we have duplicate methods. Shall we have one?

yeah saw that lgtm now

@daneshk

[daneshk]

@ARYPROGRAMMER I just went through the original code. We mistakenly duplicate whole BalFileGenerationUtils.java inside the utils package. we should remove the one in the utils package and use the one in the core package. Shall we do it in the same PR? So that we need one place do the change.

[ARYPROGRAMMER]

@ARYPROGRAMMER I just went through the original code. We mistakenly duplicate whole BalFileGenerationUtils.java inside the utils package. we should remove the one in the utils package and use the one in the core package. Shall we do it in the same PR? So that we need one place do the change.

yes absolutely we can do that. just check once my changes in few minutes

[ARYPROGRAMMER]

@daneshk i have did exactly what you wanted. let's see if this this you like it

[ARYPROGRAMMER]

@daneshk this should fix the checkstyle error

[ARYPROGRAMMER]

really worked hard on this, glad to contribute - hope this time everything is resolved

[codecov]

Codecov Report

❌ Patch coverage is 46.66667% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.40%. Comparing base (abc9b95) to head (5cf0ebb).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
.../ballerina/protoc/core/BalFileGenerationUtils.java	46.66%	15 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #72      +/-   ##
============================================
+ Coverage     84.39%   86.40%   +2.01%     
+ Complexity      656      655       -1     
============================================
  Files            57       56       -1     
  Lines          3312     3243      -69     
  Branches        376      361      -15     
============================================
+ Hits           2795     2802       +7     
+ Misses          414      338      -76     
  Partials        103      103              

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[ARYPROGRAMMER]

let me know if anything needed here, thanks @daneshk

[ARYPROGRAMMER]

can this be merged today @daneshk

[daneshk]

LGTM

[daneshk]

@ARYPROGRAMMER Thanks for the contribution.