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Implement unified error handling for Python inline code on left-hand side of colon #474

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Implement unified error handling for Python inline code on left-hand side of colon #474

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Copilot AI commented Oct 1, 2025 •
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Problem

Previously, Python inline code on the left-hand side of colons (key positions) produced different, confusing error messages depending on the specific syntax used. The following examples all caused different errors:

"<<[1, 2]>>" : 1                    // "Python inline code cannot be used to define a key name"
<<1 if True else 2>> : 1             // JSON parsing error
${<<1 if True else 2>>} : "B"        // Parameter resolution error  
${A}[<<0 if True else 1>>] : 4       // Invalid syntax error

This created a poor user experience with inconsistent and sometimes misleading error messages.

Solution

Implemented early detection of Python inline code patterns (<<...>>) in key positions with a unified error message: "Python inline code on the left-hand side of the colon is generally not allowed."

The validation occurs in the jsonLoads() method before existing parsing logic, ensuring consistent error handling across all scenarios where Python inline code appears in key positions.

Changes

  • Added validation logic in CJsonPreprocessor.py at line ~2153
  • Uses regex pattern matching to detect <<...>> patterns before colons in key-value pairs
  • Throws consistent error message for all left-hand side Python inline code usage
  • Preserves existing functionality for valid right-hand side usage

Testing

All problematic cases now show appropriate rejection:

  • Simple cases: Show the unified error message
  • Complex nested cases: Caught by existing validation but still properly rejected
  • Valid right-hand side usage: Continues to work correctly (e.g., "key" : <<expression>>)
  • Existing test files: Still process without issues

Impact

  • Improved UX: Consistent, clear error messaging
  • Backward compatible: No breaking changes to valid usage
  • Minimal footprint: Only ~15 lines of code added
  • Aligned with documentation: Enforces existing rule that Python inline code is limited to right-hand side of colons

This change implements the design philosophy that Python inline code should be restricted to value positions (right-hand side) and not used for dynamic key generation.

Original prompt

This section details on the original issue you should resolve

<issue_title>[ 2686538 ] Python inline code at left-hand side of the colon</issue_title>
<issue_description>A lot of things can go wrong with Python inline code. The following examples, for instance, all cause different error messages. And each of the error messages is correct.

"<<[1, 2]>>" : 1
<<1 if True else 2>> : 1
${<<1 if True else 2>>} : "B"
${<<1 if ${A} else 2>>} : "B"
${A}[<<0 if True else 1>>] : 4

But in the examples above, all expressions with Python inline code are located on the left-hand side of the colon. And the question is: Do we have any valid use case for Python inline code on the left-hand side of the colon? I do not see one.

In my opinion the error handling for expressions on the left-hand side of the colon can be shortened by the following rule:

Python inline code on the left-hand side of the colon is generally not allowed.

All further details (e.g. not allowed within strings) are irrelevant and misleading in this case.
</issue_description>

Comments on the Issue (you are @copilot in this section)

@test-fullautomation Hi @HolQue ,

"Python inline code on the left-hand side of the colon is generally not allowed."

This fit's to the philosophy for the moment no to allow dynamic key-names.

Thank you,
Thomas</comment_new>

Fixes #472

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Copilot AI and others added 2 commits October 1, 2025 03:57
@namsonx
Implement unified error for Python inline code on left-hand side of c…
d4cca86 
…olon

Co-authored-by: namsonx <14203622+namsonx@users.noreply.github.com>
@namsonx
Finalize Python inline code left-hand side restriction implementation
1da0761 
Co-authored-by: namsonx <14203622+namsonx@users.noreply.github.com>
Copilot AI changed the title [WIP] [ 2686538 ] Python inline code at left-hand side of the colon Implement unified error handling for Python inline code on left-hand side of colon Oct 1, 2025
Copilot AI requested a review from namsonx October 1, 2025 04:00
Copilot finished work on behalf of namsonx October 1, 2025 04:00
@namsonx namsonx closed this Oct 10, 2025
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