Problem

Currently, when a pattern validation is added to a previously unrestricted parameter or property, oasdiff incorrectly classifies this as a WARN level change instead of an ERROR level breaking change.

This is problematic because:

• Adding a pattern restriction to a parameter that previously accepted any string value is a breaking change
• Existing clients that were sending values not matching the new pattern will start failing
• The current warning message is misleading and doesn't clearly indicate the severity

Example

Consider this OpenAPI change:

Before (example_before.yaml):

parameters:
  - name: cursor
    in: query
    description: Pagination cursor
    schema:
      type: string  # Accepts any string
      nullable: true
    required: false

After (example_after.yaml):

parameters:
  - name: cursor
    in: query
    description: Pagination cursor
    schema:
      type: string
      pattern: "^\\d+$"  # Now only accepts digits
      nullable: true
    required: false

This change will break existing clients that were sending non-digit cursor values, but was previously only flagged as a warning.

Solution

This PR implements proper severity classification for pattern-related changes:

1. Pattern Addition (pattern added): ERROR level

   • When a pattern is added to a previously unrestricted parameter/property
   • New specific error message: "This is a breaking change because adding a pattern restriction to a previously unrestricted parameter will reject values that were previously accepted, breaking existing clients"

2. Pattern Change (pattern changed): WARN level (unchanged)

   • When an existing pattern is changed to a different pattern
   • Keeps existing warning message since it's difficult to automatically determine if the new pattern is a superset

3. Pattern Generalization (pattern generalized): INFO level (unchanged)

   • When a pattern is changed to a more permissive one (e.g., to .*)

4. Pattern Removal (pattern removed): INFO level (unchanged)

   • When a pattern restriction is removed entirely

Changes Made

• Updated severity rules in checker/rules.go:
  • RequestParameterPatternAddedId: WARN → ERROR
  • RequestPropertyPatternAddedId: WARN → ERROR
• Added new localized error message pattern-added-error-comment for pattern additions
• Updated existing warning message pattern-changed-warn-comment to be more comprehensive
• Added multi-language support (English, Portuguese, Russian)
• Updated all relevant tests to reflect the new severity levels
• Fixed test ordering issues caused by the severity level changes

Verification

# Test with the provided example
make build
./bin/oasdiff breaking example_before.yaml example_after.yaml

# Expected output:
# 1 changes: 1 error, 0 warning, 0 info
# error [request-parameter-pattern-added] at example_after.yaml
#   in API GET /users
#     added the pattern '^\d+$' to the 'query' request parameter 'cursor'
#     This is a breaking change because adding a pattern restriction to a previously unrestricted parameter will reject values that were previously accepted, breaking existing clients

Backward Compatibility

This change only affects the severity classification of pattern additions. The detection logic remains the same, ensuring that:

1. No previously detected changes are missed
2. Only the severity level and error message change for pattern additions
3. All other pattern-related changes maintain their existing behavior