fix(diff): compare MaxLength, not MinLength, in CheckStringTypeChanges

[martel]

Hi, I've discovered this bug and let my Claude take it, fix and post this PR. I have close to zero Go familiarity myself, but the fix looks very simple. Hope that's okay.

Problem

CheckStringTypeChanges in diff/checks.go passes the MinLength fields to the MaxLength comparison:

maxLengthDiffs := CompareIntValues("MaxLength", type1.MinLength, type2.MinLength, WidenedType, NarrowedType)

This has two effects on diff.Compare:

• A change to minLength is reported twice, the second time labelled MaxLength. Adding minLength: 1, maxLength: 255 to a string property reports MinLength(1) and MaxLength(1) as AddedConstraint.
• A change to maxLength alone is never reported. Narrowing maxLength from 1000 to 255 on a request body property produces no difference, so a breaking change passes swagger diff unflagged.

The line has been like this since swagger diff was added to go-swagger in go-swagger/go-swagger#1961 (cmd/swagger/commands/diff/spec_analyser.go). It moved to checks.go in 2020 and to this repository in go-swagger/go-swagger#3308 without changing. go-swagger v0.36.6 depends on analysis v1.0.0, which has the bug.

Fix

Pass type1.MaxLength, type2.MaxLength. The change codes stay the same: a larger maxLength is WidenedType, a smaller one is NarrowedType.

Tests

TestCheckStringTypeChanges is new; the function had no direct test. It covers maxLength added, removed, narrowed and widened, minLength and maxLength added together, and a minLength change with maxLength unchanged. All six cases fail on the old line and pass with the fix.

• go test -race ./... and go test work pass.
• golangci-lint run ./diff/... reports nothing on the changed lines. It reports 7 issues that predate this change: one gofumpt in spec_analyser.go:927 and six modernize hints on floatPointerOf / intPointerOf in checks_test.go.

[fredbi]

Yeah good catch

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.24%. Comparing base (f20e430) to head (1598990).
⚠️ Report is 7 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #253      +/-   ##
==========================================
+ Coverage   94.21%   94.24%   +0.02%     
==========================================
  Files          29       29              
  Lines        3404     3404              
==========================================
+ Hits         3207     3208       +1     
+ Misses        193      192       -1     
  Partials        4        4              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

[fredbi]

It shows the the instructions left to the agents in this repo are useful!