Map [MinLength]/[MaxLength] on dictionary properties to minProperties / maxProperties

[KitKeen]

Fixes #3915.

Problem

Applying [MinLength(1)] to a property typed as a dictionary (IDictionary<,>, IReadOnlyDictionary<,>, etc.) produces "minLength": 1 on the generated schema:

public class MyModel
{
    [Required]
    [MinLength(1)]
    public IReadOnlyDictionary<string, string?> Values { get; init; }
}

"minLength" on an object schema is invalid per the OpenAPI 3.x spec — it's defined only for string schemas. Linters such as vacuum flag this (the original reporter hit it exactly that way). The equivalent constraint for object schemas is "minProperties".

Fix

OpenApiSchemaExtensions.Apply{Min,Max,}LengthAttribute already branches on schema.Type to pick MinItems / MaxItems for arrays. This PR adds a parallel branch for JsonSchemaTypes.Object so dictionary schemas get MinProperties / MaxProperties instead of the meaningless MinLength / MaxLength.

No changes to the MinLengthRouteConstraint / MaxLengthRouteConstraint handlers — route parameters are primitives and cannot be dictionaries, so the existing Array/otherwise split is correct there.

Before / after

public class MyModel
{
    [Required]
    [MinLength(1)]
    public IReadOnlyDictionary<string, string?> Values { get; init; }
}

Before:

"MyModel": {
  "type": "object",
  "required": [ "values" ],
  "properties": {
    "values": {
      "type": "object",
      "additionalProperties": { "type": "string", "nullable": true },
      "minLength": 1
    }
  }
}

After:

"MyModel": {
  "type": "object",
  "required": [ "values" ],
  "properties": {
    "values": {
      "type": "object",
      "additionalProperties": { "type": "string", "nullable": true },
      "minProperties": 1
    }
  }
}

Tests

Added to OpenApiSchemaExtensionsTests:

• MinLength on dictionary schema → minProperties
• MaxLength on dictionary schema → maxProperties
• Length(min,max) on dictionary schema → min+maxProperties
• Regression guards: MinLength on string schema still maps to minLength; on array schema still maps to minItems.

Scope

• No public API changes.
• No dependency changes.
• Behavior change is limited to schemas whose Type includes Object — previously those would receive MinLength/MaxLength, which was invalid per the OpenAPI spec, so any consumer relying on the old output was already producing non-conforming documents.

Checklist

• Bug fix includes a test that fails without the fix.
• No public API surface change.
• Builds & tests pass locally. (Local SDK is 8.0; repo requires 10.0 — relying on CI.)

[martincostello]

Please make some test changes to that the OpenAPI snapshots demonstrate the required changes to the generated OpenAPI schemas.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.05%. Comparing base (d22870e) to head (54c1cee).
⚠️ Report is 61 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3922   +/-   ##
=======================================
  Coverage   95.04%   95.05%           
=======================================
  Files         111      111           
  Lines        3958     3965    +7     
  Branches      801      804    +3     
=======================================
+ Hits         3762     3769    +7     
  Misses        196      196           

Flag	Coverage Δ
Linux	95.05% <100.00%> (+<0.01%)	⬆️
Windows	95.05% <100.00%> (+<0.01%)	⬆️
macOS	95.05% <100.00%> (+<0.01%)	⬆️

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[martincostello]

Tests are failing.

[KitKeen]

@martincostello pushed 2d8e31e - the snapshot rework (743061c) only added baselines under snapshots/10_0/, so the test failed on net8.0/9.0. Now mirrored to 8_0/ and 9_0/ (schemas are framework-agnostic; verified against the other snapshots in this repo). Could you re-approve the workflows? Thanks!

[KitKeen]

Pushed 54c1cee. The earlier fix in 2d8e31e (copying snapshots to 8_0/ and 9_0/) brought macos-latest and ubuntu-latest green, but windows-latest kept failing with git checkout errors of the form error: unable to create file ... : Filename too long. The cause was the Theory parameter Type type being serialized into the snapshot filename via .UseParameters(type), producing names like ..._type=Swashbuckle.AspNetCore.TestSupport.TypeWithValidationAttributesViaMetadataType.verified.txt. Combined with the Windows runner checkout root and the snapshots/<fw>/ segment the total exceeded the 260-character MAX_PATH limit.

This commit replaces .UseParameters(type) with .UseTextForParameters(type.Name) so only the short type name (without the Swashbuckle.AspNetCore.TestSupport. namespace) appears in the filename, and renames the six existing snapshots accordingly. Snapshot contents are unchanged.

[github-actions]

Thanks for your contribution @KitKeen - the changes from this pull request have been published as part of version 10.2.2 📦, which is now available from NuGet.org 🚀