Handle OpenAPI schemas with format but no type keyword #7330

Copilot · 2026-01-27T19:02:50Z

Change from catch-all _ patterns to explicit type matching with or null
String formats (uuid, base64url, date-time, etc.) use (JsonSchemaType.String or null, "format")
Numeric formats use (JsonSchemaType.Number or JsonSchemaType.Integer or null, "format")
Add Integer type support for int16/int32 formats
Add changelog entry
Maintains compatibility with OpenAPI format registry
All 134 tests pass
Verified with real-world examples

Original prompt

This section details on the original issue you should resolve

<issue_title>Deal with missing type keyword</issue_title>
<issue_description>### What are you generating using Kiota, clients or plugins?

API Client/SDK

In what context or format are you using Kiota?

Nuget tool

Client library/SDK language

Csharp

Describe the bug

The OpenApi generator from Asp.NET started omitting the type keyword for DateTime properties starting with .NET 10:

"createdAt": {
-"type": "string",
"format": "date-time"
}

This results in UntypedNode being generated. This is legal according to the OAI spec and means "accept any object as long as it behaves like a date-time".

Expected behavior

We should probably default to string in that case.

How to reproduce

A schema like this:

 "Foo": {
    "type": "object",
    "properties": {
      "createdAt": {
        "type": "string",
        "format": "date-time"
      }
}

Open API description file

No response

Kiota Version

1.29.0

Latest Kiota version known to work for scenario above?(Not required)

No response

Known Workarounds

No response

Configuration

No response

Debug output

Click to expand log

```

</details>


### Other information

_No response_</issue_description>

<agent_instructions>Please investigate and propose a change to the KiotaBuilder.GetPrimitiveType method given that the format on the schema is optional and may not be present.

ensure that there is a fallback option for cases where the type is supplied without a format.

ensure that there is complete test coverage for all code paths</agent_instructions>

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

<comments>
<comment_new><author>@gavinbarron</author><body>
It's not clear how this is a kiota problem based on your report here. 

Is kiota failing to generate code that handles the field on the object correctly?
Or are you simply suggesting that we implement a default value of `string` internally for the `type` property of the field descriptor? </body></comment_new>
<comment_new><author>@gavinbarron</author><body>
If I've managed to understand the problem correctly we need to make a change in `KiotaBuilder.GetPrimitiveType` to accommodate this change in asp.net openapi generator.

at present we have a switch case with a case that looks like this for the `date-time` format.

```csharp
(JsonSchemaType.String, "date-time") => new CodeType { Name = "DateTimeOffset", IsExternal = true },

To accomplish this change I propose we drop the schemaType match and move it down the list so that it doesn't apply to numbers, integers, or booleans.

The next natural question; has the same thing happened for formats of time, date, or duration?

If so, we might end up with something like:

        return (typeName & ~JsonSchemaType.Null, format?.ToLowerInvariant()) switch
        {
            (_, "byte") => new CodeType { Name = "base64", IsExternal = true },
            (_, "binary") => new CodeType { Name = "binary", IsExternal = true },
            (JsonSchemaType.String, "base64url") => new CodeType { Name = "base64url", IsExternal = true },
            (JsonSchemaType.String, "uuid") => new CodeType { Name = "Guid", IsExternal = true },
            (JsonSchemaType.String, _) => new CodeType { Name = "string", IsExternal = true }, // covers commonmark and html
            (JsonSchemaType.Number, "double" or "float" or "decimal") => new CodeType { Name = format.ToLowerInvariant(), IsExternal = true },
            (JsonSchemaType.Number or JsonSchemaType.Integer, "int8") => new CodeType { Name = "sbyte", IsExternal = true },
            (JsonSchemaType.Number or JsonSchemaType.Integer, "uint8") => new CodeType { Name = "byte", IsExternal = true },
            (JsonSchemaType.Number or JsonSchemaType.Integer, "int64") => new CodeType { Name = "int64", IsExternal = true },
            (JsonSchemaType.Number, "int16") => new CodeType { Name = "integer", IsExternal = true },
            (JsonSchemaType.Number, "int32") => new CodeType { Name = "integer", IsExternal = true },
            (JsonSchemaType.Number, _) => new CodeType { Name = "double", IsExternal = true },
            (JsonSchemaType.Integer, _) => new CodeType { Name = "integer", IsExternal = true },
            (JsonSchemaType.Boolean, _) => new CodeType { Name = "boolean", IsExternal = true },
            (_, "duration") => new CodeType { Name = "TimeSpan", IsExternal = true },
            (_, "time") => new CodeType { Name = "TimeOnly", IsExternal = true },
            (_, "date") => new CodeType { Name = "DateOnly", IsExternal = true },
            (_, "date-time") => new CodeType { Name = "DateTimeOffset", IsExternal = true },
            (_, _) when !string.IsNullOrEmpty(childType) => new CodeType { Name = childType, IsExternal = false, },
            (_, _) => null,
 ...

</details>



<!-- START COPILOT CODING AGENT SUFFIX -->

- Fixes microsoft/kiota#7116

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Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

…ectly Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

gavinbarron · 2026-01-27T19:45:56Z

@copilot please expand this fix given that the type property is optional we could see format uuid without the type for example.

I expect that the format checks happen independent of the type checks, only using the type field as a fallback if no format has bee supplied

Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Copilot · 2026-01-27T19:54:13Z

@copilot please expand this fix given that the type property is optional we could see format uuid without the type for example.

I expect that the format checks happen independent of the type checks...

Expanded the fix in commit b863256. All format checks now happen independently of type, with type serving only as a fallback when format is absent or unrecognized. This includes uuid, base64url, and all numeric formats (int8, uint8, int16, int32, int64, double, float, decimal). Added 20 new test cases covering all supported formats without type.

src/Kiota.Builder/KiotaBuilder.cs

…tterns Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Copilot · 2026-01-29T01:01:54Z

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

https://api.github.com/repos/microsoft/kiota/releases
- Triggering command: /home/REDACTED/work/kiota/kiota/src/kiota/bin/Debug/net10.0/kiota /home/REDACTED/work/kiota/kiota/src/kiota/bin/Debug/net10.0/kiota generate -l csharp -d /tmp/test_datetime.yaml -o /tmp/kiota-output -n TestApi --clean-output (http block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

src/Kiota.Builder/KiotaBuilder.cs

baywet · 2026-01-29T14:28:41Z

Additionally, can you please add a changelog entry.

gavinbarron · 2026-01-29T20:15:41Z

@copilot please add a changelog entry for this fix

Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Copilot · 2026-01-29T20:18:31Z

@copilot please add a changelog entry for this fix

Added changelog entry in commit 4d9685c.

baywet

Thank you for making the changes!

baywet · 2026-01-29T20:25:21Z

@adrian05-ms to give it another review, since I handled conflicts, I can't give it the final review.

Initial plan

7f03364

Copilot AI assigned Copilot and gavinbarron Jan 27, 2026

Copilot started work on behalf of gavinbarron January 27, 2026 19:03 View session

Copilot AI and others added 2 commits January 27, 2026 19:07

Add support for missing type keyword with format in OpenAPI schemas

7b44871

Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Fix format-based type matching order to handle String|Null types corr…

f060950

…ectly Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix missing type keyword for DateTime properties~~ Handle OpenAPI schemas with format but no type keyword Jan 27, 2026

Copilot finished work on behalf of gavinbarron January 27, 2026 19:18

Copilot AI requested a review from gavinbarron January 27, 2026 19:18

Merge branch 'main' into copilot/fix-missing-type-keyword

c09e6cf

Copilot started work on behalf of gavinbarron January 27, 2026 19:48 View session

Copilot AI and others added 2 commits January 27, 2026 19:50

Make all format checks independent of type for comprehensive coverage

6ec8889

Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Add documentation for int16/int32 mapping to generic integer type

b863256

Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Copilot finished work on behalf of gavinbarron January 27, 2026 19:55

Merge branch 'main' into copilot/fix-missing-type-keyword

40e6149

gavinbarron marked this pull request as ready for review January 28, 2026 19:23

gavinbarron requested a review from a team as a code owner January 28, 2026 19:23

baywet requested changes Jan 28, 2026

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Copilot started work on behalf of gavinbarron January 29, 2026 00:58 View session

Use explicit type matching with null fallback instead of catch-all pa…

85646d5

…tterns Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Copilot finished work on behalf of gavinbarron January 29, 2026 01:02

gavinbarron approved these changes Jan 29, 2026

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baywet reviewed Jan 29, 2026

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src/Kiota.Builder/KiotaBuilder.cs Outdated Show resolved Hide resolved

Copilot started work on behalf of gavinbarron January 29, 2026 20:16 View session

Add Integer type support for int16/int32 formats and changelog entry

4d9685c

Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Copilot AI requested a review from gavinbarron January 29, 2026 20:18

Copilot finished work on behalf of gavinbarron January 29, 2026 20:19

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Merge branch 'main' into copilot/fix-missing-type-keyword

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Handle OpenAPI schemas with format but no type keyword #7330

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In what context or format are you using Kiota?

Client library/SDK language

Describe the bug

Expected behavior

How to reproduce

Open API description file

Kiota Version

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Known Workarounds

Configuration

Debug output

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Copilot AI commented Jan 27, 2026 •

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