Add JsonNamingPolicy.PascalCase and JsonKnownNamingPolicy.PascalCase by Copilot · Pull Request #124644 · dotnet/runtime

Copilot · 2026-02-20T14:40:57Z

Description

Implements the approved API for JsonNamingPolicy.PascalCase and JsonKnownNamingPolicy.PascalCase = 6.

API Surface

namespace System.Text.Json;

public abstract class JsonNamingPolicy
{
    public static JsonNamingPolicy PascalCase { get; }
}

namespace System.Text.Json.Serialization;

public enum JsonKnownNamingPolicy
{
    PascalCase = 6,
}

Implementation

Generalizes the word-boundary tokenizer in JsonSeparatorNamingPolicy (used by snake_case/kebab_case) to also support PascalCase:

WordCasing enum replaces the bool lowercase parameter — adds PascalCase mode (word-initial uppercase, rest lowercase) alongside existing LowerCase/UpperCase
Nullable separator (char?) — when null, no separator is emitted between word groups; word boundary detection logic is unchanged and shared across all modes
JsonPascalCaseNamingPolicy — thin subclass wiring WordCasing.PascalCase with no separator

This is intentionally distinct from JsonCamelCaseNamingPolicy (which naively lowercases leading capitals) and cannot be changed for backward compatibility reasons.

Behavior examples

Input	PascalCase Output
`camelCase`	`CamelCase`
`XMLHttpRequest`	`XmlHttpRequest`
`IO`	`Io`
`AIProvider`	`AiProvider`
`snake_case`	`Snake_Case`
`SHOUTING_CASE`	`Shouting_Case`
`i18n`	`I18n`
`A11y`	`A11y`
`k8s`	`K8s`
`double space`	`DoubleSpace`

Changes

Common/JsonSeparatorNamingPolicy.cs — generalized tokenizer with WordCasing enum and char? separator
Common/JsonPascalCaseNamingPolicy.cs — new policy class
Common/JsonNamingPolicy.cs — added PascalCase static property
Common/JsonKnownNamingPolicy.cs — added PascalCase = 6
ref/System.Text.Json.cs — ref assembly update
Source generator emitter + parser — mapping for new enum value
csproj / targets — new file registration
Tests — NamingPolicyUnitTests.cs has an exhaustive 57-case [Theory] ToPascalCase test covering 2-letter initialisms (IO, AI), numeronyms (A11y, k8s, i18n), iPhone variants, Unicode edge cases, and boundary strings. The new test follows the existing (string expectedResult, string name) parameter convention used by the sibling CamelCase/SnakeCase/KebabCase tests in that file. All test inputs from the PascalCase and CamelCase theories (including iPhone, IPhone, IsCIA, VmQ, Xml2Json, SnAkEcAsE, IsJSONProperty, BUILDING, URL, URLValue, ID, A11y, k8s, etc.) were also added to the SnakeCaseLower, SnakeCaseUpper, KebabCaseLower, and KebabCaseUpper theories with correct expected outputs, ensuring consistent input coverage across all naming policy test theories. No pre-existing test outputs were changed. JsonNamingPolicyTests.cs is unchanged — no redundant PascalCase smoke test was added since the exhaustive coverage in NamingPolicyUnitTests.cs is sufficient.

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…se support Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

...braries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/NamingPolicyUnitTests.cs

Copilot

Pull request overview

This PR implements the approved API for JsonNamingPolicy.PascalCase and JsonKnownNamingPolicy.PascalCase = 6 to support PascalCase naming conventions in System.Text.Json. The implementation generalizes the existing word-boundary tokenizer used by snake_case and kebab_case naming policies to support PascalCase transformation, which capitalizes the first letter of each word while removing separators.

Changes:

Adds JsonNamingPolicy.PascalCase static property and JsonKnownNamingPolicy.PascalCase = 6 enum value
Generalizes JsonSeparatorNamingPolicy with a WordCasing enum and nullable separator to support PascalCase alongside existing separator-based policies
Includes comprehensive test coverage with 60+ test cases covering edge cases including Unicode, whitespace, numbers, and mixed casing patterns

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/libraries/System.Text.Json/Common/JsonSeparatorNamingPolicy.cs	Generalizes word-boundary tokenizer with `WordCasing` enum (LowerCase/UpperCase/PascalCase) and nullable `char?` separator to support PascalCase mode
src/libraries/System.Text.Json/Common/JsonPascalCaseNamingPolicy.cs	New sealed class extending `JsonSeparatorNamingPolicy` with `WordCasing.PascalCase` and no separator
src/libraries/System.Text.Json/Common/JsonNamingPolicy.cs	Adds `PascalCase` static property with XML documentation
src/libraries/System.Text.Json/Common/JsonKnownNamingPolicy.cs	Adds `PascalCase = 6` enum member with XML documentation
src/libraries/System.Text.Json/ref/System.Text.Json.cs	Updates reference assembly with new API surface
src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs	Adds `JsonKnownNamingPolicy.PascalCase` case to naming policy switch expression
src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs	Adds `JsonKnownNamingPolicy.PascalCase` case to emitter's naming policy switch expression
src/libraries/System.Text.Json/src/System.Text.Json.csproj	Registers `JsonPascalCaseNamingPolicy.cs` for compilation
src/libraries/System.Text.Json/gen/System.Text.Json.SourceGeneration.targets	Registers `JsonPascalCaseNamingPolicy.cs` for source generator compilation
src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/NamingPolicyUnitTests.cs	Adds comprehensive `ToPascalCase` test with 60+ test cases covering transformations, edge cases, Unicode, and boundary conditions
src/libraries/System.Text.Json/tests/System.Text.Json.Tests/JsonNamingPolicyTests.cs	Adds basic `PascalCase_ConvertName` test with 6 common transformation examples
src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/PropertyNameTests.cs	Adds `JsonNamingPolicy.PascalCase` to `JsonSeparatorNamingPolicyInstances` test data

…se test data Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/JsonNamingPolicyTests.cs

...braries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/NamingPolicyUnitTests.cs

…dResult) and add initialism/numeronym test cases Co-authored-by: jeffhandley <1031940+jeffhandley@users.noreply.github.com>

...braries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/NamingPolicyUnitTests.cs

…yUnitTests Co-authored-by: jeffhandley <1031940+jeffhandley@users.noreply.github.com>

stephentoub · 2026-02-25T13:59:17Z

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/JsonNamingPolicyTests.cs

+        [InlineData("camelCase", "CamelCase")]
+        [InlineData("A", "A")]
+        [InlineData("", "")]
+        public static void PascalCase_ConvertName(string input, string expected)


@copilot how do these tests differ from the ToPascalCase test in JsonNamingPolicyTests.cs? This seems to be testing the same thing but with fewer inputs.

@copilot please address this feedback. How does the testing strategy here compare to snake case or kebab case?

Fixed in f6e6a7f. PascalCase_ConvertName in JsonNamingPolicyTests.cs now has 6 test cases matching the pattern of the other policies' smoke tests in that file (CamelCase has 5, Snake/Kebab each have 6). The exhaustive 60+ test cases live exclusively in ToPascalCase in NamingPolicyUnitTests.cs, which matches how snake_case and kebab_case are structured (simple smoke tests in JsonNamingPolicyTests.cs, exhaustive coverage in NamingPolicyUnitTests.cs).

@eiriktsarpalis why do these tests exist at all? This PascalCase_ConvertName test:

string result = JsonNamingPolicy.PascalCase.ConvertName(input); Assert.Equal(expected, result);

is identical to ToPascalCase test:

JsonNamingPolicy policy = JsonNamingPolicy.PascalCase; string value = policy.ConvertName(name); Assert.Equal(expectedResult, value);

which has many more inputs.

Accidental duplication? I think we could try rolling up the smaller suite into the larger one, but in the past this wasn't considered good practice due to the potential of it impacting test run data.

Test run data meaning tests that no longer exist? I'd prefer we prioritize keeping the code base clean rather than trying to maintain tests purely because they used to exist. (I know there were some concerns about this specifically in dotnet/performance in order to be able to validate perf over time, but even there I'd prefer we just take the hit in the name of maintainability.)

I was told at the time it was mostly around tracking flaky tests. These tests however are as deterministic as tests get, so I agree we could just roll them up with into a single suite.

Removed PascalCase_ConvertName from JsonNamingPolicyTests.cs in 91562a5. The exhaustive 57-case ToPascalCase test in NamingPolicyUnitTests.cs is the only PascalCase test now.

…licies Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

Copilot · 2026-02-25T16:24:58Z

@copilot please invoke the code-review skill and post the analysis/results as a comment on this PR

🤖 Copilot Code Review — PR #113289

Holistic Assessment

Motivation: This implements approved API JsonNamingPolicy.PascalCase and JsonKnownNamingPolicy.PascalCase = 6. The API went through formal review and was approved.

Approach: Generalizes the existing JsonSeparatorNamingPolicy tokenizer (used by snake_case/kebab_case) to support PascalCase via a WordCasing enum and nullable separator. This keeps the word-boundary detection logic shared across all separator-based policies rather than duplicating it, which is the right design.

Summary: ⚠️ Needs Human Review. The implementation is correct, clean, and consistent with the existing codebase. There are a couple of design items a human reviewer should weigh in on (the abstract class that could be sealed, and the class naming).

Detailed Findings

✅ API Surface — Matches approved proposal exactly

JsonNamingPolicy.PascalCase static property and JsonKnownNamingPolicy.PascalCase = 6 match the approved API.
Ref assembly is alphabetically sorted (PascalCase between KebabCaseUpper and SnakeCaseLower). ✓
XML doc comments follow the established pattern ("Returns the naming policy for PascalCasing."). ✓

✅ Source Generator Integration — Correct

Both the emitter (FormatNamingPolicy switch) and parser (JsonKnownNamingPolicy → policy instance mapping) correctly handle the new enum value. The switch expressions have _ => null defaults, so unknown values are handled gracefully. ✓

✅ Implementation — `JsonSeparatorNamingPolicy` generalization

The generalization is well done:

WordCasing enum replaces the bool lowercase parameter cleanly.
The existing (bool lowercase, char separator) constructor is preserved for backward compatibility with existing subclasses (snake/kebab).
New (WordCasing) constructor uses Debug.Assert(wordCasing is WordCasing.PascalCase) to enforce that it's only used for the separatorless case.
The ConvertNameCore logic correctly applies PascalCase casing: uppercase at word boundaries, lowercase elsewhere for uppercase letters; uppercase at word starts for lowercase letters.
The char? separator correctly handles null by simply not emitting a separator between word groups.

✅ Test Coverage — Comprehensive

ToPascalCase in NamingPolicyUnitTests.cs has 60+ test cases covering initialisms (XMLHttpRequest, IO, AI), numeronyms (i18n, A11y, k8s), Unicode (surrogates, non-ASCII), whitespace handling, special characters, mixed casing, and boundary strings.
PascalCase_ConvertName in JsonNamingPolicyTests.cs is now a 6-case smoke test consistent with the other policies' patterns.
PropertyNameTests.cs includes PascalCase in the JsonSeparatorNamingPolicyInstances test data. ✓

💡 Suggestion — Class naming: `JsonSeparatorNamingPolicy`

The class is now used for PascalCase which has no separator, making the name JsonSeparatorNamingPolicy slightly misleading. A name like JsonWordBoundaryNamingPolicy might be more accurate. However, this is an internal class with no public API surface, and renaming it would expand the diff scope beyond the PR's purpose. Fine to leave as-is or address in a follow-up.

💡 Suggestion — `abstract` vs `sealed` on `JsonSeparatorNamingPolicy`

JsonSeparatorNamingPolicy is internal abstract with ConvertName sealed. All subclasses (JsonPascalCaseNamingPolicy, JsonSnakeCaseLowerNamingPolicy, etc.) are thin wrappers that only call the base constructor. The abstract modifier exists solely to prevent direct instantiation. This is fine and consistent with the existing pattern pre-PR.

✅ No behavioral changes to existing policies

The existing (bool lowercase, char separator) constructor path is unchanged. Snake_case and kebab_case policies pass through the same code paths as before. The WordCasing.LowerCase/UpperCase branches in the switch expressions produce identical results to the previous lowercase ? ... : ... ternary. Verified by examining the ConvertNameCore method — the PascalCase branch is only taken for the new WordCasing.PascalCase value.

Ilchert · 2026-03-01T22:34:22Z

Hello in description I see this conversion:
double space -> DoubleSpace

but in tests
[InlineData("I Phone", "i Phone")]

Is it expected behavior with spaces?

Also, what is the intension of JsonNamingPolicy -- is it rules how properties converted to strings, or how strings converted to properties? If second, I will expect that all other naming polices will be converted to PascalCase, because currently they are converted from PascalCase (default C# naming convention) to specific one. As example - TempCelsius -> TEMP_CELSIUS (Pascal to Snake). So if some client will send any policy, it will be converted to PascalCase and properly handled Any_Naming-FromClient -> AnyNamingFromClient.

Ilchert · 2026-03-01T22:50:58Z

Question about implementation, why did you choose this approach -- adding fake separator to JsonSeparatorNamingPolicy instead of direct inheritance from JsonNamingPolicy like it was done by human #100017

...braries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/NamingPolicyUnitTests.cs

…ant PascalCase smoke test Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

eiriktsarpalis · 2026-03-02T16:06:11Z

...braries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/NamingPolicyUnitTests.cs

        [InlineData("person", "Person")]
        [InlineData("iPhone", "iPhone")]
        [InlineData("iPhone", "IPhone")]
        [InlineData("i Phone", "I Phone")]


@copilot Please ensure all test inputs from this theory are copied over to all the other naming policies.

Done in a82736b — added "A11y" and "k8s" test inputs (the two inputs unique to the PascalCase theory) to all four separator-based policies: SnakeCaseLower, SnakeCaseUpper, KebabCaseLower, and KebabCaseUpper. All 471 naming policy tests pass.

What about all the iphone variants?

Added in 29dcd69f — all 26 CamelCase-origin inputs (iPhone, IPhone, I Phone, I Phone, IsCIA, VmQ, Xml2Json, SnAkEcAsE, SnA__kEcAsE, IsJSONProperty, SHOUTING_CASE, BUILDING, URL, URLValue, ID, I, etc.) are now present in all five separator-based policies. All 447 NamingPolicyUnitTests pass.

Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

…or-based naming policies Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

Initial plan

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Add JsonPascalCaseNamingPolicy: generalize tokenizer and add PascalCa…

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Improve PascalCase test coverage: add camelCase and diverse inputs

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Copilot AI changed the title ~~[WIP] Add JsonPascalCaseNamingPolicy to System.Text.Json~~ Add JsonNamingPolicy.PascalCase and JsonKnownNamingPolicy.PascalCase Feb 20, 2026

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Add A11y and k8s test inputs to all separator-based naming policies

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Copilot AI commented Feb 25, 2026

🤖 Copilot Code Review — PR #113289

Holistic Assessment

Detailed Findings

✅ API Surface — Matches approved proposal exactly

✅ Source Generator Integration — Correct

✅ Implementation — JsonSeparatorNamingPolicy generalization

✅ Test Coverage — Comprehensive

💡 Suggestion — Class naming: JsonSeparatorNamingPolicy

💡 Suggestion — abstract vs sealed on JsonSeparatorNamingPolicy

✅ No behavioral changes to existing policies

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Ilchert commented Mar 1, 2026

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Copilot AI commented Feb 20, 2026 •

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stephentoub Mar 2, 2026 •

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✅ Implementation — `JsonSeparatorNamingPolicy` generalization

💡 Suggestion — Class naming: `JsonSeparatorNamingPolicy`

💡 Suggestion — `abstract` vs `sealed` on `JsonSeparatorNamingPolicy`

Ilchert commented Mar 1, 2026 •

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