Improve invalid feature name reporting

[BillyONeal]

When a feature name is invalid, report the error as part of the feature name rather than as part of the overall features block.

Before and after demonstration:

PS C:\Dev\vcpkg-tool\out\build\Win-x64-Debug-WithArtifacts> type C:\Dev\vcpkg-tool\azure-pipelines\e2e-ports\vcpkg-requires-feature\vcpkg.json
{
  "name": "vcpkg-requires-feature",
  "version": "0",
  "features": {
    "a": {
      "description": "Feature A"
    },
    "b": {
      "description": "Feature B"
    },
    "b_required": {
      "description": "This feature needs to be turned on for the port to build"
    },
    "c": {
      "description": "Feature C"
    }
  }
}
PS C:\Dev\vcpkg-tool\out\build\Win-x64-Debug-WithArtifacts> C:\Dev\vcpkg\vcpkg.exe format-manifest C:\Dev\vcpkg-tool\azure-pipelines\e2e-ports\vcpkg-requires-feature\vcpkg.json
C:\Dev\vcpkg-tool\azure-pipelines\e2e-ports\vcpkg-requires-feature\vcpkg.json: error: $.features (a set of features): features must be lowercase alphanumeric+hyphens, and not one of the reserved names
PS C:\Dev\vcpkg-tool\out\build\Win-x64-Debug-WithArtifacts> .\vcpkg.exe format-manifest C:\Dev\vcpkg-tool\azure-pipelines\e2e-ports\vcpkg-requires-feature\vcpkg.json
C:\Dev\vcpkg-tool\azure-pipelines\e2e-ports\vcpkg-requires-feature\vcpkg.json: error: $.features.b_required (a feature): features must be lowercase alphanumeric+hyphens, and not one of the reserved names
PS C:\Dev\vcpkg-tool\out\build\Win-x64-Debug-WithArtifacts>

[Copilot]

Pull Request Overview

This PR refactors how invalid feature names are reported, ensuring that error messages are associated with the specific feature rather than the overall features block.

• Changed error reporting in feature parsing to use a field-level error handler instead of a generic error.
• Introduced a new function add_field_name_error in both the JSON reader implementation and header.
• Updated end-to-end tests to verify the new error reporting message format.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/vcpkg/sourceparagraph.cpp	Replaces generic error reporting with field-specific error reporting for invalid feature names.
src/vcpkg/base/json.cpp	Adds a new add_field_name_error method that wraps generic error reporting with additional context.
include/vcpkg/base/jsonreader.h	Declares the new add_field_name_error method.
azure-pipelines/end-to-end-tests-dir/format-manifest.ps1	Updates test expectations to reflect the new error message format.
azure-pipelines/e2e-assets/format-manifest-malformed/bad-feature-name.json	Provides a sample manifest to trigger the new error reporting.

Comments suppressed due to low confidence (2)

azure-pipelines/end-to-end-tests-dir/format-manifest.ps1:21

• [nitpick] Ensure that this test case remains valid if the error message wording is refined further in future updates, as it specifically checks the new field-level error message format.

$output = Run-VcpkgAndCaptureOutput @commonArgs format-manifest "$PSScriptRoot/../e2e-assets/format-manifest-malformed/bad-feature-name.json"

src/vcpkg/sourceparagraph.cpp:1111

• This change improves error reporting by tying the error specifically to the feature name. Verify that the new error message format fully meets the documented requirements for invalid feature names.

r.add_field_name_error(

[Copilot]

[nitpick] Consider adding inline documentation here to explain that add_field_name_error wraps the generic error logic while providing additional context from the field name.

Suggested change

	// This function wraps add_generic_error while temporarily appending the field name to the path.
	// It provides additional context by including the field name in the error message.

[Copilot]

[nitpick] It would be beneficial to add a comment describing the purpose of add_field_name_error and how it differs from add_generic_error.

Suggested change

	void add_extra_field_error(const LocalizedString& type, StringView fields, StringView suggestion = {});
	void add_generic_error(const LocalizedString& type, StringView message);
	void add_extra_field_error(const LocalizedString& type, StringView fields, StringView suggestion = {});
	// Reports a general error related to the JSON object, not tied to a specific field.
	void add_generic_error(const LocalizedString& type, StringView message);
	// Reports an error related to a specific field name in the JSON object.
	// Use this method when the error pertains to a particular field, such as a missing or invalid value.