Preserve encoding and trailing newlines in dotnet-tools.json

[Thomas-Shephard]

dotnet tool commands (install, update, uninstall) perform an invasive rewrite of the dotnet-tools.json manifest that disregards original file formatting and encoding.

Changes

• Updated ToolManifestEditor to be format-aware by capturing encoding and newline status during the read phase.
• Replaced JsonDocument.Parse(stream) with StreamReader and JsonDocument.Parse(text) to support BOM detection and UTF-16.
• Added a Write helper to restore formatting during manifest updates.
• Added verification tests in ToolManifestEditorTests.

Fixes #53045

[Copilot]

Pull request overview

This PR aims to make dotnet tool manifest edits non-invasive by preserving the original dotnet-tools.json file encoding (including BOM) and whether it ends with a trailing newline, while also fixing failures when reading UTF-16 manifests.

Changes:

• Update ToolManifestEditor to capture original encoding + trailing-newline state on read and reuse it on write.
• Switch JSON parsing from JsonDocument.Parse(stream) to BOM-aware StreamReader + JsonDocument.Parse(text) to support UTF-16.
• Add tests asserting BOM + trailing newline preservation for UTF-8 BOM and UTF-16 LE manifests.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Cli/dotnet/ToolManifest/ToolManifestEditor.cs	Captures encoding/newline metadata during read and uses it when writing updated manifests.
test/dotnet.Tests/ToolManifestTests/ToolManifestEditorTests.cs	Adds verification coverage for BOM + trailing newline preservation during manifest updates.

Comments suppressed due to low confidence (1)

src/Cli/dotnet/ToolManifest/ToolManifestEditor.cs:166

• DeserializeLocalToolsManifest has mismatched/mis-indented braces around the using (JsonDocument doc = JsonDocument.Parse(text)) block (and the subsequent if statements). As written, the using block is never closed and several if blocks are not correctly scoped/indented, which should cause a compilation error and/or incorrect parsing flow. Please fix the brace structure so all root.TryGet* parsing happens inside the JsonDocument using block, and ensure both the JsonDocument and StreamReader scopes are properly closed.

                using (JsonDocument doc = JsonDocument.Parse(text))
                {
                    JsonElement root = doc.RootElement;

                    if (root.TryGetInt32Value(JsonPropertyVersion, out var version))
                {
                    serializableLocalToolsManifest.Version = version;
                }

                if (root.TryGetBooleanValue(JsonPropertyIsRoot, out var isRoot))

[Thomas-Shephard]

@martincostello is there anything else I need to get this actually merged?

[martincostello]

Wait for someone on the team to review it and merge it - there's nothing I can do.

[Thomas-Shephard]

Ah, must have got confused - thought you were part of the dotnet org.

@dotnet-cli

[martincostello]

I am, but I'm not a member of the .NET team or an MS employee.