System.Text.Json conversion for template engine project and tests

[NikolaMilosavljevic]

Newtonsoft.Json → System.Text.Json Migration: Microsoft.TemplateEngine.Cli

Overview

Migrated src/Cli/Microsoft.TemplateEngine.Cli from Newtonsoft.Json (JObject, JToken, JArray, etc.) to System.Text.Json (JsonNode, JsonObject, JsonArray, JsonValue). The project has <IsAotCompatible>true</IsAotCompatible>, so all serialization avoids reflection-based APIs.

Files Changed

Source (8 files)

File	Key Changes
JExtensions.cs	Full rewrite. ReadObject() returns JsonObject, WriteObject() uses Utf8JsonWriter. TryParse() returns JsonNode?. Added GetPropertyCaseInsensitive() helper.
AliasModel.cs	[JsonProperty] → [JsonInclude] on public properties.
AliasRegistry.cs	Save() builds JsonObject/JsonArray manually (AOT-safe). ToStringListDictionary() uses case-insensitive property lookup matching original Newtonsoft behavior.
HostSpecificTemplateData.cs	Constructor takes JsonObject?. Boolean values handled via JsonValueKind.True/False switch. Custom JsonConverter rewritten with Utf8JsonWriter. UsageExamples parsing filters by JsonValueKind.String before calling GetValue<string>().
HostSpecificDataLoader.cs	JObject.Parse → JsonNode.Parse()?.AsObject(). Both string and stream parse paths use JsonDocumentOptions with CommentHandling = Skip and AllowTrailingCommas = true.
CliHostSearchCacheData.cs	JObject → JsonObject. Property detection uses HashSet<string> with OrdinalIgnoreCase for O(1) lookup instead of nested LINQ.
ChmodPostActionProcessor.cs	JArray.Parse → JsonNode.Parse().AsArray().
PostActionProcessorBase.cs	Token type checks use JsonValueKind enum.

Tests (3 files)

File	Key Changes
AliasAssignmentTests.cs	JObject.Parse → JsonNode.Parse. Typed GetValue<string>()/GetValue<bool>() for value extraction.
HostDataLoaderTests.cs	JObject.FromObject → JsonSerializer.SerializeToNode. Property assertions rewritten for JsonObject.
TemplateSearchCoordinatorTests.cs	JObject.FromObject(cache).ToString() → JsonSerializer.Serialize(cache).

Notable Design Decisions

1. No JsonSerializer.Serialize<T>() in production code — all serialization uses Utf8JsonWriter manual writes or JsonNode.WriteTo() to remain AOT-compatible.

2. JsonArray.Add((JsonNode)JsonValue.Create(item)!) pattern — generic Add<T> triggers AOT warnings; explicit cast avoids them.

3. Case-insensitive property access — Newtonsoft property access was case-insensitive by default. STJ's JsonObject is case-sensitive, so GetPropertyCaseInsensitive() helpers and manual iteration were added where backward compatibility matters (e.g., AliasRegistry.ToStringListDictionary, HostSpecificTemplateData constructor).

4. JsonDocumentOptions for lenient parsing — HostSpecificDataLoader and JExtensions.TryParse() explicitly opt into comment skipping and trailing commas, matching the permissive parsing behavior of Newtonsoft's defaults.

5. Defensive value extraction — UsageExamples filters elements by JsonValueKind.String before calling GetValue<string>() to avoid InvalidOperationException on unexpected element types.

6. O(1) property detection — CliHostSearchCacheData builds a HashSet<string>(StringComparer.OrdinalIgnoreCase) from cache keys once, replacing a nested O(n×m) LINQ query.

Verification

• Build: 0 errors, 0 warnings (AOT-compatible)
• Tests: 773 passed, 0 failed, 6 skipped (pre-existing skips)

[Copilot]

Pull request overview

Migrates Microsoft.TemplateEngine.Cli and its unit tests off the transitive Newtonsoft.Json dependency and onto System.Text.Json, including replacing JObject/JToken usage with JsonNode/JsonObject and updating serialization/deserialization paths to be AOT-safe.

Changes:

• Rewrote CLI JSON helper extensions (JExtensions) for System.Text.Json.Nodes and updated consumers.
• Updated host-specific template data loading/serialization and CLI host cache parsing to use STJ nodes.
• Updated alias persistence and unit tests to use STJ serialization APIs.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
test/Microsoft.TemplateEngine.Cli.UnitTests/TemplateSearchCoordinatorTests.cs	Switches cache JSON creation from JObject.FromObject to JsonSerializer.Serialize.
test/Microsoft.TemplateEngine.Cli.UnitTests/HostDataLoaderTests.cs	Updates serialization/assertions to use JsonSerializer.SerializeToNode and JsonObject APIs.
test/Microsoft.TemplateEngine.Cli.UnitTests/AliasAssignmentTests.cs	Moves test parsing/assertions from JObject/JValue to JsonNode + typed GetValue<T>().
src/Cli/Microsoft.TemplateEngine.Cli/TemplateSearch/CliHostSearchCacheData.cs	Ports cache additional-data reader from JObject to JsonObject.
src/Cli/Microsoft.TemplateEngine.Cli/PostActionProcessors/PostActionProcessorBase.cs	Ports JSON parsing for targetFiles from JToken/JArray to JsonNode/JsonArray.
src/Cli/Microsoft.TemplateEngine.Cli/PostActionProcessors/ChmodPostActionProcessor.cs	Ports chmod args parsing from JArray.Parse to JsonNode.Parse().AsArray().
src/Cli/Microsoft.TemplateEngine.Cli/JExtensions.cs	Replaces Newtonsoft-based helper extensions with System.Text.Json node-based helpers and file read/write.
src/Cli/Microsoft.TemplateEngine.Cli/HostSpecificTemplateData.cs	Ports host data model parsing and custom converter to System.Text.Json and AOT-safe writing.
src/Cli/Microsoft.TemplateEngine.Cli/HostSpecificDataLoader.cs	Switches host JSON reading from JsonTextReader/JObject.Load to JsonNode.Parse.
src/Cli/Microsoft.TemplateEngine.Cli/Alias/AliasRegistry.cs	Updates alias file read/write to use JsonObject and writes JSON via JExtensions.WriteObject.
src/Cli/Microsoft.TemplateEngine.Cli/Alias/AliasModel.cs	Replaces [JsonProperty] with [JsonInclude] (STJ attribute).

[NikolaMilosavljevic]

Failures are unrelated and known issues.