Dev/erarndt/project root element

[Erarndt]

Fixes #

Context

To combat expensive individual garbage collections, it's important to minimize the amount of memory that gets promoted. One way to help is to shrink the size of the objects. This PR trims ProjectRootElement. This is a heap snapshot when building OrchardCore.

There are roughly 13.7MB of these items on the heap (~66k at 206B per object).

The _escapedFullPath is intended to cache the result for the EscapedFullPath property. However, this is called very infrequently (I saw once per build), so the field provides little value.

There are two fields, _dirtyReason and _dirtyParameter that are only used when the MSBUILDDEBUGEVALUATION environment variable is set. I believe we can remove these fields and still provide useful information by updating the trace messages.

The IsEphemeral property is rarely used, and it can be covered by having another class that includes this field (EphemeralProjectRootElement) and used in places where an ephemeral version is needed.

Finally, ContainsTargetsWithReturnsAttribute was only ever written to, so it can be removed.

Changes Made

Testing

Notes

[Copilot]

Pull Request Overview

This PR optimizes memory usage by trimming the ProjectRootElement class to reduce object size from 206B per instance, addressing garbage collection performance issues. The optimization targets ~66k objects consuming 13.7MB during OrchardCore builds.

• Removes rarely-used cached fields and debug-only properties
• Replaces boolean IsEphemeral property with type-based approach using EphemeralProjectRootElement subclass
• Eliminates unused ContainsTargetsWithReturnsAttribute field

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/Build/Construction/ProjectRootElement.cs	Main optimization removing cached fields, debug properties, and introducing EphemeralProjectRootElement subclass
src/Build/Construction/ProjectTargetElement.cs	Removes code that set the now-deleted ContainsTargetsWithReturnsAttribute field
src/Build/Definition/Project.cs	Updates to use type checking instead of IsEphemeral property and simplifies debug trace messages

[AR-May]

Let's run exp insertion for this PR.

[SimaTian]

Hello, according to my search in code, there are several possible dirty reasons.
Are we reasonably sure that they are not in use please?

	MarkDirty("Set project FullPath to '{0}'", FullPath);	D:\bld\src\Build\Construction\ProjectRootElement.cs	456	17	Microsoft.Build	FullPath	ProjectRootElement	Read	
	MarkDirty("Project reloaded", null);	D:\bld\src\Build\Construction\ProjectRootElement.cs	1732	13	Microsoft.Build	ReloadFrom	ProjectRootElement	Read	
	MarkDirty("Set express as attribute: {0}", value.ToString());	D:\bld\src\Build\Construction\ProjectElement.cs	92	21	Microsoft.Build	ExpressedAsAttribute	ProjectElement	Read	
	MarkDirty("CopyFrom", null);	D:\bld\src\Build\Construction\ProjectElement.cs	415	13	Microsoft.Build	CopyFrom	ProjectElement	Read	
	MarkDirty("Replace element {0}", newElement.Name);	D:\bld\src\Build\Construction\ProjectElement.cs	467	13	Microsoft.Build	ReplaceElement	ProjectElement	Read	

Or maybe (to be on a safer side) since there is a limited pool of the reasons, we could shift to an enum to keep the information while getting rid of the string.