Avoid eagerly allocating in GetReferencedItemNamesAndMetadata

[Erarndt]

Slightly reduce allocations in GetReferencedItemNamesAndMetadata

Context

We can avoid eagerly creating a substring in this method to reduce allocations. The resulting "name" string is conditionally used in one place

                // If we've got this far, we know the item expression was
                // well formed, so make sure the name's in the table
                if ((whatToShredFor & ShredderOptions.ItemTypes) != 0)
                {
                    pair.Items ??= new HashSet<string>(MSBuildNameIgnoreCaseComparer.Default);
                    pair.Items.Add(name);
                }

We can capture the boundaries of the desired substring and only create it when we actually need it.

Before:

After:

Not a dramatic difference, but the change is small.

Changes Made

Testing

Notes

[Copilot]

Pull Request Overview

Defers string allocation in GetReferencedItemNamesAndMetadata by capturing name boundaries instead of creating substrings when scanning expressions.

• Updates the comment to reflect the boundary-capture approach.
• Introduces nameLength and defers the Substring call until inserting into pair.Items.

Comments suppressed due to low confidence (1)

src/Build/Evaluation/ExpressionShredder.cs:303

• [nitpick] Clarify the comment to reflect that substring creation is deferred until needed, e.g.: 'Determine name start and length, deferring substring creation until storage.'

// Grab the name boundaries, but continue to verify it's a well-formed expression