Optimize property expansion

[ladipro]

Fixes #6063

Context

Property expansion has been identified as one of the hot spots in project evaluation and ExpandPropertiesLeaveEscaped alone
accounts for almost 20% of overall evaluation time of simple projects.

Changes Made

Several optimizations have been made to the calltree under ExpandPropertiesLeaveEscaped. Notably:

• Unnecessary and counter-productive string pinning has been removed.
• A slow strchr-like function has been replaced with a simple call to String.IndexOf.
• Series of ifs have been replaced with a switch.
• Allocation of List<object> results has been eliminated.
• Allocation of temporary substrings extracted from the expression has been eliminated.

The combined performance win is 10% in ExpandPropertiesLeaveEscaped, so close to 2% for evaluation overall.

Testing

Expander is well covered by existing unit tests.

Notes

Please review commit by commit for easier to read diffs.

[donJoseLuis]

Cool stuff. The only thing to think about is if in a disposable type, you wish to check if instances have already been disposed prior to executing public method bodies.

[ladipro]

Thank you @donJoseLuis. I have addressed your feedback and updated the PR.

[Forgind]

I feel like there was a rumor of eventually replacing Expander entirely, but I might be misremembering.

[benvillalobos]

Looks great! Did you get a sense of how many properties were being expanded that only had a single object?

[ladipro]

I feel like there was a rumor of eventually replacing Expander entirely, but I might be misremembering.

That would be exciting (and scary at the same time). Any pointers to such plans would be welcome!

[Forgind]

I looked around, and what I found suggested no concrete plans—just an idea:
#5226 (comment)

I was probably a little premature here 🙂

[ladipro]

Looks great! Did you get a sense of how many properties were being expanded that only had a single object?

That's a great question. When building a .NET Core hello world console app, out of 5632 invocations of ExpandPropertiesLeaveTypedAndEscaped,

• 3002 don't expand any property (the string is a literal),
• 2261 expand to just one property (e.g. "$(Prop)"), out of which 52 expands to a non-string value,
• 122 expand to one property followed by a literal (e.g. "$(Prop)SomeString"),
• 22 expand to one property prepended by a literal (e.g. "SomeString$(Prop)"),
• 46 expand to one property followed and prepended by string literals (e.g. "Some$(Prop)String"),
• 182 expand multiple properties (e.g. "$(Prop)and$(AnotherProp)").

[donJoseLuis]

thanks for updating to check if instances are disposed in public members.