Prefer string.AsSpan() over string.Substring() when parsing

[terrajobst]

The rule should flag instances of a pattern like int.Parse(str.Substring(...)) and instead switch to using the span-based int.Parse(str.AsSpan(...)). This would apply to all of the primitive types, and more generally potentially anything that has an overload taking a ReadOnlySpan<char> instead of a string.

Category: Performance

[jeffhandley]

Estimates:

• Analyzer: Small
• Fixer: Small

[GrabYourPitchforks]

Seems reasonable. We should figure out how much we want our analyzers (especially our on-by-default analyzers) to push people into using span. Using ROS<char> increases the concept count for scenarios which are currently very simple.

[bartonjs]

Video

• Find argument expressions that are str.Substring(...) and there's an overload (or the same overload) that accepts ReadOnlySpan<char> in that position
• Suggest changing Substring to AsSpan for the call

Category: Performance
Suggested severity: Info

[carlossanlop]

@Mrnikbobjeff also approved in case you already started working on this. Let us know if you'd like to get this issue assigned to you.

[Mrnikbobjeff]

@Mrnikbobjeff also approved in case you already started working on this. Let us know if you'd like to get this issue assigned to you.

I am currently working on porting my analyzers to be IOperation analyzers to be inline with the pattern already established. While I have a working implementation for a c# analyzer and fixer I still need to port the analyzer at least for this to be viable.

[carlossanlop]

Would you like me to assign this to you @Mrnikbobjeff or should i mark it up-for-grabs instead?

[carlossanlop]

I closed #33778 in favor of this one (it was an identical approved proposal).

Note to whoever decides to work on this: Please take a look at this comment in the dup issue, since it contains a list of cases this analyzer should be able to address.

[NewellClark]

I would like to be assigned to this. I'll start work on it immediately.

[AraHaan]

How does one enable this AsSpan diagnostics for netstandard2.0+ for using it over Substring?

Edit: It seems that the rule does not flag all uses of string.Substring, I would like all uses to get a diagnostic for replacing it with AsSpan as it will increase my program's performance indirectly, yes in some cases my code makes substrings and assigns them to variables before passing them to methods and so the AsSpan version could help me greatly in that case.