Add methods from #27912 (Flow System.Text.Rune through more APIs)

[Joy-less]

Supercedes #111815.

This time the methods are fully implemented and ready to go, and the ref assemblies are added to match the implementations.

[Copilot]

Pull Request Overview

This PR adds a set of new API overloads to support System.Text.Rune across various string and text manipulation APIs, addressing methods such as Equals, Contains, IndexOf/LastIndexOf, Replace, Trim, Append, Insert, and Write. The changes span multiple libraries including System.Runtime and System.Private.CoreLib to fully integrate rune-based operations.

• Added overloads for string comparison methods accepting System.Text.Rune.
• Introduced new methods on StringBuilder, TextWriter, and TextInfo to handle rune conversion and manipulation.
• Updated internal string splitting and trimming routines to support rune separators and trim characters.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Runtime/ref/System.Runtime.cs	Added new overloads for string API methods accepting System.Text.Rune and StringComparison.
src/libraries/System.Private.CoreLib/src/System/Text/StringBuilder.cs	Added Append/Insert/Replace methods with System.Text.Rune and Rune retrieval overloads.
src/libraries/System.Private.CoreLib/src/System/Text/Rune.cs	Updated Equals implementations and added new overloads for comparing Runes with StringComparison.
src/libraries/System.Private.CoreLib/src/System/String.Searching.cs	Provided new overloads of Contains, IndexOf, and LastIndexOf for System.Text.Rune with careful iteration over surrogates.
src/libraries/System.Private.CoreLib/src/System/String.Manipulation.cs	Added Replace, Split, and Trim overloads using System.Text.Rune for enhanced string manipulation.
src/libraries/System.Private.CoreLib/src/System/String.Comparison.cs	Extended StartsWith and EndsWith to support System.Text.Rune comparisons.
src/libraries/System.Private.CoreLib/src/System/IO/TextWriter.cs	Integrated Write and WriteLine overloads that accept System.Text.Rune.
src/libraries/System.Private.CoreLib/src/System/Globalization/TextInfo.cs	Implemented ToLower and ToUpper for System.Text.Rune conversions.
src/libraries/System.Private.CoreLib/src/System/Char.cs	Added an overload for Equals accepting a StringComparison using modern array initialization.

Comments suppressed due to low confidence (1)

src/libraries/System.Private.CoreLib/src/System/Text/StringBuilder.cs:2850

• In GetRuneAt(int index), consider throwing a more specific exception type (such as ArgumentOutOfRangeException) rather than a generic Exception for improved clarity and consistency with API design.

            throw new Exception($"Unable to get rune at {index}.");

[jeffhandley]

@stephentoub - Since this has been open as long as it has, I wanted to check with you that we should still pursue adding the Rune overloads. Any concerns or hesitations?

[Joy-less]

@jeffhandley I have made some changes to my PR:

• Fixed TextInfo.ToLower(Rune) and TextInfo.ToUpper(Rune) for runes which use two chars. Very niche but affects some characters like 𐐨 (\uD801\uDC28) -> 𐐀 (\uD801\uDC00).
• Used the ordinal char.Equals(char) implementation for char.Equals(char, StringComparison) when StringComparison is StringComparison.Ordinal.

I think #111170 is a relevant pull request to this one.

Also, the original creator of the API proposals for both this pull request and the above pull request has this on their profile:

On other projects, not checking GitHub notifications - ping via Teams if urgent.

[tarekgh]

@Joy-less I'll get into this PR in the next few days. Thanks!

[Joy-less]

@Joy-less I'll get into this PR in the next few days. Thanks!

@tarekgh Any update?

[tarekgh]

Looks I accidentality merged with unrealted main changes. I'll try to fix that.

[tarekgh]

Thanks, @Joy-less, for all your effort in making this change.

[jkotas]

This change introduced failing tests that are causing many legs to fail on all PRs now. I am submitting a revert (unless these failures get fixed quickly). Example of a failure #120137 , but there may be more.

Build analysis have not flagged these failures for some reason.

[Joy-less]

This change introduced failing tests that are causing many legs to fail on all PRs now. I am submitting a revert (unless these failures get fixed quickly). Example of a failure #120137 , but there may be more.

Build analysis have not flagged these failures for some reason.

I see the issue with that failing test, it's doing reflection to check that all methods are overridden on the NullTextWriter. I can create a pull request ASAP to fix that failing test if that's the only one.

Edit: Please see #120145.