Publish the C# 9 alpha branch

[BillWagner]

Start the process of publishing the early alpha drafts in favor of the current committee working draft.

Fixes #52875

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📄 File	🔗 Preview link
docs/csharp/language-reference/builtin-types/enum.md	Enumeration types (C# reference)
docs/csharp/language-reference/compiler-messages/lambda-expression-errors.md	Errors and warnings when using lambda expressions and anonymous functions
docs/csharp/language-reference/compiler-messages/overloaded-operator-errors.md	Resolve errors and warnings related to operator declarations and overflow
docs/csharp/language-reference/keywords/const.md	The const keyword
docs/csharp/language-reference/operators/addition-operator.md	Addition operators - + and +=
docs/csharp/language-reference/operators/arithmetic-operators.md	Arithmetic operators (C# reference)
docs/csharp/language-reference/operators/assignment-operator.md	docs/csharp/language-reference/operators/assignment-operator
docs/csharp/language-reference/operators/bitwise-and-shift-operators.md	Bitwise and shift operators (C# reference)
docs/csharp/language-reference/operators/boolean-logical-operators.md	"Boolean logical operators - the boolean and, or, not, and xor operators"
docs/csharp/language-reference/operators/comparison-operators.md	Comparison operators (C# reference)
docs/csharp/language-reference/operators/conditional-operator.md	docs/csharp/language-reference/operators/conditional-operator
docs/csharp/language-reference/operators/delegate-operator.md	delegate operator
docs/csharp/language-reference/operators/equality-operators.md	Equality operators - test if two objects are equal or not
docs/csharp/language-reference/operators/is.md	"The is operator - Match an expression against a type or constant pattern"
docs/csharp/language-reference/operators/lambda-expressions.md	Lambda expressions and anonymous functions
docs/csharp/language-reference/operators/lambda-operator.md	docs/csharp/language-reference/operators/lambda-operator
docs/csharp/language-reference/operators/null-coalescing-operator.md	?? and ??= operators - the null-coalescing operators
docs/csharp/language-reference/operators/operator-overloading.md	"Operator overloading - Define unary, arithmetic, equality, and comparison operators."
docs/csharp/language-reference/operators/subtraction-operator.md	- and -= operators - subtraction (minus)
docs/csharp/language-reference/operators/switch-expression.md	docs/csharp/language-reference/operators/switch-expression
docs/csharp/language-reference/operators/true-false-operators.md	True and false operators
docs/csharp/language-reference/operators/type-testing-and-cast.md	Type-testing operators and cast expressions - is, as, typeof, and casts
docs/csharp/linq/index.md	Language Integrated Query (LINQ)
docs/csharp/specification/overview.md	C# standard specification
docs/csharp/specification/toc.yml	docs/csharp/specification/toc

[Copilot]

Pull request overview

This PR switches the published C# specification content from the current draft branch to an early C# 9 alpha draft, and updates multiple docs to point at the new section anchors in the specification.

Changes:

• Update the C# specification TOC and overview to present the C# 9 early draft.
• Revise many C# reference articles to link to updated section anchors in the spec.
• Adjust build/publishing configuration to pull the spec from the alpha-v9 branch and stop publishing C# 9 proposal pages.

Reviewed changes

Copilot reviewed 27 out of 27 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
docs/csharp/specification/toc.yml	Renames and restructures the specification TOC to target the C# 9 early draft and adds numbered chapter labels.
docs/csharp/specification/overview.md	Updates the overview text and date to describe the early C# 9 draft.
docs/csharp/linq/index.md	Updates the spec anchor for query expressions.
docs/csharp/language-reference/operators/type-testing-and-cast.md	Updates spec anchors for is and as.
docs/csharp/language-reference/operators/true-false-operators.md	Updates spec anchors for Boolean expressions and user-defined conditional logical operators.
docs/csharp/language-reference/operators/switch-expression.md	Updates the spec anchor for switch expressions.
docs/csharp/language-reference/operators/subtraction-operator.md	Updates spec anchors for delegate equality and subtraction operator sections.
docs/csharp/language-reference/operators/operator-overloading.md	Updates the spec anchor for user-defined conditional logical operators in the non-overloadable operator table.
docs/csharp/language-reference/operators/null-coalescing-operator.md	Updates spec anchors for null-coalescing and compound assignment sections.
docs/csharp/language-reference/operators/lambda-operator.md	Updates the spec anchor for anonymous function expressions.
docs/csharp/language-reference/operators/lambda-expressions.md	Updates the spec anchor for anonymous function expressions.
docs/csharp/language-reference/operators/is.md	Updates the spec anchor for the is operator section.
docs/csharp/language-reference/operators/equality-operators.md	Updates spec anchors for delegate equality and relational/type-testing operators.
docs/csharp/language-reference/operators/delegate-operator.md	Updates the spec anchor for anonymous function expressions.
docs/csharp/language-reference/operators/conditional-operator.md	Updates the spec anchor for the conditional operator section.
docs/csharp/language-reference/operators/comparison-operators.md	Updates spec anchor for relational and type-testing operators.
docs/csharp/language-reference/operators/boolean-logical-operators.md	Updates spec anchors for logical/conditional/compound assignment sections and user-defined conditional logical operators.
docs/csharp/language-reference/operators/bitwise-and-shift-operators.md	Updates spec anchors for shift/logical/compound assignment sections.
docs/csharp/language-reference/operators/assignment-operator.md	Updates spec anchor for assignment operators.
docs/csharp/language-reference/operators/arithmetic-operators.md	Updates spec anchors for remainder/multiplication/division/addition/subtraction/compound assignment sections.
docs/csharp/language-reference/operators/addition-operator.md	Updates spec anchor for addition operator section.
docs/csharp/language-reference/keywords/const.md	Updates spec anchor for constant expressions section.
docs/csharp/language-reference/compiler-messages/overloaded-operator-errors.md	Updates spec anchor for user-defined conditional logical operators.
docs/csharp/language-reference/compiler-messages/lambda-expression-errors.md	Updates spec anchors for anonymous function expressions references.
docs/csharp/language-reference/builtin-types/enum.md	Updates spec anchors for enum logical/comparison operators.
docfx.json	Updates doc build inputs/metadata, including removal of C# 9 proposal pages from the proposal doc set.
.openpublishing.publish.config.json	Switches the _csharpstandard source branch from draft-v8 to alpha-v9.

Comments suppressed due to low confidence (2)

docs/csharp/language-reference/operators/conditional-operator.md:89

• This page links to a C# 9 proposal doc (~/_csharplang/proposals/csharp-9.0/target-typed-conditional-expression.md). With this PR removing C# 9 proposal pages from the doc build, this link will likely break unless it’s updated to a different target (or the proposal pages stay published).

For more information, see the [Conditional operator](~/_csharpstandard/standard/expressions.md#1221-conditional-operator) section of the [C# language specification](~/_csharpstandard/standard/README.md).

Specifications for newer features are:

- [Target-typed conditional expression](~/_csharplang/proposals/csharp-9.0/target-typed-conditional-expression.md)

docs/csharp/language-reference/operators/lambda-expressions.md:336

• These feature proposal links point at C# 9 proposal docs under ~/_csharplang/proposals/csharp-9.0/…. Because this PR removes C# 9 proposal pages from the doc build, these links will likely break unless you update them to published targets (or restore publishing for C# 9 proposals).

For more information, see the [Anonymous function expressions](~/_csharpstandard/standard/expressions.md#1222-anonymous-function-expressions) section of the [C# language specification](~/_csharpstandard/standard/README.md).

For more information about these features, see the following feature proposal notes:

- [Lambda discard parameters](~/_csharplang/proposals/csharp-9.0/lambda-discard-parameters.md)
- [Static anonymous functions](~/_csharplang/proposals/csharp-9.0/static-anonymous-functions.md)
- [Lambda improvements](~/_csharplang/proposals/csharp-10.0/lambda-improvements.md)

[Copilot]

The link URL has a trailing space before the closing ), which can produce a broken link in Markdown. Remove the trailing space from the User-defined conditional logical operators link destination.

[Copilot]

The User-defined conditional logical operators link URL contains a trailing space before the closing ), which can break the link. Remove the trailing space from the link destination.

[Copilot]

The User-defined conditional logical operators link URL ends with a trailing space before ). Remove the trailing space to avoid a broken link.

[Copilot]

docfx.json no longer includes _csharplang/proposals/csharp-9.0/*.md in the published content, but multiple docs in the repo still link to those pages (for example, ~/_csharplang/proposals/csharp-9.0/records.md). Either keep publishing the C# 9 proposal pages, or update those references (and any redirects that target /dotnet/csharp/language-reference/proposals/csharp-9.0/...) so builds don’t ship broken links.

[Copilot]

This section links to the C# 9 records proposal (~/_csharplang/proposals/csharp-9.0/records.md). Since this PR stops publishing C# 9 proposal pages in docfx.json, this reference will likely become a broken link unless it’s updated to a published target (or the proposal pages remain included).