Add C# 14 error message before extensions

Author: BillWagner

docs/csharp/language-reference/compiler-messages/partial-declarations.md

@@ -49,6 +49,13 @@ f1_keywords:
   - "CS9263"
   - "CS9264"
   - "CS9266"
+  - "CS9273"
+  - "CS9275"
+  - "CS9276"
+  - "CS9277"
+  - "CS9278"
+  - "CS9279"
+  - "CS9280"
 helpviewer_keywords:
   - "CS0260"
   - "CS0261"
@@ -96,7 +103,14 @@ helpviewer_keywords:
   - "CS9258"
   - "CS9263"
   - "CS9266"
-ms.date: 11/06/2024
+  - "CS9273"
+  - "CS9275"
+  - "CS9276"
+  - "CS9277"
+  - "CS9278"
+  - "CS9279"
+  - "CS9280"
+ms.date: 05/23/2025
 ---
 # Errors and warnings related to `partial` type and `partial` member declarations
 
@@ -150,11 +164,18 @@ That's by design. The text closely matches the text of the compiler error / warn
 - [**CS9257**](#partial-properties): *Both partial property declarations must be required or neither may be required*
 - [**CS9258**](#field-backed-properties): *In this language version, the '`field`' keyword binds to a synthesized backing field for the property. To avoid generating a synthesized backing field, and to refer to the existing member, use '`this.field`' or '`@field`' instead.*
 - [**CS9263**](#field-backed-properties): *A partial property cannot have an initializer on both the definition and implementation.*
+- [**CS9275**](#partial-members): *Partial member  must have an implementation part.*
+- [**CS9276**](#partial-members): *Partial member  must have a definition part.*
+- [**CS9277**](#partial-members): *Partial member may not have multiple defining declarations.*
+- [**CS9278**](#partial-members): *Partial member may not have multiple implementing declarations.*
+- [**CS9279**](#partial-events-and-constructors): *Partial event cannot have initializer.*
+- [**CS9280**](#partial-events-and-constructors): *Only the implementing declaration of a partial constructor can have an initializer.*
 
 The following warnings can be generated for field backed properties:
 
 - [**CS9264**](#field-backed-properties): *Non-nullable property must contain a non-null value when exiting constructor. Consider adding the 'required' modifier, or declaring the property as nullable, or adding '`[field: MaybeNull, AllowNull]`' attributes.**
 - [**CS9266**](#field-backed-properties): *One accessor of property  should use '`field`' because the other accessor is using it.*
+- [**CS9273**](#field-backed-properties): *In this language version, '`field`' is a keyword within a property accessor. Rename the variable or use the identifier '`@field`' instead.*
 
 The following sections explain the cause and fixes for these errors and warnings.
 
@@ -202,8 +223,12 @@ The compiler warns you if you have multiple fields declared in multiple files fo
 - **CS8800**: *Both partial member declarations must have identical combinations of `virtual`, `override`, `sealed`, and `new` modifiers.*
 - **CS8818**: *Partial member declarations must have matching `ref` return values.*
 - **CS8988**: *The `scoped` modifier of parameter doesn't match partial definition.*
+- **CS9275**: *Partial member  must have an implementation part.*
+- **CS9276**: *Partial member  must have a definition part.*
+- **CS9277**: *Partial member may not have multiple defining declarations.*
+- **CS9278**: *Partial member may not have multiple implementing declarations.*
 
-Partial members have two declarations. The declaration without an implementation is the *declaring declaration*. The declaration with the implementation is the *implementing declaration*. Partial members are allowed only in a `partial` type. Partial members can't be `abstract`. Partial members can't explicitly implement an interface. Both declarations of a partial member must have identical signatures. For example, either both or neither declarations can include the `static` or `unsafe` modifiers.
+Partial members must have two declarations. The declaration without an implementation is the *defining declaration*. The declaration with the implementation is the *implementing declaration*. Both declarations are required. Partial members are allowed only in a `partial` type. Partial members can't be `abstract`. Partial members can't explicitly implement an interface. Both declarations of a partial member must have identical signatures. For example, either both or neither declarations can include the `static` or `unsafe` modifiers.
 
 ## Partial methods
 
@@ -249,15 +274,23 @@ A partial property or indexer must have both a *declaring declaration* and an *i
 public partial int ImplementingDeclaration { get => field; set; }
 ```
 
+## Partial events and constructors
+
+- **CS9279**: *Partial event cannot have initializer.*
+- **CS9280**: *Only the implementing declaration of a partial constructor can have an initializer.*
+
+You've declared an initializer on the defining declaration of a partial constructor or on a partial event declaration. You must remove it.
+
 ## field backed properties
 
 - **CS9258**: *In this language version, the '`field`' keyword binds to a synthesized backing field for the property. To avoid generating a synthesized backing field, and to refer to the existing member, use '`this.field`' or '`@field`' instead.*
 - **CS9263**: *A partial property cannot have an initializer on both the definition and implementation.*
 - **CS9264**: *Non-nullable property must contain a non-null value when exiting constructor. Consider adding the 'required' modifier, or declaring the property as nullable, or adding '`[field: MaybeNull, AllowNull]`' attributes.**
 - **CS9266**: *One accessor of property  should use '`field`' because the other accessor is using it.*
+- **CS9273**: *In this language version, '`field`' is a keyword within a property accessor. Rename the variable or use the identifier '`@field`' instead.*
 
 [!INCLUDE[field-preview](../../includes/field-preview.md)]
 
-Beginning with C# 13, the preview feature, `field` backed properties allows you to access the compiler synthesized backing field for a property. **CS9258** indicates that you have a variable named `field`, which can be hidden by the contextual keyword `field`.
+Beginning with C# 13, the preview feature, `field` backed properties allows you to access the compiler synthesized backing field for a property. **CS9258** or **CS9273** indicate that you have a variable named `field`, which can be hidden by the contextual keyword `field`.
 
 **CS9263** indicates that your declaring declaration includes an implementation. That implementation might be accessing the compiler synthesized backing field for that property. **CS9264** indicates that the your use of `field` assumes a non-nullable backing field while the property declaration is nullable. The compiler assumes both the backing field and the property have the same nullability. You need to add the `[field:MaybeNull, AllowNull]` attribute to the property declaration to indicate that the `field` value should be considered nullable. **CS9266** indicates that one of a properties accessors uses the `field` keyword, but the other uses a hand-declared backing field. The warning indicates you may have done that by accident.

docs/csharp/language-reference/compiler-messages/string-literal.md

@@ -0,0 +1,23 @@
+---
+title: Errors and warnings for string literal declarations
+description: This article helps you diagnose and correct compiler errors and warnings when you declare string literals as constants or variables.
+f1_keywords:
+  - "CS9274"
+helpviewer_keywords:
+  - "CS9274"
+ms.date: 05/23/2025
+---
+# Errors and warnings for string literal declarations
+
+There are a few *errors* related to declaring string constants or string literals.
+
+<!-- The text in this list generates issues for Acrolinx, because they don't use contractions.
+That's by design. The text closely matches the text of the compiler error / warning for SEO purposes.
+ -->
+- [**CS9274**](#constant-declarations): *Cannot emit this string literal into the data section because it has XXHash128 collision with another string literal.*
+
+## Constant declarations
+
+- [**CS9274**](#constant-declarations): *Cannot emit this string literal into the data section because it has XXHash128 collision with another string literal.*
+
+These errors indicate that your declaration can't be emitted in the data section. Turn this feature off for your application.

docs/csharp/language-reference/toc.yml

@@ -466,7 +466,7 @@ items:
       CS0171, CS0188, CS0843, CS8904, CS1738, CS8022, CS8023, CS8024, CS8025, CS8026, CS8058, CS8059, CS8107, CS8192, CS8302,
       CS8303, CS8304, CS8305, CS8306, CS8314, CS8320, CS8370, CS8371, CS8400, CS8401, CS8511, CS8627, CS8630, CS8652, CS8703,
       CS8704, CS8706, CS8773, CS8912, CS8919, CS8929, CS8936, CS8957, CS8967, CS9014, CS9015, CS9016, CS9017, CS9058, CS9064,
-      CS9103, CS9171, CS9194, CS9202, CS9204, CS9240, CS9260, CS9268, CS9269
+      CS9103, CS9171, CS9194, CS9202, CS9204, CS9240, CS9260, CS9268, CS9269, CS9271
   - name: Assembly references
     href: ./compiler-messages/assembly-references.md
     displayName: >
@@ -503,18 +503,22 @@ items:
     displayName: >
       yield return, yield break,
       CS1622, CS1624, CS1625, CS1626, CS1627, CS1629, CS1631, CS1637, CS4013, CS8154, CS8176, CS9237, CS9238, CS9239
+  - name: Extension declarations
+    href: ./compiler-messages/extension-declarations.md
+    displayName: 
   - name: Partial declarations
     href: ./compiler-messages/partial-declarations.md
     displayName: >
       partial type, partial member, partial method, partial property, partial indexer,
       CS0260, CS0261, CS0262, CS0263, CS0264, CS0265, CS0267, CS0282, CS0501, CS0750, CS0751, CS0754, CS0755, CS0756, CS0757,
       CS0759, CS0761, CS0762, CS0763, CS0764, CS1067, CS8142, CS8663, CS8795, CS8796, CS8797, CS8798, CS8799, CS8800, CS8817,
       CS8818, CS8863, CS8988, CS9248, CS9249, CS9250, CS9251, CS9252, CS9253, CS9254, CS9255, CS9256, CS9257, CS9258, CS9263,
-      CS9264, CS9266
+      CS9264, CS9266, CS9273, CS9275, CS9276, CS9277, CS9278, CS9279, CS9280
   - name: Params modifier
     href: ./compiler-messages/params-arrays.md
     displayName: >
-      CS0225, CS0231, CS0466, CS0674, CS0758, CS1104, CS1611, CS1670, CS1751, CS9218, CS9223, CS9224, CS9225, CS9227, CS9228
+      CS0225, CS0231, CS0466, CS0674, CS0758, CS1104, CS1611, CS1670, CS1751, CS9218, CS9223, CS9224, CS9225, CS9227, CS9228,
+      CS9272
   - name: Nullable warnings
     href: ./compiler-messages/nullable-warnings.md
     displayName: >
@@ -525,6 +529,9 @@ items:
   - name: Pattern matching warnings
     href: ./compiler-messages/pattern-matching-warnings.md
     displayName: CS8509, CS9134, CS9135
+  - name: String literal declarations
+    href: ./compiler-messages/string-literal-errors.md
+    displayName: CS9274
   - name: Array declarations
     href: ./compiler-messages/array-declaration-errors.md
     displayName: >

docs/csharp/misc/sorry-we-don-t-have-specifics-on-this-csharp-error.md

@@ -622,14 +622,6 @@ f1_keywords:
   - "CS9235"
   - "CS9236"
 # C# 14 errors begin here
-  - "CS9273"
-  - "CS9274"
-  - "CS9275"
-  - "CS9276"
-  - "CS9277"
-  - "CS9278"
-  - "CS9279"
-  - "CS9280"
   - "CS9281"
   - "CS9282"
   - "CS9283"