Add support for target typed conditional expression

.github/ISSUE_TEMPLATE/docs-feedback.yml

@@ -0,0 +1,46 @@
+name: Learn feedback control.
+description: |
+  ⛔ This template is hooked into the feedback control on the bottom of every page on the learn.microsoft.com site. It automatically fills in several fields for you. Don't use for other purposes. ⛔
+body:
+  - type: markdown
+    attributes:
+      value: "## Issue information"
+  - type: markdown
+    attributes:
+      value: Select the issue type, and describe the issue in the text box below. Add as much detail as needed to help us resolve the issue. Make sure to include the relevant section number. The committee is working on C# 8 currently. Don't write issues about features added after that version.
+  - type: dropdown
+    id: issue-type
+    attributes:
+      label: Type of issue
+      options:
+        - Typo
+        - Spec incorrect
+        - Spec incomplete
+        - xref missing
+        - Other (describe below)
+    validations:
+      required: true
+  - type: textarea
+    id: feedback
+    validations:
+      required: true
+    attributes:
+      label: Description
+  - type: markdown
+    attributes:
+      value: "## 🚧 Document information 🚧"
+  - type: markdown
+    attributes:
+      value: "*Don't modify the following fields*. They are automatically filled in for you. Doing so will disconnect your issue from the affected article. *Don't edit them*."
+  - type: input
+    id: pageUrl
+    validations:
+      required: true
+    attributes:
+      label: Page URL
+  - type: input
+    id: contentSourceUrl
+    validations:
+      required: true
+    attributes:
+      label: Content source URL

.github/dependabot.yml

@@ -0,0 +1,19 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions" # Core GitHub Actions
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "wednesday"
+    open-pull-requests-limit: 10
+  - package-ecosystem: "nuget"
+    directory: "/tools" #tools.sln
+    schedule:
+      interval: "weekly"
+      day: "wednesday"
+    open-pull-requests-limit: 5
+    groups:
+      # Group .NET updates together for solutions.
+      dotnet:
+        patterns:
+          - "*" # Prefer a single PR per solution update.

.github/workflows/dependencies/ReplaceAndAdd.md

@@ -32,88 +32,15 @@ the automatic section numbering tooling, they **must** be maintained manually.
 
 # Verification-Only Replacements & Additions
 
-This set of replacements and additions is the bare minimum required to allow the grammar to verify and run, though
-it may not produce the desired parse (that requires at least the use of modes and/or
-lexical predicates).
+This set of replacements and additions is the bare minimum required to allow the grammar
+to verify and run, though it may not produce the desired lex and parse (that requires at
+least the use of modes and/or lexical predicates).
 
-This set can be used as a basic check that the grammar is a correct ANTLR grammar.
+Pre-processing directives are skipped like whitespace, however lexing confirms the lexical
+grammar is valid.
 
----
-
-## Top Level Rule
-
-The Standard’s *compilation_unit* as is will allow garbage at the end of a file, this
-rule has an EOF requirement to ensure the whole of the input must be a correct program.
-
-> *Note: The section number makes this the first rule in the grammar, not required but it
-has to go somewhere…*
-
-### 0.0.0 Top Level Rule
-
-```ANTLR
-// [ADDED] Rule added as the start point
-prog: compilation_unit EOF;
-```
----
-
-## Discarding Whitespace
-
-The following changes in §7.3.2, §7.3.3 and §7.3.4, add `-> skip` to the “whitespace”
-token rules so that are not passed to the parser. This behaviour is implicit in the
-Standard.
-
-### 7.3.2 Line terminators
-
-```ANTLR
-// [SKIP]
-New_Line
-    : ( New_Line_Character
-      | '\u000D\u000A'    // carriage return, line feed 
-      ) -> skip
-    ;
-```
-
-### 7.3.3 Comments
-
-```ANTLR
-// [SKIP]
-Comment
-    : ( Single_Line_Comment
-      | Delimited_Comment
-      ) -> skip
-    ;
-```
-
-### 7.3.4 White space
-
-```ANTLR
-// [SKIP]
-Whitespace
-    : ( [\p{Zs}]  // any character with Unicode class Zs
-      | '\u0009'  // horizontal tab
-      | '\u000B'  // vertical tab
-      | '\u000C'  // form feed
-      ) -> skip
-    ;
-
-```
-
----
-
-## Pre-processing directives
-
-This change causes all pre-processor directives to be discarded, they don’t need to be
-processed to validate the grammar (processing them would exercise the *implementation*
-of the pre-processor, which is not part of the Standard).
+This set can be used as a basic check that the grammar is a valid ANTLR grammar.
 
-### 7.5.1 General
-
-```ANTLR
-// [CHANGE] Discard pre-processor directives
-PP_Directive
-    : (PP_Start PP_Kind PP_New_Line) -> skip
-    ;
-```
 
 ---
 
@@ -125,32 +52,74 @@ strive not to introduce any new ones).
 This change resolves the one remaining MLR group by inlining some of the non-terminal
 alternatives in *primary_no_array_creation_expression*.
 
-Non-terminals that are inlined are commented out and the inlined body is indented.
+Non-terminals that are inlined
+are commented out and the inlined body is indented.
 
 This change has not been made to the Standard itself as it makes *primary_no_array_creation_expression*
-“uglier” and would obfuscate somewhat the description in the Standard.
+“uglier” and would obfuscate somewhat the description in the Standard – both
+subjective reasons of course...
 
 As MLR is not supported by ANTLR without this change the grammar would be rejected.
 
-### 12.7.1 General
+### 12.8.1 General
 
 ```ANTLR
 // [CHANGE] This removes a mutual left-recursion group which we have (currently?)
-// [CHANGE] decided to leave in the Standard. Without this change the grammar will fail.
+// [CHANGE] decided to leave in the Standard. Without this change the grammar will
+// [CHANGE] fail to verify.
+# Expect
 primary_no_array_creation_expression
     : literal
+    | interpolated_string_expression
     | simple_name
     | parenthesized_expression
+    | tuple_expression
+    | member_access
+    | null_conditional_member_access
+    | invocation_expression
+    | element_access
+    | null_conditional_element_access
+    | this_access
+    | base_access
+    | post_increment_expression
+    | post_decrement_expression
+    | null_forgiving_expression
+    | object_creation_expression
+    | delegate_creation_expression
+    | anonymous_object_creation_expression
+    | typeof_expression
+    | sizeof_expression
+    | checked_expression
+    | unchecked_expression
+    | default_value_expression
+    | nameof_expression    
+    | anonymous_method_expression
+    | pointer_member_access     // unsafe code support
+    | pointer_element_access    // unsafe code support
+    | stackalloc_expression
+    ;
+# ReplaceWith
+primary_no_array_creation_expression
+    : literal
+    | interpolated_string_expression
+    | simple_name
+    | parenthesized_expression
+    | tuple_expression
     // | member_access
         | primary_no_array_creation_expression '.' identifier type_argument_list?
         | array_creation_expression '.' identifier type_argument_list?
         | predefined_type '.' identifier type_argument_list?
         | qualified_alias_member '.' identifier type_argument_list?
+    // | null_conditional_member_access
+    	| primary_no_array_creation_expression '?' '.' identifier type_argument_list? dependent_access*
+    	| array_creation_expression '?' '.' identifier type_argument_list? dependent_access*
     // | invocation_expression
         | primary_no_array_creation_expression '(' argument_list? ')'
         | array_creation_expression '(' argument_list? ')'
     // | element_access and pointer_element_access (unsafe code support)
         | primary_no_array_creation_expression '[' argument_list ']'
+    // | null_conditional_element_access
+        | primary_no_array_creation_expression '?' '[' argument_list ']' dependent_access*
     | this_access
     | base_access
     // | post_increment_expression
@@ -159,6 +128,9 @@ primary_no_array_creation_expression
     // | post_decrement_expression
         | primary_no_array_creation_expression '--'
         | array_creation_expression '--'
+    // | null_forgiving_expression
+        | primary_no_array_creation_expression null_forgiving_operator
+        | array_creation_expression null_forgiving_operator
     | object_creation_expression
     | delegate_creation_expression
     | anonymous_object_creation_expression
@@ -174,5 +146,31 @@ primary_no_array_creation_expression
         | array_creation_expression '->' identifier type_argument_list?
     // | pointer_element_access    // unsafe code support
         // covered by element_access replacement above
+    | stackalloc_expression
+    ;
+```
+
+
+---
+
+## Interpolated strings
+
+The lexical rules for interpolated strings are context-sensitive and are not ANLTR-ready in the Standard
+as how such rules are handled is an implementation detail, e.g. using ANTLR modes.
+Here we just define one token in terms of another to remove the overlap warnings.
+
+### 12.8.3 Interpolated string expressions
+
+```ANTLR
+// [CHANGE] This allows the grammar to verify without warnings, it does NOT correctly
+// [CHANGE] parse interpolated strings – that requires modes and/or lexical predicates.
+// [CHANGE] Note: Interpolated strings are properly parsed in Base and other sets.
+# Expect
+Interpolated_Verbatim_String_End
+    : '"'
+    ;
+# ReplaceWith
+Interpolated_Verbatim_String_End
+    : Interpolated_Regular_String_End
     ;
 ```

.github/workflows/do-not-merge-label-check.yml

@@ -0,0 +1,38 @@
+# This GitHub Action workflow is triggered on label changes for pull requests.
+# When a pull request is labeled with "DO NOT MERGE", the workflow fails, thus
+# preventing the pull request from being merged. Otherwise, the workflow will
+# succeed, allowing the pull request to be merged.
+
+name: "Check labels that prevent merge"
+on:
+  pull_request:
+    branches: [main]
+    types: [labeled, unlabeled]
+
+permissions:
+  contents: read
+
+jobs:
+  labels-preventing-merge-check:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        label:
+        # Labels that prevent merging
+        - 'do not merge'
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@0634a2670c59f64b4a01f0f96f84700a4088b9f0 # v2.12.0
+        with:
+          egress-policy: audit
+
+      - name: 'Check "${{ matrix.label }}" label'
+        run: |
+          echo "::notice::Merging permission is diabled for PRs when the '${{ matrix.label }}' label is applied."
+
+          if [ "${{ contains(github.event.pull_request.labels.*.name, matrix.label) }}" = "true" ]; then
+            echo "::error::Pull request is labeled as '${{ matrix.label }}'. Please remove the label before merging."
+            exit 1
+          else
+            exit 0
+          fi

.github/workflows/grammar-validator.yaml

@@ -19,23 +19,23 @@ jobs:
 
     steps:
     - name: Check out our repo
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4.2.2
 
-    - name: Setup .NET 6.0
-      uses: actions/setup-dotnet@v1
+    - name: Setup .NET 8.0
+      uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: 6.0.x
+        dotnet-version: 8.0.x
 
     - name: Set up JDK 15
-      uses: actions/setup-java@v1
+      uses: actions/setup-java@v4
       with:
         java-version: 15.0
+        distribution: zulu
 
       # Install build grammar global tool
     - name: Install BuildGrammar tool
       run: |
-        dotnet tool install --version 1.0.0-alpha.2 --global --add-source ./.github/workflows/dependencies/ EcmaTC49.BuildGrammar
-
+        dotnet tool install --version 2.1.0 --global --add-source ./.github/workflows/dependencies/ EcmaTC49.BuildGrammar
 
     - name: run validate
       run: |

.github/workflows/markdownlint.yml

@@ -28,9 +28,9 @@ jobs:
         statuses: write
 
     steps:
-    - uses: actions/checkout@24cb9080177205b6e8c946b17badbe402adc938f
+    - uses: actions/checkout@85e6279cec87321a52edac9c87bce653a07cf6c2
     - name: Use Node.js
-      uses: actions/setup-node@64ed1c7eab4cce3362f8c340dee64e5eaeef8f7c
+      uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020
       with:
         node-version: 16.x
     - name: Run Markdownlint