CSHARP-6147: Add a dotnet format check

.github/workflows/format.yml

@@ -0,0 +1,41 @@
+name: Format
+
+on:
+  pull_request:
+    branches:
+      - main
+    types:
+      - opened
+      - reopened
+      - synchronize
+
+permissions:
+  contents: read
+
+concurrency:
+  group: format-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  format:
+    name: dotnet format
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    steps:
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
+        with:
+          persist-credentials: false
+
+      - uses: actions/setup-dotnet@67a3573c9a986a3f9c594539f4ab511d57bb3ce9 # v4
+        with:
+          dotnet-version: '10.0.302'
+
+      - name: Verify formatting and code style
+        id: verify
+        run: dotnet format CSharpDriver.sln --verify-no-changes
+
+      - name: Show how to fix
+        if: failure() && steps.verify.outcome == 'failure'
+        run: |
+          echo "::error::Formatting or code style issues found. Run 'dotnet format CSharpDriver.sln' locally and commit the result."
+          echo "Some violations cannot be fixed automatically and have to be corrected by hand."

CONTRIBUTING.md

@@ -89,6 +89,25 @@ Restrict to one target with `--framework`:
 dotnet test --framework net10.0
 ```
 
+### Formatting and code style
+
+Formatting and code style come from `.editorconfig`. Most of it is reported by your IDE as you type, and some of it fails the build — but a few rules can only be checked by `dotnet format`, so CI runs it on every pull request.
+
+Check your changes, and fix them:
+
+```zsh
+dotnet format CSharpDriver.sln --verify-no-changes
+dotnet format CSharpDriver.sln
+```
+
+Some violations cannot be fixed automatically by `dotnet format` and have to be corrected by hand.
+
+Scoping the check to a single project is quicker than running it over the whole solution:
+
+```zsh
+dotnet format src/MongoDB.Bson/MongoDB.Bson.csproj --verify-no-changes
+```
+
 ## Submit a PR
 
 Push your branch to your fork once all tests pass. [Squash multiple commits into one](https://stackoverflow.com/questions/5189560/how-do-i-squash-my-last-n-commits-together) and rebase on the latest upstream first (use the "Sync fork" button on your fork's page).

src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToFilterTranslators/ExpressionTranslators/StringExpressionToRegexFilterTranslator.cs

@@ -565,8 +565,7 @@ private static AstFilter TranslateStringIndexOfComparison(TranslationContext con
                     var anyOfExpression = arguments[0];
                     anyOf = anyOfExpression.GetConstantValue<char[]>(containingExpression: expression);
                 }
-                else
-                if (method.IsOneOf(StringMethod.IndexOfWithCharOverloads))
+                else if (method.IsOneOf(StringMethod.IndexOfWithCharOverloads))
                 {
                     var valueExpression = arguments[0];
                     var value = valueExpression.GetConstantValue<char>(containingExpression: expression);