[xperiandri]

Fixes #2758

Stacked on #20895

db.Orders.Any(fun o -> o.CustomerId = c.Id) in a query's where, or a second for over db.Orders.Where(fun o -> ..), now reaches the provider as an ordinary subquery instead of a call that converts the inner lambda when the tree runs.

Details

• A lambda nested in a lambda that goes to a provider is converted together with it and quoted, as the C# compiler does, when it reads a parameter of the outer lambda.
• A nested lambda that reads none keeps the run-time call. It depends on nothing the provider translates, so EF Core and Cosmos evaluate it up front like any captured value, and a method of your own that takes an expression keeps working inside a query.
• A nested lambda that cannot be converted keeps the call as well, whatever the conversion fails with, and fails only if the tree gets to run it.

🤖 Generated with Claude Code

[github-actions]

✅ Release notes checked

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
`src/FSharp.Core`	docs/release-notes/.FSharp.Core/11.0.200.md

[xperiandri]

Covered cases

EF Core SQLite translates 132 of 154 scenarios, 123 on #20895. Now translated: where, Select and SelectMany with a lambda over another source, a second for over a source filtered by a lambda, All and Count over another source, a nested lambda that reads a let naming a member, and a lambda nested two levels deep.

Unchanged: a method that takes an expression and reads nothing of the query still runs inside a query.

[Copilot]

🟡 Changes recommended

Active findings show that let-binding rewrites can reorder side effects and mutate source structs instead of local copies.

4 open issues

• Preserve explicit effectful lets in record field conversion · New
• Restrict named-local mutation exception to predefined value types · New
• Substitute safe let aliases before deciding whether to quote · New
• Handle unresolved selectors without crashing the analyzer · New

What changed in this PR

This PR updates FSharp.Core’s LINQ conversion so nested lambdas that capture an enclosing lambda parameter reach providers as quoted expressions. It builds on the stacked changes for struct tuples and provider-friendly let bindings.

Changes:

• Quote correlated nested lambdas while preserving runtime conversion for independent or unsupported lambdas.
• Include struct-tuple support and selective let substitution from the preceding changes.
• Add expression-shape and evaluation tests, plus compatibility documentation.

File	Description
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​QueryStructureScenarios.fs	Covers nested queries, loops, and left joins.
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​QueryShapeTests.fs	Runs the query scenario suites.
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​QueryScenarioDomain.fs	Defines shared query data and fixtures.
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​QueryScenario.fs	Checks query results and expression shapes.
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​QueryProviderShape.fs	Captures queries and detects problematic expression nodes.
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​QueryProjectionScenarios.fs	Covers tuple, record, and object projections.
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​QueryOperatorScenarios.fs	Covers filtering, ordering, joins, and aggregates.
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​QueryMethodSyntaxScenarios.fs	Covers LINQ method syntax and correlated lambdas.
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​QueryKeyScenarios.fs	Covers composite join and grouping keys.
tests/​FSharp.Core.UnitTests/​FSharp.Core/​Microsoft.FSharp.Linq/​ExpressionLambdaConversionTests.fs	Checks quoting, substitution, and evaluation semantics.
tests/​FSharp.Core.UnitTests/​FSharp.Core.UnitTests.fsproj	Registers the new test files.
src/​FSharp.Core/​QueryExtensions.fs	Preserves struct-tuple identity during query adaptation.
src/​FSharp.Core/​Query.fs	Integrates expression conversion and projection rewriting.
src/​FSharp.Core/​Linq.fsi	Declares shared internal conversion helpers.
src/​FSharp.Core/​Linq.fs	Implements nested-lambda quoting and selective substitution.
docs/​release-notes/​PENDING_BREAKING_CHANGES.md	Documents expression-shape and evaluation changes.
docs/​release-notes/​.FSharp.Core/​11.0.200.md	Adds release notes for the LINQ fixes.

_{Review effort: Balanced}

[xperiandri]

Fixed in 31c93a1 (#20895), covered here in c9c710b. A let of plain arithmetic (+, -, * on constants and reads) is now replaced by its value before the body is converted, so let n = x + 1 in LinqExpr.FromFunc(fun y -> y + n) quotes the nested lambda and has no block. A let that is not a read keeps its block and is evaluated once: let n = counter.Next() + x is a test. The operands are never arithmetic themselves, so a value built on another one does not grow with every let.