Bugfix :: Fix F# exception serialization to preserve fields by T-Gro · Pull Request #19342 · dotnet/fsharp

T-Gro · 2026-02-20T16:09:02Z

Fixes F# exceptions losing their field values during serialization.

Fixes Serialization of F#-defined exception variants doesn't serialize fields #878

Exceptions with fields now emit a GetObjectData override and a deserialization constructor that save/restore the fields via SerializationInfo, enabling correct ISerializable roundtrips.

Note: This fix is primarily relevant for users targeting .NET Framework 4.x or .NET Core ≤7, where BinaryFormatter / ISerializable serialization is still available. On .NET 8+, StreamingContext is removed and the serialization members are not emitted. The entire ISerializable infrastructure is deprecated (SYSLIB0051) — no modern serializer (System.Text.Json, DataContractSerializer, etc.) uses GetObjectData.

FSharp.Core exception caveat: FSharp.Core has [assembly: SecurityTransparent], which on .NET Framework prevents overriding the SecurityCritical method Exception.GetObjectData. FSharp.Core exceptions (e.g. MatchFailureException) therefore get only the base-call deserialization constructor (status quo) but not the GetObjectData override. This is tested explicitly. User-defined exceptions are unaffected — they get full serialization support.

github-actions · 2026-02-20T16:09:46Z

❗ Release notes required

✅ Found changes and release notes in following paths:

Change path Release notes path Description

src/Compiler docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

T-Gro · 2026-02-20T19:24:30Z

/azp run fsharp-ci

azure-pipelines · 2026-02-20T19:24:43Z

Azure Pipelines successfully started running 1 pipeline(s).

abonie · 2026-03-23T16:53:14Z

An edge case, but now this causes a runtime crash due to field name collision with Exception.GetObjectData keys

open System
open System.Runtime.Serialization

exception Foo of Message:string


let e = Foo("hello")
let info = SerializationInfo(e.GetType(), FormatterConverter())
let ctx = StreamingContext(StreamingContextStates.All)
e.GetObjectData(info, ctx)

T-Gro · 2026-03-27T08:59:06Z

Good catch! Fixed in 234f944 — serialization keys now use the backing field name (e.g. "Message@" instead of "Message"), which is guaranteed unique due to the @ suffix from CompilerGeneratedName. This avoids the collision with keys written by base.GetObjectData.

Added a dedicated test (Issue_878_ExceptionSerialization_MessageFieldCollision) that exercises exactly your repro scenario and verifies the roundtrip succeeds.

T-Gro · 2026-03-27T12:07:41Z

/azp run fsharp-ci

azure-pipelines · 2026-03-27T12:07:53Z

Azure Pipelines successfully started running 1 pipeline(s).

abonie

What happens if exception is serialized with an older compiler and deserialized with one that has these changes? If it's not going to work then perhaps this should be marked as a breaking change? Or not because it wasn't working before either?

Fixes #878 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Changed eventsWhen condition in 'Cancel running jobs with the same key' test to wait until all 10 outdated jobs are canceled and the new job finishes, instead of stopping at the first Finished event. This prevents race conditions where assertions run before all cancellations complete. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…issue #18411) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Use IL backing field name (with @ suffix) as the serialization key instead of the property name. This prevents duplicate key crashes when an F# exception field name collides with a key already used by Exception.GetObjectData (e.g., 'exception Foo of Message:string'). The backing field name (e.g., 'Message@', 'Data0@') is guaranteed to not collide with base Exception serialization keys. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Add Issue_878_ExceptionSerialization_MessageFieldCollision test that reproduces the exact edge case where an F# exception field named 'Message' collides with Exception.GetObjectData's 'Message' key. The test verifies: - GetObjectData does not throw with duplicate key - F# field is serialized under backing field name 'Message@' - Base Exception's 'Message' key remains accessible - Full serialization roundtrip preserves the field value Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Eliminate ilBaseOnlyCtorInstrs/ilBaseOnlyCtor block that duplicated ilInstrsForSerialization/ilCtorDefForSerialization by introducing shouldRestoreFields flag - Simplify 3-branch if/elif/else to 2-branch conditional - Remove unused ilPropName parameter from emitSerializationFieldIL callback Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…yIL list Replace the duplicated getActualIL helper and Assert.Contains call with a proper IL fragment in the verifyIL list, verifying the AddValue callvirt instruction is emitted in the GetObjectData method. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…rt unrelated AsyncMemoize fix - Add [CompilerGenerated] and [DebuggerNonUserCode] attributes to the generated serialization constructor and GetObjectData override on exception types, matching the pattern used by other compiler-generated methods in IlxGen. - Update verifyIL test to check for the new attributes. - Update all EmittedIL baselines (Nullness, SerializableAttribute) for both netcore and net472, debug and release configurations. - Revert unrelated AsyncMemoize flaky test fix (not part of this PR scope). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-05-13T14:00:41Z

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The push_to_pull_request_branch operation failed: Patch size (9759 KB) exceeds maximum allowed size (1024 KB). The code changes were not applied.

🤖 LabelOps — Conflict Resolution.

Merged main and resolved conflicts caused by the baseline duality elimination (#19611):

Deleted 8 old-style .debug.bsl / .release.bsl files (superseded by unified .bsl naming)
Regenerated 8 unified .bsl baselines with the serialization methods from this PR
Auto-merged cleanly: IlxGen.fs, release-notes, ComponentTests.fsproj

✅ Verified: compiler builds, SerializableAttribute tests (4) pass, exception regression tests (36) pass.

Generated by LabelOps — PR Maintenance · ● 25.9M · ◷

Resolve 8 modify/delete conflicts: delete old-style .debug.bsl/.release.bsl files superseded by unified baselines from PR #19611. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

After merging main (which eliminated debug/release baseline duality in PR #19611), regenerate the unified .netcore.bsl baselines to include the GetObjectData overrides and field-restoring deserialization constructors from this PR. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…FieldSerializationSupport (F# 11) The GetObjectData override and field-restoring deserialization constructor for exception types are now gated behind langversion 11. With langversion <=10 (the current default), exceptions emit only the base-call ctor (status quo ante PR #19342). - Add LanguageFeature.ExceptionFieldSerializationSupport, mapped to F# 11.0 - Gate shouldRestoreFields and GetObjectData emission on the feature - Update tests to use withLangVersion "11" - Update all IL baselines (SerializableAttribute, Nullness) to reflect the default-langversion output (no field serde IL) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

github-project-automation Bot added this to F# Compiler and Tooling Feb 20, 2026

T-Gro requested a review from abonie February 20, 2026 16:09

github-project-automation Bot moved this to New in F# Compiler and Tooling Feb 20, 2026

T-Gro force-pushed the codegen/fix-exception-serialization branch 3 times, most recently from c9b17c0 to f6f7424 Compare February 20, 2026 17:31

T-Gro force-pushed the codegen/fix-exception-serialization branch 2 times, most recently from 675d541 to 4b0a72e Compare February 20, 2026 19:29

T-Gro marked this pull request as ready for review March 6, 2026 11:46

T-Gro requested a review from a team as a code owner March 6, 2026 11:46

T-Gro changed the title ~~WIP :: Bugfix :: Fix F# exception serialization to preserve fields~~ Bugfix :: Fix F# exception serialization to preserve fields Mar 6, 2026

T-Gro force-pushed the codegen/fix-exception-serialization branch from 1b2f39a to 2debec9 Compare March 27, 2026 02:42

T-Gro requested review from abonie and removed request for abonie March 27, 2026 13:58

abonie reviewed Mar 30, 2026

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Comment thread tests/FSharp.Compiler.ComponentTests/CompilerService/AsyncMemoize.fs Outdated

abonie approved these changes Mar 30, 2026

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Comment thread src/Compiler/CodeGen/IlxGen.fs

github-project-automation Bot moved this from New to In Progress in F# Compiler and Tooling Mar 30, 2026

T-Gro force-pushed the codegen/fix-exception-serialization branch 5 times, most recently from 773eba0 to d485a32 Compare April 20, 2026 14:20

Fix F# exception serialization to preserve fields

053ad37

Fixes #878 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

T-Gro and others added 8 commits April 21, 2026 08:34

Retrigger CI: sole failure was known flaky test AsyncMemoize.Cancel (…

39923ae

…issue #18411) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Fix Fantomas formatting in GenExnDef serialization ctor

a95e61c

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

T-Gro force-pushed the codegen/fix-exception-serialization branch from d485a32 to bb46647 Compare April 21, 2026 06:34

T-Gro added AI-Auto-Resolve-CI Opt-in: LabelOps triages CI failures on this PR every 3h AI-Auto-Resolve-Conflicts Opt-in: LabelOps merges main into this PR and resolves conflicts every 3h labels May 12, 2026

T-Gro enabled auto-merge (squash) May 12, 2026 13:55

Copilot started work on behalf of T-Gro May 12, 2026 13:56 View session

Copilot finished work on behalf of T-Gro May 12, 2026 14:07

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[aw] No-Op Runs #19538

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T-Gro and others added 2 commits May 14, 2026 11:57

Merge origin/main into codegen/fix-exception-serialization

cc3dc95

Resolve 8 modify/delete conflicts: delete old-style .debug.bsl/.release.bsl files superseded by unified baselines from PR #19611. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

T-Gro merged commit 9661324 into main May 14, 2026
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github-project-automation Bot moved this from In Progress to Done in F# Compiler and Tooling May 14, 2026

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[release/10.0.4xx] Source code updates from dotnet/fsharp dotnet/dotnet#6612

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[main] Source code updates from dotnet/fsharp dotnet/dotnet#6628

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T-Gro mentioned this pull request May 15, 2026

Gate exception field serialization behind langversion 11 #19746

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Bugfix :: Fix F# exception serialization to preserve fields#19342

Bugfix :: Fix F# exception serialization to preserve fields#19342
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