Decompile await on dynamic expressions#3872
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Awaiting a dynamic value lowers GetAwaiter/IsCompleted/GetResult to dynamic callsites, which async decompilation could not recognize: await detection ran before DynamicCallSiteTransform, so the await was emitted as a raw state machine (or crashed in AnalyzeAwaitBlock, #1388). AnalyzeStateMachine now collapses the awaiter callsites per block, folds the runtime ICriticalNotifyCompletion branch the compiler emits for an awaiter not statically known to implement it into the canonical single call, and re-joins the branch chains the collapse leaves so each dynamic await sits in one block. DetectAwaitPattern matches the dynamic GetAwaiter/IsCompleted/GetResult shape and emits `await expr`; a synthesized dynamic GetResult method gives the await and its local the dynamic type. DynamicCallSiteTransform also follows callsite targets spilled into state-machine locals, so an awaited value flowing into a dynamic callsite (e.g. d.Result = await ..., #1928) decompiles too. Assisted-by: Claude:claude-fable-5:Claude Code
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Pull request overview
This PR enhances ILSpy’s async/await decompiler so it can recognize and emit await when the awaited value/awaiter is dynamic, avoiding raw state-machine output and fixing crashes in await analysis for dynamic callsite-based awaiters.
Changes:
- Normalizes compiler-emitted dual-branch
AwaitOnCompleted/AwaitUnsafeOnCompletedpatterns so await analysis can proceed consistently even when the awaiter type isn’t statically known. - Extends await-pattern detection to match dynamic
GetAwaiter/IsCompleted/GetResultcallsite shapes and propagatedynamictyping through the await. - Enhances dynamic callsite transformation to follow callsite targets spilled across awaits and adds a new
DynamicAwaitpretty-test fixture + runner entry.
Reviewed changes
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| File | Description |
|---|---|
| ICSharpCode.Decompiler/IL/Transforms/IntroduceDynamicTypeOnLocals.cs | Marks locals as dynamic when they participate in a dynamic await, improving type reconstruction. |
| ICSharpCode.Decompiler/IL/Transforms/DynamicCallSiteTransform.cs | Refactors callsite detection/transform; adds per-basic-block entrypoint used during async analysis. |
| ICSharpCode.Decompiler/IL/ControlFlow/ControlFlowSimplification.cs | Exposes block-combine helper for reuse by async decompiler post-processing. |
| ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs | Normalizes dynamic awaiter runtime branches, detects dynamic await patterns, synthesizes dynamic awaiter methods, and coalesces blocks post-transform. |
| ICSharpCode.Decompiler.Tests/TestCases/Pretty/DynamicAwait.cs | Adds new pretty-test cases covering dynamic awaiters and dynamic operations around/through awaits. |
| ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs | Wires up the new DynamicAwait pretty-test suite. |
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| Dictionary<IField, CallSiteInfo> callsites = new Dictionary<IField, CallSiteInfo>(); | ||
| FindDynamicCallSitesInBlock(block, callsites, context); | ||
| // Deleting the now-unreachable callsite-init blocks is deferred to the SortBlocks call | ||
| // at the end of AsyncAwaitDecompiler.AnalyzeStateMachine: this runs while that method is | ||
| // iterating over the container's blocks, so removing blocks here would corrupt the loop. | ||
| TransformCallSites((BlockContainer)block.Parent, callsites, context); |
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Awaiting a dynamic value was not decompiled. Because the async decompiler runs before
DynamicCallSiteTransform,GetAwaiter/IsCompleted/GetResultwere still dynamic callsites that await detection could not recognize, so the method was emitted as a raw state machine (or crashed inAnalyzeAwaitBlock, #1388).What changed
AnalyzeStateMachinecollapses the awaiter callsites per block, folds the runtimeICriticalNotifyCompletionbranch the compiler emits for an awaiter not statically known to implement it into the canonical single call, and re-joins the branch chains the collapse leaves so each dynamic await sits in a single block.DetectAwaitPatternmatches the dynamicGetAwaiter/IsCompleted/GetResultshape and emitsawait expr. A synthesized dynamicGetResultmethod gives the await (and the awaited local) thedynamictype.DynamicCallSiteTransformfollows callsite targets spilled into state-machine locals across an await, so an awaited value flowing into a dynamic callsite (e.g.d.Result = await ..., dynamic JObject() not decompile correctly #1928) decompiles too.Tests
New
DynamicAwaitpretty-test fixture covering dynamic awaiters (await d,await d.RunAsync()), dynamic operations around an await, and awaited values feeding a dynamic set-member/invoke/index/binary-op/convert. FullAsync*+DynamicTests+DynamicAwaitpretty-test suites pass with no regression.Fixes #1388
Fixes #1928
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