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[exec] on/continues_on hits __not_a_scheduler diagnostics under the debug environment when STDEXEC_ENABLE_EXTRA_TYPE_CHECKING=ON

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
cpp
Domain
backend

Research direction

Reproduce the failure with exec::any_sequence_sender and exec::on or exec::continues_on using -DSTDEXEC_ENABLE_EXTRA_TYPE_CHECKING=ON. Trace the extra-type-checking debug environment and its scheduler-query lookup; done means these transformations no longer produce __not_a_scheduler diagnostics while scheduler queries still reach the wrapped environment.

Written by the indexing model from the issue text.

Description

Requested by @ericniebler in #2271 — follow-up found while verifying that PR with -DSTDEXEC_ENABLE_EXTRA_TYPE_CHECKING=ON. Fails on pristine main, so it is separate from the fix in #2271.

Description

Pipelines that transform sequence senders with exec::on / exec::continues_on produce __not_a_scheduler diagnostics under extra type checking. The debug environment injected by the extra-type-checking machinery appears to shadow or alter scheduler-related queries, so the transformation's scheduler lookup sees the debug proxy environment instead of the real one and concludes there is no scheduler.

Reproduction

Compose an exec::any_sequence_sender with exec::on / exec::continues_on and build with -DSTDEXEC_ENABLE_EXTRA_TYPE_CHECKING=ON.

Suggested fix direction

Make the debug env forwarding query-aware for scheduler queries (forward get_scheduler / get_delegatee_scheduler to the wrapped environment), or exclude scheduler queries from the debug proxy.

Dominant language
C++
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Forks
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Avg merge
2d 17h
Merged PRs (30d)
37

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