Implement missing tilde_assume method

[penelopeysm]

In Turing.jl v0.37, when a Gibbs sampler is used without specifying component samplers for all variables, the variables without samplers are sampled once at the beginning and don't ever move from there. See TuringLang/Turing.jl#2536.

This patch is required to preserve that behaviour - without this patch it will throw a MethodError as it was trying to look for the newly added method. Specifically it was this line in Turing.jl that was calling the missing method https://github.com/TuringLang/Turing.jl/blob/fc32e10bc17ae3fda4d7e825b6fde45dc7bdb179/src/mcmc/gibbs.jl#L162-L168

Should hopefully be simple enough to approve -- though I'm very much not a fan of how the N optional arguments force us to define 2^N methods, and it may be worth thinking about how to deal with this in a better way long-term. See also #720.

[github-actions]

Benchmark Report for Commit 8402289

Computer Information

Julia Version 1.11.5
Commit 760b2e5b739 (2025-04-14 06:53 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 4 × AMD EPYC 7763 64-Core Processor
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, znver3)
Threads: 1 default, 0 interactive, 1 GC (on 4 virtual cores)

Benchmark Results

|                 Model | Dimension |  AD Backend |      VarInfo Type | Linked | Eval Time / Ref Time | AD Time / Eval Time |
|-----------------------|-----------|-------------|-------------------|--------|----------------------|---------------------|
| Simple assume observe |         1 | forwarddiff |             typed |  false |                 10.1 |                 1.5 |
|           Smorgasbord |       201 | forwarddiff |             typed |  false |                761.0 |                32.7 |
|           Smorgasbord |       201 | forwarddiff | simple_namedtuple |   true |                423.4 |                44.4 |
|           Smorgasbord |       201 | forwarddiff |           untyped |   true |               1250.1 |                26.4 |
|           Smorgasbord |       201 | forwarddiff |       simple_dict |   true |               3248.0 |                23.8 |
|           Smorgasbord |       201 | reversediff |             typed |   true |               1473.2 |                30.1 |
|           Smorgasbord |       201 |    mooncake |             typed |   true |                964.7 |                 5.5 |
|    Loop univariate 1k |      1000 |    mooncake |             typed |   true |               5564.0 |                 4.1 |
|       Multivariate 1k |      1000 |    mooncake |             typed |   true |               1029.4 |                 8.9 |
|   Loop univariate 10k |     10000 |    mooncake |             typed |   true |              62861.5 |                 3.6 |
|      Multivariate 10k |     10000 |    mooncake |             typed |   true |               8802.3 |                10.1 |
|               Dynamic |        10 |    mooncake |             typed |   true |                131.7 |                13.8 |
|              Submodel |         1 |    mooncake |             typed |   true |                 13.6 |                 6.8 |
|                   LDA |        12 | reversediff |             typed |   true |                461.6 |                 6.9 |

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.01%. Comparing base (6cd439d) to head (8402289).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/context_implementations.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #904      +/-   ##
==========================================
- Coverage   85.05%   85.01%   -0.05%     
==========================================
  Files          35       35              
  Lines        3922     3924       +2     
==========================================
  Hits         3336     3336              
- Misses        586      588       +2     

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[coveralls]

Pull Request Test Coverage Report for Build 14698049682

Details

• 0 of 2 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.04%) to 85.102%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/context_implementations.jl	0	2	0.0%

Totals
Change from base Build 14669950832:	-0.04%
Covered Lines:	3336
Relevant Lines:	3920

---

💛 - Coveralls

[mhauru]

👍