make eltype more concrete when merging metadata

[penelopeysm]

another fix, mainly motivated by getting enzyme working on gibbs on 1.10, but probably just generally good to make the eltype as tight as possible (a lesson we learnt for VNV but never backported for metadata)

[github-actions]

Benchmark Report

• this PR's head: 69795a636b0ac86264be6f98e91ae6d8a1d0dd12
• base branch: 55c3225ceff65d85bd48c5d275d1902fa1508cc9

Computer Information

Julia Version 1.11.8
Commit cf1da5e20e3 (2025-11-06 17:49 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

┌───────────────────────┬───────┬─────────────┬───────────────────┬────────┬─────────────────────────────────┬────────────────────────────┬─────────────────────────────────┐
│                       │       │             │                   │        │        t(eval) / t(ref)         │     t(grad) / t(eval)      │        t(grad) / t(ref)         │
│                       │       │             │                   │        │ ──────────┬───────────┬──────── │ ───────┬─────────┬──────── │ ──────────┬───────────┬──────── │
│                 Model │   Dim │  AD Backend │           VarInfo │ Linked │      base │   this PR │ speedup │   base │ this PR │ speedup │      base │   this PR │ speedup │
├───────────────────────┼───────┼─────────────┼───────────────────┼────────┼───────────┼───────────┼─────────┼────────┼─────────┼─────────┼───────────┼───────────┼─────────┤
│               Dynamic │    10 │    mooncake │             typed │   true │    383.63 │    349.83 │    1.10 │   9.32 │   10.40 │    0.90 │   3573.54 │   3639.01 │    0.98 │
│                   LDA │    12 │ reversediff │             typed │   true │   2648.04 │   2475.15 │    1.07 │   5.09 │    4.97 │    1.02 │  13481.28 │  12294.20 │    1.10 │
│   Loop univariate 10k │ 10000 │    mooncake │             typed │   true │ 103049.73 │ 100233.92 │    1.03 │   3.89 │    3.94 │    0.99 │ 400849.93 │ 395226.96 │    1.01 │
├───────────────────────┼───────┼─────────────┼───────────────────┼────────┼───────────┼───────────┼─────────┼────────┼─────────┼─────────┼───────────┼───────────┼─────────┤
│    Loop univariate 1k │  1000 │    mooncake │             typed │   true │   7815.85 │   7444.87 │    1.05 │   4.75 │    4.54 │    1.05 │  37093.65 │  33775.28 │    1.10 │
│      Multivariate 10k │ 10000 │    mooncake │             typed │   true │  31642.23 │  29906.59 │    1.06 │  10.36 │   10.23 │    1.01 │ 327703.20 │ 305933.52 │    1.07 │
│       Multivariate 1k │  1000 │    mooncake │             typed │   true │   3587.06 │   3302.24 │    1.09 │  13.13 │    9.36 │    1.40 │  47094.00 │  30922.31 │    1.52 │
├───────────────────────┼───────┼─────────────┼───────────────────┼────────┼───────────┼───────────┼─────────┼────────┼─────────┼─────────┼───────────┼───────────┼─────────┤
│ Simple assume observe │     1 │ forwarddiff │             typed │  false │      2.73 │      2.51 │    1.09 │   3.88 │    3.95 │    0.98 │     10.58 │      9.93 │    1.07 │
│           Smorgasbord │   201 │ forwarddiff │             typed │  false │   1228.14 │   1135.37 │    1.08 │  62.43 │  122.07 │    0.51 │  76676.85 │ 138594.74 │    0.55 │
│           Smorgasbord │   201 │ forwarddiff │       simple_dict │   true │       err │       err │     err │    err │     err │     err │       err │       err │     err │
├───────────────────────┼───────┼─────────────┼───────────────────┼────────┼───────────┼───────────┼─────────┼────────┼─────────┼─────────┼───────────┼───────────┼─────────┤
│           Smorgasbord │   201 │ forwarddiff │ simple_namedtuple │   true │       err │       err │     err │    err │     err │     err │       err │       err │     err │
│           Smorgasbord │   201 │      enzyme │             typed │   true │   1696.45 │   1577.26 │    1.08 │   5.63 │    6.97 │    0.81 │   9551.92 │  10993.00 │    0.87 │
│           Smorgasbord │   201 │    mooncake │             typed │   true │   1674.23 │   1588.15 │    1.05 │   5.33 │    5.16 │    1.03 │   8928.31 │   8188.39 │    1.09 │
├───────────────────────┼───────┼─────────────┼───────────────────┼────────┼───────────┼───────────┼─────────┼────────┼─────────┼─────────┼───────────┼───────────┼─────────┤
│           Smorgasbord │   201 │ reversediff │             typed │   true │   1671.93 │   1586.69 │    1.05 │  92.51 │   89.53 │    1.03 │ 154674.32 │ 142056.45 │    1.09 │
│           Smorgasbord │   201 │ forwarddiff │      typed_vector │   true │   1666.32 │   1568.50 │    1.06 │ 129.04 │   65.90 │    1.96 │ 215029.34 │ 103361.93 │    2.08 │
│           Smorgasbord │   201 │ forwarddiff │           untyped │   true │   1694.08 │   1562.58 │    1.08 │  60.33 │   56.22 │    1.07 │ 102209.96 │  87850.23 │    1.16 │
├───────────────────────┼───────┼─────────────┼───────────────────┼────────┼───────────┼───────────┼─────────┼────────┼─────────┼─────────┼───────────┼───────────┼─────────┤
│           Smorgasbord │   201 │ forwarddiff │    untyped_vector │   true │   1691.70 │   1555.28 │    1.09 │  60.17 │   55.98 │    1.07 │ 101793.01 │  87070.11 │    1.17 │
│              Submodel │     1 │    mooncake │             typed │   true │      7.19 │      6.72 │    1.07 │   5.24 │    5.33 │    0.98 │     37.66 │     35.83 │    1.05 │
└───────────────────────┴───────┴─────────────┴───────────────────┴────────┴───────────┴───────────┴─────────┴────────┴─────────┴─────────┴───────────┴───────────┴─────────┘

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.89%. Comparing base (55c3225) to head (69795a6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1188      +/-   ##
==========================================
+ Coverage   78.79%   78.89%   +0.10%     
==========================================
  Files          41       41              
  Lines        3914     3914              
==========================================
+ Hits         3084     3088       +4     
+ Misses        830      826       -4     

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[github-actions]

DynamicPPL.jl documentation for PR #1188 is available at:
https://TuringLang.github.io/DynamicPPL.jl/previews/PR1188/