Fix Homebrew install:

[sbryngelson]

add fallback constants when m_constants.fpp is unavailable

The Homebrew formula only ships toolchain/ and examples/, but not src/. The toolchain reads Fortran constants from src/common/m_constants.fpp at import time, causing a RuntimeError in Homebrew installs. Add fallback values for the 4 required constants so the toolchain works without the Fortran source tree.

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[qodo-code-review]

Review Summary by Qodo

Add fallback Fortran constants for Homebrew compatibility

🐞 Bug fix ✨ Enhancement

Walkthroughs

Description

• Add fallback Fortran constants for Homebrew installations
• Prevents RuntimeError when src/common/m_constants.fpp unavailable
• Maintains compatibility with incomplete Homebrew package distribution
• Includes 4 required constants with documented sync requirement

Diagram

flowchart LR
  A["get_fortran_constants()"] --> B["Parse m_constants.fpp"]
  B --> C{"Constants found?"}
  C -->|Yes| D["Return parsed constants"]
  C -->|No| E["Use _FALLBACK_CONSTANTS"]
  E --> F["Return fallback values"]

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File Changes

1. toolchain/mfc/params/namelist_parser.py 🐞 Bug fix +14/-1

Add fallback constants for missing Fortran source

• Updated get_fortran_constants() docstring to clarify fallback behavior for Homebrew installs
• Added fallback logic to use _FALLBACK_CONSTANTS when parsing returns empty dict
• Introduced _FALLBACK_CONSTANTS dictionary with 4 required constants: num_fluids_max,
 num_probes_max, num_patches_max, num_bc_patches_max
• Added comment noting fallback values must stay synchronized with src/common/m_constants.fpp

toolchain/mfc/params/namelist_parser.py

---

[qodo-code-review]

Code Review by Qodo

🐞 Bugs (1) 📘 Rule violations (0) 📎 Requirement gaps (0) 🎨 UX Issues (0)

1. Fallback masks parse failures 🐞 Bug ≡ Correctness

Description

get_fortran_constants() falls back to hardcoded values whenever parse_fortran_constants() returns an
empty dict, which happens both when src/common/m_constants.fpp is missing and when the parser fails
to match anything. This can silently hide toolchain/Fortran drift that params/definitions.py
explicitly intends to fail fast on, potentially leading to incorrect registry bounds and validation
limits.

Code

toolchain/mfc/params/namelist_parser.py[R501-502]

+        if not _FORTRAN_CONSTANTS_CACHE:
+            _FORTRAN_CONSTANTS_CACHE = _FALLBACK_CONSTANTS.copy()

Evidence

parse_fortran_constants() returns an empty dict both on FileNotFoundError and when the regex finds
no matches, and get_fortran_constants() treats any empty dict as “source unavailable” and silently
substitutes fallback values. Meanwhile, params/definitions.py is designed to raise a RuntimeError
when required constants are missing to ensure the toolchain stays in sync with Fortran; the new
behavior can defeat that safety check in some failure modes.

toolchain/mfc/params/namelist_parser.py[467-482]
toolchain/mfc/params/namelist_parser.py[489-503]
toolchain/mfc/params/definitions.py[15-24]
src/common/m_constants.fpp[19-28]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

### Issue description
`get_fortran_constants()` currently falls back to `_FALLBACK_CONSTANTS` whenever `parse_fortran_constants()` returns an empty dict. Since `parse_fortran_constants()` returns `{}` both when the file is missing and when parsing finds no matches, this can silently mask real parsing failures / format drift.

### Issue Context
The toolchain uses these constants at import time in `params/definitions.py` and is intended to fail fast when constants can’t be parsed (to stay in sync with Fortran). The fallback should apply only when the Fortran source tree is genuinely unavailable.

### Fix Focus Areas
- toolchain/mfc/params/namelist_parser.py[467-503]
- toolchain/mfc/params/definitions.py[15-24]

### Suggested fix
1. In `parse_fortran_constants`, return `None` (or raise a dedicated exception) on `FileNotFoundError`, and return a dict (possibly empty) only for successful reads.
2. In `get_fortran_constants`, fall back only when the file is missing (`None` / explicit missing condition). If the file exists but parsing yields no constants, raise a clear `RuntimeError` indicating the parser is out of sync with `m_constants.fpp` (or at least emit a warning).
3. (Optional) Add a small unit test that simulates: (a) missing file => fallback, (b) existing file with non-matching content => error/warn.

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Caution

Review failed

The pull request is closed.

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📥 Commits

Reviewing files that changed from the base of the PR and between fbaa8c6 and c4ad2ea.

📒 Files selected for processing (1)

• toolchain/mfc/params/namelist_parser.py

---

📝 Walkthrough

Walkthrough

The get_fortran_constants() function in the namelist parser module is updated to include a fallback mechanism. When parsing the Fortran constants file fails or returns no results, the function now uses a predefined fallback constants dictionary containing num_fluids_max, num_probes_max, num_patches_max, and num_bc_patches_max instead of returning empty. The function signature remains unchanged, and the docstring is updated to document this fallback behavior.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.88%. Comparing base (cf81f25) to head (c4ad2ea).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1355      +/-   ##
==========================================
+ Coverage   64.85%   64.88%   +0.03%     
==========================================
  Files          70       70              
  Lines       18228    18249      +21     
  Branches     1506     1507       +1     
==========================================
+ Hits        11821    11841      +20     
  Misses       5446     5446              
- Partials      961      962       +1     

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