Build Cache

FoBiS maintains a content-addressed build cache to skip recompilation when sources and flags have not changed — even across clean builds or switched working trees.

How it works

Before compiling a source file, FoBiS computes a cache key from:

Component	How it is captured
Source file commit SHA	git hash-object (or file mtime if outside git)
Active compiler name	e.g. gnu, intel
Effective cflags (normalised)	sorted, whitespace-collapsed
FoBiS version	current installed version

The key is hashed with SHA-256. If a matching object file exists in the cache store, it is copied directly to the build directory — the compiler is never invoked.

Cache location

By default the cache lives at .fobis_cache/ in the project root. Override with --cache-dir or the cache_dir fobos key:

[default]
compiler  = gnu
cache_dir = ~/.cache/fobis   # shared across projects

fobis cache subcommands

# List cached entries with sizes and timestamps
fobis cache list

# Remove entries older than N days
fobis cache clean --older-than 30

# Show the cache directory path and total size
fobis cache show

Disabling the cache

# Disable for one build
fobis build --no-cache

# Always disable via fobos
[default]
no_cache = true

When the cache invalidates

A cache entry is invalidated (and the file is recompiled) when any of the key components change:

• the source file is modified (new commit SHA or mtime)
• cflags change (e.g. switching from -O0 to -O3)
• the compiler changes (e.g. gnu → intel)
• FoBiS itself is upgraded to a new version

CI usage

The cache is most useful in local development. In CI, share it between runs using an artifact cache:

- uses: actions/cache@v4
  with:
    path: .fobis_cache
    key: fobis-${{ runner.os }}-${{ hashFiles('fobos', '**/*.F90') }}
    restore-keys: fobis-${{ runner.os }}-

Cache maintenance

Old entries accumulate over time. Prune them periodically:

# Remove entries not accessed in 60 days
fobis cache clean --older-than 60

Or add this to your CI cleanup step to keep the cached artifact small.