fprime-fpp-python

Native Python bindings to the FPP compiler. Installed as fprime-fpp-python, imported as fpp.

The extension binds directly to the Rust FPP compiler via PyO3.

Installation

pip install fprime-fpp-python

An abi3 wheel, usable on CPython ≥ 3.10. Building from source needs Rust ≥ 1.85 and maturin.

Usage

import fpp

model = fpp.analyze(source="""
module M {
  array Arr = [4] U32
  constant answer = 6 * 7
}
""")

model.has_errors                             # False
for d in model.diagnostics:
    d.level                                  # fpp.DiagnosticLevel.Error
    print(d.display)                         # 'path:line:col: error: message'
    print(d)                                 # the compiler's console rendering

(unit,) = model.ast                          # one translation unit per input
(module,) = unit.members
[type(m).__name__ for m in module.members]   # ['DefArray', 'DefConstant']

arr = model.lookup("M.Arr")                                     # SymbolArrayType
arr.definition.resolved_type.array_size                         # 4
model.lookup("M.answer").definition.value.resolved_value.value  # 42

All inputs to one call are analyzed together. A bare string is a path, source= is text, and imports= — the counterpart of fpp-to-cpp -i — is analyzed the same way but is not part of what you asked about:

model = fpp.analyze(["MyComponent.fpp"], imports=["Fw/Fw.fpp"])
[u.uri for u in model.ast if u.is_source]    # ['MyComponent.fpp']

parse is the fast front end: it stops after include resolution, so you get syntax and nothing resolved.

tree = fpp.parse(["A.fpp", "B.fpp"])
[u.uri for u in tree.units]                  # ['A.fpp', 'B.fpp']

Subclass AstVisitor and override visit_<type(node).__name__>. Traversal is deep by default: super() descends, omitting it prunes.

class Constants(fpp.AstVisitor):
    def __init__(self):
        self.values = {}

    def visit_DefConstant(self, node):
        self.values[node.name] = node.value.resolved_value.value
        super().visit_DefConstant(node)

consts = Constants()
consts.visit(model)                          # or a SyntaxTree, TransUnit, or node
consts.values                                # {'answer': 42}

Semantic types are closed unions, so narrow them with isinstance or match rather than a string tag.

match arr.definition.resolved_type:
    case fpp.ArrayType() as a:
        elt = a.anon_array.elt_type
        isinstance(elt, fpp.PrimitiveIntType) and elt.value == fpp.IntegerKind.U32

Findings of your own report like compiler errors: build a Diagnostic against any node's span, add child annotations and notes, and print it.

node = model.lookup("M.answer").definition
print(fpp.Diagnostic(
    "answer is unused", level=fpp.DiagnosticLevel.Warning,
    span=node.span,
    children=[fpp.DiagnosticMessage("delete it")],
))
#  --> mem.fpp:4:3
#   |
# 4 |   constant answer = 6 * 7
#   |   ^^^^^^^^^^^^^^^^^^^^^^^ answer is unused
#   |
#   = note: delete it

A check can raise its finding instead of returning it: fpp.DiagnosticError carries a Diagnostic, and everything on that diagnostic stays writable, so each handler on the way out can add the context it knows.

try:
    check_component(instance.component)
except fpp.DiagnosticError as error:
    error.diagnostic.add_note("in this instance", span=instance.node.span)
    raise

fpp.pyi is the reference for the rest — every class, getter and return type — and the docstrings carry the contracts: help(fpp.analyze), help(fpp.Model), help(fpp.AstVisitor).

Development

A Cargo workspace member of fpp-tools. The node wrappers and the recording walk are expanded by fpp_python_macros from checked-in declarations (src/ast/defs.rs, src/sem/defs.rs); the core (pipeline, ir_core, lower_core, noderef, model, visitor, diagnostics) is hand-written.

Those declarations and fpp.pyi are generated and checked in — change the generator or the macro, never the file, and re-run make. CI fails on drift.

maturin develop            # build + install into the active venv
pytest tests/              # run the tests

make nightly               # one-time: the nightly the bindgen's rustdoc needs
make                       # regenerate the declarations, then the stub
make help                  # the individual codegen targets

The bindgen reflects fpp_analysis from rustdoc JSON, whose schema is unstable, so the nightly is pinned exactly — in fpp_python_bindgen/nightly-toolchain alongside the rustdoc-types pin in its Cargo.toml. Bump the two together. FPP_BINDGEN_TOOLCHAIN overrides the toolchain for a one-off run.