rune/tests/test_toolchain.py

"""test_toolchain.py — SCAFFOLD-TRANCHE-003 §28 test plan (A-G)."""

import os
import sys

import pytest

sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "src"))

from rune.toolchain import (
    CONSTRAINT_KEYS,
    DecisionRecord,  # noqa: E402
    ToolchainConstraints,
    resolve_toolchain,
)


# A. existing project language strongly preferred
def test_existing_toolchain_wins():
    d = resolve_toolchain(ToolchainConstraints(existing_language="python", target_platform="linux"))
    assert d.resolution == "KEEP_EXISTING"
    assert d.selected_language == "python"
    assert d.user_approval_required is False


# B. Python selected when it's actually the project constraint (not by default)
def test_python_only_because_project_uses_it():
    d = resolve_toolchain(ToolchainConstraints(existing_language="python", performance_sensitive=False))
    assert d.selected_language == "python"
    # and Python is never picked without the project constraint or a request
    d2 = resolve_toolchain(ToolchainConstraints(target_platform="linux", deployment="server"))
    assert d2.resolution == "INSUFFICIENT_EVIDENCE"
    assert d2.selected_language == ""


# C. non-Python selected when the project clearly favors it
def test_rust_project_gets_rust():
    d = resolve_toolchain(
        ToolchainConstraints(existing_language="rust", existing_runtime="tokio", performance_sensitive=True)
    )
    assert d.selected_language == "rust"
    assert d.resolution == "KEEP_EXISTING"


def test_typescript_project_gets_typescript():
    d = resolve_toolchain(
        ToolchainConstraints(existing_language="typescript", existing_framework="svelte", target_platform="web")
    )
    assert d.selected_language == "typescript"


# D. language change requires user approval — never silent
def test_requested_change_requires_approval():
    d = resolve_toolchain(ToolchainConstraints(existing_language="python"), requested_language="rust")
    assert d.resolution == "CHANGE_MAJOR"
    assert d.user_approval_required is True
    assert d.selected_language == "rust"


def test_change_with_performance_evidence_still_requires_approval():
    d = resolve_toolchain(
        ToolchainConstraints(existing_language="python", performance_sensitive=True),
        requested_language="rust",
        performance_evidence={"significant_benefit": True, "basis": "measured 10x on streaming parse"},
    )
    assert d.user_approval_required is True


def test_same_language_request_is_not_major():
    d = resolve_toolchain(ToolchainConstraints(existing_language="python"), requested_language="python")
    assert d.resolution == "KEEP_EXISTING"
    assert d.user_approval_required is False


# E. rationale + full record persisted
def test_decision_record_is_complete_and_serializable():
    d = resolve_toolchain(
        ToolchainConstraints(existing_language="rust", existing_runtime="tokio", performance_sensitive=True),
        evidence_refs=["bench-2026-09-13"],
    )
    r = d.to_dict()
    for k in (
        "selected_language",
        "runtime",
        "rationale",
        "decisive_constraints",
        "evidence_refs",
        "confidence",
        "user_approval_required",
        "resolution",
    ):
        assert k in r
    assert "bench-2026-09-13" in r["evidence_refs"]
    assert "existing project toolchain wins" in r["rationale"]


# F. unknown constraints → INSUFFICIENT_EVIDENCE, not invented certainty
def test_unknown_constraints_insufficient():
    d = resolve_toolchain(ToolchainConstraints(target_platform="linux"))
    assert d.resolution == "INSUFFICIENT_EVIDENCE"
    assert d.selected_language == ""
    assert d.confidence == 0.0


# G. languages/runtimes/frameworks stay open-world data
def test_open_world_values_roundtrip():
    c = ToolchainConstraints(
        existing_language="zig", existing_runtime="custom-rt", wibble="future-unknown-thing"
    )  # unknown key
    assert c.unknown["wibble"] == "future-unknown-thing"
    d = resolve_toolchain(c)
    assert d.selected_language == "zig"


def test_constraint_keys_never_name_a_language():
    langs = {"python", "rust", "typescript", "go", "c++", "zig", "java"}
    assert not (CONSTRAINT_KEYS & langs)