# Decisions — tofu-core

Architectural choices and rationales discovered during work on this plan.

_Auto-scaffolded by /start-work. Append new entries below - never overwrite._

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### Task 4: `version` → `ver` rename
`version` is a reserved keyword in D (conditional compilation). All struct fields bearing this name are renamed to `ver` — PackageIndex.ver, Recipe.ver, DepConstraint.ver, CacheManifest.ver, BinaryCheckResult.ver. This keeps the API readable while avoiding the keyword conflict. Downstream modules referencing these structs must use `.ver` for the version field.

### Task 4: DepConstraint uses typed `DepOp` enum, not string op
The Lua reference stores `op` as a string (`nil`, `">="`, `"=="`, etc.). In D we use a typed `DepOp` enum (`ge, le, eq, ne, gt, lt, none`) for type safety and exhaustive switching. The `parse` factory handles string-to-enum conversion at parse time.

### Task 4: BuildPlan is a plain container — no sorting
The plan specifies that `order()` returns entries in deps-first order *guaranteed by the caller*. The struct itself is just a container with `add()` and `order()` — no topological sort or dependency resolution. Sorting logic belongs in a later module (`tofu.resolver` or similar).

### Task 4: Single exception type `TypesException`
One exception class for the entire types module — no separate subclasses per error category. The parse failures (bad dep spec, invalid pool) all throw `TypesException` with a descriptive message. Callers catch `TypesException` for all type-parsing errors.

### Task 4: Manual char scanning for dep spec parsing
Rather than pulling in `std.regex`, the parser uses hand-written `isNameChar()` and `isWhite()` helpers with a simple position cursor. This keeps the module dependency-light (only `std.ascii`). The logic is a direct 1:1 port of the Lua reference patterns: `[A-Za-z0-9_.+-]` for names/versions, whitespace `[ \t]` for separators.

### Task 12: `delegate` keyword in test lambdas for delegate-typed parameters
D non-capturing lambdas infer as `function` pointers, which cannot implicitly convert to `delegate`-typed parameters. The explicit `delegate` keyword (`scope f = delegate (...) { ... };`) forces the correct type. This pattern is needed for resolution seam delegates that production code will instantiate with captures (e.g. closing over `Config cfg`).

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### Task 26: Error-to-exit-code mapping via marker fields, not string inspection

**Decision: bool marker fields on exception classes instead of string-content inspection in `exitCodeFor`.**

The plan initially suggested checking `e.msg.indexOf("not found")` to distinguish exit code 2 (package not found) from exit code 6 (network error) for `FetchException`.  Instead, each exception class carries a boolean marker:
- `BuildException.toolMissing` — distinguishes tool-not-found (exit 7) from build failure (exit 4).
- `InstallException.toolMissing` — distinguishes tool-not-found (exit 7) from install failure (exit 5).
- `FetchException.notFound` — distinguishes package-not-found (exit 2) from network error (exit 6).

**Rationale**: String inspection is fragile — error messages may change, use different formatting, or get truncated.  A dedicated field communicates intent unambiguously and survives message refactoring.

### Task 26: `TofuError` base class for explicit-exit exceptions

Rather than a separate `throwExit(int, string)` helper, `TofuError : Exception` with an `int exitCode` field lets callers throw the exception and have `exitCodeFor` read the code directly.  This keeps the exit-mapping logic centralized (always go through `exitCodeFor`) while allowing callers to set explicit codes when they know them (e.g. in command stubs).

### Task 26: Lock file at `<cacheDir>/.lock` with PID-liveness check

The lock uses `kill(pid, 0)` (POSIX signal 0) to test whether the locking PID is still alive.  A dead PID means the lock is stale and can be safely removed.  This avoids the need for a separate lock-daemon or file-lock (flock/fcntl).

**Conservative assumption**: If `kill(pid, 0)` fails with anything other than ESRCH (e.g. EPERM), the PID is assumed alive.  This errs on the side of safety — false-positive "another process" is better than concurrent writes.

### Task 26: `not implemented yet` stubs in dispatch for commands 20–24

Commands 20–24 (search, install, upgrade, remove, info) are separate tasks running in parallel.  Since D cannot conditionally import modules at compile time, main.d dispatches via `final switch` on the `Command` enum with all cases present.  For commands whose modules don't exist yet, a `logError("command '<x>' not implemented yet")` + `return 1` stub is used.  These stubs are documented and will be replaced when tasks 20–24 land.

### Task 26: `write(2, ...)` POSIX syscall for signal handler, not `stderr.rawWrite`

DMD 2.112's `core.sys.posix.signal.signal` requires the handler to be `@nogc`.  `std.stdio.File.rawWrite` is NOT `@nogc` (File is a GC-managed class).  Instead, the handler uses the raw POSIX `write(2, msg.ptr, msg.length)` syscall from `core.sys.posix.unistd`, which is a direct C call and fully `@nogc`.

Similarly, `_exit(130)` from `core.sys.posix.unistd` is used instead of `core.stdc.stdlib.exit` — `_exit` does NOT run atexit handlers or flush stdio buffers, making it safe in a signal-handler context.

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