Appearance
| 1 | namespace Syntax.Process is | |
| 2 | use Semantic.Types.Type; | |
| 3 | use Semantic.Types.INTERSECTION; | |
| 4 | use Symbol = Semantic.Symbols.Symbol; | |
| 5 | ||
| 6 | // The flow-analysis facts in force at one program point: the | |
| 7 | // local variables observed at a type narrower than their | |
| 8 | // declaration, the local variables known to be definitely | |
| 9 | // assigned, the local variables known to hold a value, and a | |
| 10 | // `bottom` marker for points reached only via a diverging path | |
| 11 | // (return / throw / break / continue). | |
| 12 | // | |
| 13 | // The flow pass threads a NARROW_ENV forward through a method, | |
| 14 | // copies it at branch points, and merges divergent copies with | |
| 15 | // `join`. A variable absent from `_narrows` is at its declared | |
| 16 | // type; a variable absent from `_assigned` is not known to be | |
| 17 | // definitely assigned; a variable absent from `_non_null` is not | |
| 18 | // known to hold a value. See `docs/claude/flow-sensitive-narrowing.md`. | |
| 19 | class NARROW_ENV is | |
| 20 | _narrows: Collections.MAP[Symbol, Type]; | |
| 21 | ||
| 22 | // Locals definitely assigned on every path reaching this | |
| 23 | // point — the definite-assignment domain. | |
| 24 | _assigned: Collections.SET[Symbol]; | |
| 25 | ||
| 26 | // Locals known to hold a value at this point — non-null for a | |
| 27 | // reference type, has-a-value for a NULLABLE[T] (`T?`) value | |
| 28 | // type. The presence domain; a possible-null-dereference | |
| 29 | // check (a later phase) consumes it. | |
| 30 | _non_null: Collections.SET[Symbol]; | |
| 31 | ||
| 32 | // Member-access paths (`receiver.prop`, `receiver.a.b`) known | |
| 33 | // to hold a value at this point — the same presence domain | |
| 34 | // lifted from single symbols to re-readable paths. A path | |
| 35 | // here is narrowed optional -> non-optional at its use sites, | |
| 36 | // so `if x.y? then x.y.z fi` type-checks. Every hop is a | |
| 37 | // field or a store-free getter; the flow transfers drop paths | |
| 38 | // the moment the heap may have changed what they read. See | |
| 39 | // ACCESS_PATH. | |
| 40 | _non_null_paths: Collections.SET[ACCESS_PATH]; | |
| 41 | ||
| 42 | // Member-access paths narrowed to a specific type at this | |
| 43 | // point — the type domain lifted from single symbols to | |
| 44 | // re-readable paths. A path here is loaded at the narrower | |
| 45 | // type at its use sites, so `if isa Cat(x.y) then x.y.meow() | |
| 46 | // fi` type-checks. Composed via INTERSECTION like `_narrows`, | |
| 47 | // and dropped by the same heap transfers as `_non_null_paths`. | |
| 48 | _path_narrows: Collections.MAP[ACCESS_PATH, Type]; | |
| 49 | ||
| 50 | // True for an unreachable program point. A bottom env is the | |
| 51 | // identity element of `join` and carries no facts. | |
| 52 | is_bottom: bool public; | |
| 53 | ||
| 54 | init() is | |
| 55 | _narrows = Collections.MAP[Symbol, Type](); | |
| 56 | _assigned = Collections.SET[Symbol](); | |
| 57 | _non_null = Collections.SET[Symbol](); | |
| 58 | _non_null_paths = Collections.SET[ACCESS_PATH](); | |
| 59 | _path_narrows = Collections.MAP[ACCESS_PATH, Type](); | |
| 60 | si | |
| 61 | ||
| 62 | // The unreachable environment. | |
| 63 | bottom() -> NARROW_ENV static is | |
| 64 | let e = NARROW_ENV(); | |
| 65 | e.is_bottom = true; | |
| 66 | return e; | |
| 67 | si | |
| 68 | ||
| 69 | is_empty: bool => !is_bottom /\ _narrows.count == 0; | |
| 70 | count: int => _narrows.count; | |
| 71 | ||
| 72 | variables: Collections.Iterable[Symbol] => _narrows.keys; | |
| 73 | ||
| 74 | contains(v: Symbol) -> bool => _narrows.contains_key(v); | |
| 75 | ||
| 76 | // The narrowed type recorded for `v`, or null when `v` is | |
| 77 | // not narrowed in this environment. | |
| 78 | narrowed_type_of(v: Symbol) -> Type? is | |
| 79 | let result: Type mut; | |
| 80 | ||
| 81 | if _narrows.try_get_value(v, result ref) then | |
| 82 | return result; | |
| 83 | fi | |
| 84 | ||
| 85 | return null; | |
| 86 | si | |
| 87 | ||
| 88 | // Record `v` as narrowed to `t` (mutating). A bottom env | |
| 89 | // ignores narrows — it stays unreachable. | |
| 90 | // | |
| 91 | // If `v` already carries a narrow `existing`, compose: | |
| 92 | // `INTERSECTION.try_create(existing, t)`. The factory: | |
| 93 | // - returns `t` when t strict-subtypes existing (refining), | |
| 94 | // - returns `existing` when existing strict-subtypes t (the | |
| 95 | // new narrow is weaker, no-op), | |
| 96 | // - returns a multi-member intersection when both are | |
| 97 | // real new facts (e.g., a class plus a sibling trait), | |
| 98 | // - returns null when the two carry unrelated concrete | |
| 99 | // identities — no runtime value can be both, so the edge | |
| 100 | // recording the narrow is statically impossible. The code | |
| 101 | // on that edge is written against the newly tested type | |
| 102 | // (`elif isa TUPLE(x) then x.elements`), so `t` replaces | |
| 103 | // the stale narrow: on an unreachable edge any view is | |
| 104 | // sound, and the tested type is the one that typechecks. | |
| 105 | // So stacked narrows like `if isa A(x) then if isa B(x)` | |
| 106 | // produce `Declared & A & B` rather than dropping A. | |
| 107 | // | |
| 108 | // Skipped when composing with an existing narrow doesn't | |
| 109 | // change the recorded type — every extra fact costs | |
| 110 | // downstream copies, joins and kill iterations for no | |
| 111 | // observable effect. A fresh record (no existing narrow) is | |
| 112 | // always kept; if it turns out to no-op against v's declared | |
| 113 | // type, the branch-entry `_apply_one` catches it. | |
| 114 | set_narrow(v: Symbol, t: Type) is | |
| 115 | if is_bottom then | |
| 116 | return; | |
| 117 | fi | |
| 118 | ||
| 119 | let existing: Type mut; | |
| 120 | ||
| 121 | if _narrows.try_get_value(v, existing ref) then | |
| 122 | let composed = INTERSECTION.try_create(existing, t); | |
| 123 | ||
| 124 | if !composed? then | |
| 125 | _narrows[v] = t; | |
| 126 | return; | |
| 127 | fi | |
| 128 | ||
| 129 | if composed.matches(existing) then | |
| 130 | return; | |
| 131 | fi | |
| 132 | ||
| 133 | _narrows[v] = composed; | |
| 134 | else | |
| 135 | _narrows[v] = t; | |
| 136 | fi | |
| 137 | si | |
| 138 | ||
| 139 | // Record `t` as the narrow for `v`, discarding any existing | |
| 140 | // narrow instead of composing with it. For callers that have | |
| 141 | // already computed the absolute narrowed type — the else-edge | |
| 142 | // complement is derived from the current narrow, so it fully | |
| 143 | // supersedes it. Composition would be wrong when the complement | |
| 144 | // collapses to a supertype of the prior narrow (a concrete root | |
| 145 | // that outlives every eliminated subclass): INTERSECTION would | |
| 146 | // reinstate the wider prior narrow and the eliminated subclass | |
| 147 | // would survive. | |
| 148 | replace_narrow(v: Symbol, t: Type) is | |
| 149 | if is_bottom then | |
| 150 | return; | |
| 151 | fi | |
| 152 | ||
| 153 | _narrows[v] = t; | |
| 154 | si | |
| 155 | ||
| 156 | // Path-keyed mirror of `replace_narrow`. | |
| 157 | replace_path_narrow(path: ACCESS_PATH, t: Type) is | |
| 158 | if is_bottom then | |
| 159 | return; | |
| 160 | fi | |
| 161 | ||
| 162 | _path_narrows[path] = t; | |
| 163 | si | |
| 164 | ||
| 165 | // Forget any narrow for `v` (mutating) — used by the | |
| 166 | // assignment transfer function. | |
| 167 | drop_narrow(v: Symbol) is | |
| 168 | if _narrows.contains_key(v) then | |
| 169 | _narrows.remove(v); | |
| 170 | fi | |
| 171 | si | |
| 172 | ||
| 173 | // The locals definitely assigned at this point. | |
| 174 | assigned_variables: Collections.Iterable[Symbol] => _assigned; | |
| 175 | ||
| 176 | // True iff `v` is definitely assigned at this point. | |
| 177 | is_assigned(v: Symbol) -> bool => _assigned.contains(v); | |
| 178 | ||
| 179 | // Record `v` as definitely assigned (mutating). A bottom env | |
| 180 | // ignores it — it stays unreachable. | |
| 181 | set_assigned(v: Symbol) is | |
| 182 | if is_bottom then | |
| 183 | return; | |
| 184 | fi | |
| 185 | ||
| 186 | _assigned.add(v); | |
| 187 | si | |
| 188 | ||
| 189 | // The locals known to hold a value at this point. | |
| 190 | non_null_variables: Collections.Iterable[Symbol] => _non_null; | |
| 191 | ||
| 192 | // True iff `v` is known to hold a value at this point. | |
| 193 | is_non_null(v: Symbol) -> bool => _non_null.contains(v); | |
| 194 | ||
| 195 | // Record `v` as known to hold a value (mutating). A bottom | |
| 196 | // env ignores it — it stays unreachable. | |
| 197 | // | |
| 198 | // Callers should filter out presence facts on non-optional | |
| 199 | // targets themselves: NARROW_ENV can't safely check `v.type` | |
| 200 | // here because the symbol's live type reflects whatever the | |
| 201 | // outer walk state applied, not the fresh env being built — | |
| 202 | // a redundant-looking fact recorded on a nested if body may | |
| 203 | // still be observable at the branch entry when the outer | |
| 204 | // narrow is restored. | |
| 205 | set_non_null(v: Symbol) is | |
| 206 | if is_bottom then | |
| 207 | return; | |
| 208 | fi | |
| 209 | ||
| 210 | _non_null.add(v); | |
| 211 | si | |
| 212 | ||
| 213 | // Forget that `v` is known to hold a value (mutating) — used | |
| 214 | // by the assignment transfer function. | |
| 215 | drop_non_null(v: Symbol) is | |
| 216 | if _non_null.contains(v) then | |
| 217 | _non_null.remove(v); | |
| 218 | fi | |
| 219 | si | |
| 220 | ||
| 221 | // The member-access paths known to hold a value at this point. | |
| 222 | non_null_paths: Collections.Iterable[ACCESS_PATH] => _non_null_paths; | |
| 223 | ||
| 224 | // True iff `path` is known to hold a value at this point. | |
| 225 | is_non_null_path(path: ACCESS_PATH) -> bool => _non_null_paths.contains(path); | |
| 226 | ||
| 227 | // Record `path` as known to hold a value (mutating). A bottom | |
| 228 | // env ignores it — it stays unreachable. | |
| 229 | set_non_null_path(path: ACCESS_PATH) is | |
| 230 | if is_bottom then | |
| 231 | return; | |
| 232 | fi | |
| 233 | ||
| 234 | _non_null_paths.add(path); | |
| 235 | si | |
| 236 | ||
| 237 | // The member-access paths carrying a type narrow at this point. | |
| 238 | narrowed_paths: Collections.Iterable[ACCESS_PATH] => _path_narrows.keys; | |
| 239 | ||
| 240 | // The narrowed type recorded for `path`, or null when it is | |
| 241 | // not narrowed in this environment. | |
| 242 | narrowed_type_of_path(path: ACCESS_PATH) -> Type? is | |
| 243 | let result: Type mut; | |
| 244 | ||
| 245 | if _path_narrows.try_get_value(path, result ref) then | |
| 246 | return result; | |
| 247 | fi | |
| 248 | ||
| 249 | return null; | |
| 250 | si | |
| 251 | ||
| 252 | // Record `path` as narrowed to `t` (mutating). Bottom env | |
| 253 | // ignores it. Stacks like `set_narrow` — a prior narrow on | |
| 254 | // the same path composes with `t` via INTERSECTION, and an | |
| 255 | // unrelated-concretes pair (statically-impossible test edge) | |
| 256 | // replaces the stale narrow with `t` for the same reason. | |
| 257 | set_path_narrow(path: ACCESS_PATH, t: Type) is | |
| 258 | if is_bottom then | |
| 259 | return; | |
| 260 | fi | |
| 261 | ||
| 262 | let existing: Type mut; | |
| 263 | ||
| 264 | if _path_narrows.try_get_value(path, existing ref) then | |
| 265 | let composed = INTERSECTION.try_create(existing, t); | |
| 266 | ||
| 267 | _path_narrows[path] = if composed? then composed else t fi; | |
| 268 | else | |
| 269 | _path_narrows[path] = t; | |
| 270 | fi | |
| 271 | si | |
| 272 | ||
| 273 | // Forget every tracked path — the call transfer: a | |
| 274 | // possibly-storing callee may have changed anything a path | |
| 275 | // reads. Same reasoning for path type narrows. | |
| 276 | drop_all_paths() is | |
| 277 | _non_null_paths.clear(); | |
| 278 | _path_narrows.clear(); | |
| 279 | si | |
| 280 | ||
| 281 | // Forget every path that reads through a property getter — | |
| 282 | // the heap-store transfer: a store anywhere can change what a | |
| 283 | // getter returns. Fields-only paths survive; a store to a | |
| 284 | // field they read through is handled by drop_paths_through. | |
| 285 | // Applies to both presence and type-narrow slots. | |
| 286 | drop_getter_paths() is | |
| 287 | let doomed = Collections.LIST[ACCESS_PATH](); | |
| 288 | ||
| 289 | for p in _non_null_paths do | |
| 290 | if p.has_getter_hop then | |
| 291 | doomed.add(p); | |
| 292 | fi | |
| 293 | od | |
| 294 | ||
| 295 | for p in doomed do | |
| 296 | _non_null_paths.remove(p); | |
| 297 | od | |
| 298 | ||
| 299 | let doomed_narrows = Collections.LIST[ACCESS_PATH](); | |
| 300 | ||
| 301 | for p in _path_narrows.keys do | |
| 302 | if p.has_getter_hop then | |
| 303 | doomed_narrows.add(p); | |
| 304 | fi | |
| 305 | od | |
| 306 | ||
| 307 | for p in doomed_narrows do | |
| 308 | _path_narrows.remove(p); | |
| 309 | od | |
| 310 | si | |
| 311 | ||
| 312 | // Forget every path that reads through `member` at any hop — | |
| 313 | // the member-store transfer. Keyed on the member symbol, not | |
| 314 | // the written receiver, so a store through an aliased | |
| 315 | // receiver still invalidates. Applies to both presence and | |
| 316 | // type-narrow slots. | |
| 317 | drop_paths_through(member: Symbol) is | |
| 318 | let doomed = Collections.LIST[ACCESS_PATH](); | |
| 319 | ||
| 320 | for p in _non_null_paths do | |
| 321 | if p.contains_member(member) then | |
| 322 | doomed.add(p); | |
| 323 | fi | |
| 324 | od | |
| 325 | ||
| 326 | for p in doomed do | |
| 327 | _non_null_paths.remove(p); | |
| 328 | od | |
| 329 | ||
| 330 | let doomed_narrows = Collections.LIST[ACCESS_PATH](); | |
| 331 | ||
| 332 | for p in _path_narrows.keys do | |
| 333 | if p.contains_member(member) then | |
| 334 | doomed_narrows.add(p); | |
| 335 | fi | |
| 336 | od | |
| 337 | ||
| 338 | for p in doomed_narrows do | |
| 339 | _path_narrows.remove(p); | |
| 340 | od | |
| 341 | si | |
| 342 | ||
| 343 | // Forget every tracked path rooted at `root` — used when the | |
| 344 | // root is reassigned, which redirects every `root.…` path. | |
| 345 | // Applies to both presence and type-narrow slots. | |
| 346 | drop_paths_rooted_at(root: Symbol) is | |
| 347 | let doomed = Collections.LIST[ACCESS_PATH](); | |
| 348 | ||
| 349 | for p in _non_null_paths do | |
| 350 | if p.root == root then | |
| 351 | doomed.add(p); | |
| 352 | fi | |
| 353 | od | |
| 354 | ||
| 355 | for p in doomed do | |
| 356 | _non_null_paths.remove(p); | |
| 357 | od | |
| 358 | ||
| 359 | let doomed_narrows = Collections.LIST[ACCESS_PATH](); | |
| 360 | ||
| 361 | for p in _path_narrows.keys do | |
| 362 | if p.root == root then | |
| 363 | doomed_narrows.add(p); | |
| 364 | fi | |
| 365 | od | |
| 366 | ||
| 367 | for p in doomed_narrows do | |
| 368 | _path_narrows.remove(p); | |
| 369 | od | |
| 370 | si | |
| 371 | ||
| 372 | // Forget every fact a heap mutation can invalidate: narrows | |
| 373 | // and presence facts keyed on fields or properties, and every | |
| 374 | // member-access path. Local-variable facts survive — a callee | |
| 375 | // cannot reach a local. Used by controlled walks whose branch | |
| 376 | // environments derive from a snapshot taken before the walk: | |
| 377 | // when the walk killed heap facts, the snapshot's heap facts | |
| 378 | // cannot be trusted on the edges built from it. | |
| 379 | drop_heap_facts() is | |
| 380 | let stale = Collections.LIST[Symbol](); | |
| 381 | ||
| 382 | for v in _narrows.keys do | |
| 383 | if isa Semantic.Symbols.Field(v) \/ isa Semantic.Symbols.Property(v) then | |
| 384 | stale.add(v); | |
| 385 | fi | |
| 386 | od | |
| 387 | ||
| 388 | for v in stale do | |
| 389 | _narrows.remove(v); | |
| 390 | od | |
| 391 | ||
| 392 | let stale_presence = Collections.LIST[Symbol](); | |
| 393 | ||
| 394 | for v in _non_null do | |
| 395 | if isa Semantic.Symbols.Field(v) \/ isa Semantic.Symbols.Property(v) then | |
| 396 | stale_presence.add(v); | |
| 397 | fi | |
| 398 | od | |
| 399 | ||
| 400 | for v in stale_presence do | |
| 401 | _non_null.remove(v); | |
| 402 | od | |
| 403 | ||
| 404 | _non_null_paths.clear(); | |
| 405 | _path_narrows.clear(); | |
| 406 | si | |
| 407 | ||
| 408 | copy() -> NARROW_ENV is | |
| 409 | let e = NARROW_ENV(); | |
| 410 | e.is_bottom = is_bottom; | |
| 411 | ||
| 412 | for v in _narrows.keys do | |
| 413 | e._narrows[v] = _narrows[v]; | |
| 414 | od | |
| 415 | ||
| 416 | for v in _assigned do | |
| 417 | e._assigned.add(v); | |
| 418 | od | |
| 419 | ||
| 420 | for v in _non_null do | |
| 421 | e._non_null.add(v); | |
| 422 | od | |
| 423 | ||
| 424 | for p in _non_null_paths do | |
| 425 | e._non_null_paths.add(p); | |
| 426 | od | |
| 427 | ||
| 428 | for p in _path_narrows.keys do | |
| 429 | e._path_narrows[p] = _path_narrows[p]; | |
| 430 | od | |
| 431 | ||
| 432 | return e; | |
| 433 | si | |
| 434 | ||
| 435 | // A copy carrying only the definite-assignment facts — no | |
| 436 | // narrows, reachable. Used where the narrowing facts must be | |
| 437 | // discarded conservatively (after a try statement) but | |
| 438 | // assignments made before it still hold. | |
| 439 | with_only_assigned() -> NARROW_ENV is | |
| 440 | let e = NARROW_ENV(); | |
| 441 | ||
| 442 | for v in _assigned do | |
| 443 | e._assigned.add(v); | |
| 444 | od | |
| 445 | ||
| 446 | return e; | |
| 447 | si | |
| 448 | ||
| 449 | // Merge two environments at a control-flow merge point. | |
| 450 | // `bottom` is the identity (a diverging branch contributes | |
| 451 | // nothing). Every domain merges by intersection: a variable | |
| 452 | // survives the narrowing merge only when narrowed in BOTH | |
| 453 | // inputs (merged type = least upper bound); a variable is | |
| 454 | // definitely assigned after the merge only when assigned in | |
| 455 | // BOTH inputs; likewise known-non-null only when in both. | |
| 456 | join(a: NARROW_ENV, b: NARROW_ENV) -> NARROW_ENV static is | |
| 457 | if a.is_bottom then | |
| 458 | return b.copy(); | |
| 459 | fi | |
| 460 | ||
| 461 | if b.is_bottom then | |
| 462 | return a.copy(); | |
| 463 | fi | |
| 464 | ||
| 465 | let result = NARROW_ENV(); | |
| 466 | ||
| 467 | for v in a.variables do | |
| 468 | if let ta = a.narrowed_type_of(v), tb = b.narrowed_type_of(v) then | |
| 469 | // Two narrows over the same closed root join by | |
| 470 | // subtype-set union — exact, and it keeps the | |
| 471 | // optional flag when either edge can be null. | |
| 472 | // The general LUB is the fallback for every | |
| 473 | // other shape. | |
| 474 | let merged mut = Semantic.Types.ONE_OF.try_join(ta, tb); | |
| 475 | ||
| 476 | if !merged? then | |
| 477 | let lub = Semantic.LEAST_UPPER_BOUND_MAP(); | |
| 478 | lub.add(ta); | |
| 479 | lub.add(tb); | |
| 480 | ||
| 481 | merged = lub.get_result(); | |
| 482 | fi | |
| 483 | ||
| 484 | if merged? then | |
| 485 | result.set_narrow(v, merged); | |
| 486 | fi | |
| 487 | fi | |
| 488 | od | |
| 489 | ||
| 490 | for v in a.assigned_variables do | |
| 491 | if b.is_assigned(v) then | |
| 492 | result.set_assigned(v); | |
| 493 | fi | |
| 494 | od | |
| 495 | ||
| 496 | for v in a.non_null_variables do | |
| 497 | if b.is_non_null(v) then | |
| 498 | result.set_non_null(v); | |
| 499 | fi | |
| 500 | od | |
| 501 | ||
| 502 | for p in a.non_null_paths do | |
| 503 | if b.is_non_null_path(p) then | |
| 504 | result.set_non_null_path(p); | |
| 505 | fi | |
| 506 | od | |
| 507 | ||
| 508 | for p in a.narrowed_paths do | |
| 509 | if let ta = a.narrowed_type_of_path(p), tb = b.narrowed_type_of_path(p) then | |
| 510 | // Two narrows over the same closed root join by | |
| 511 | // subtype-set union — mirrors the symbol case. | |
| 512 | let merged mut = Semantic.Types.ONE_OF.try_join(ta, tb); | |
| 513 | ||
| 514 | if !merged? then | |
| 515 | let lub = Semantic.LEAST_UPPER_BOUND_MAP(); | |
| 516 | lub.add(ta); | |
| 517 | lub.add(tb); | |
| 518 | ||
| 519 | merged = lub.get_result(); | |
| 520 | fi | |
| 521 | ||
| 522 | if merged? then | |
| 523 | result.set_path_narrow(p, merged); | |
| 524 | fi | |
| 525 | fi | |
| 526 | od | |
| 527 | ||
| 528 | return result; | |
| 529 | si | |
| 530 | si | |
| 531 | si |