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| 1 | namespace Semantic is | |
| 2 | use System.Exception | |
| 3 | ||
| 4 | use Ghul.Pipes | |
| 5 | ||
| 6 | use Logging | |
| 7 | use Source | |
| 8 | ||
| 9 | use Types.Type | |
| 10 | ||
| 11 | // `score` is the summed per-argument match quality, kept for | |
| 12 | // ranking candidates against each other. `needs_retry` is the | |
| 13 | // explicit signal that a function-literal actual with implicit | |
| 14 | // parameter types matched without its real signature, so a | |
| 15 | // constraint-push re-walk of the arguments could improve the | |
| 16 | // result. Callers must consult `needs_retry` rather than testing | |
| 17 | // `score` against a MATCH constant: the sum of several coercion | |
| 18 | // scores can collide with any single MATCH value. | |
| 19 | class OVERLOAD_RESOLVE_RESULT(function: Symbols.Function, score: Types.MATCH, needs_retry: bool) is | |
| 20 | si | |
| 21 | ||
| 22 | class OVERLOAD_MATCHES_RESULT( | |
| 23 | results: Collections.List[Symbols.Function], | |
| 24 | best_result_index: int, | |
| 25 | current_parameter_index: int public | |
| 26 | ) is | |
| 27 | si | |
| 28 | ||
| 29 | class OVERLOAD_RESOLVER(_logger: Logger) is | |
| 30 | match_propagator: MATCH_PROPAGATOR public | |
| 31 | _callee_parameter_slot: CALLEE_PARAMETER_SLOT | |
| 32 | _delegate_shape: DELEGATE_SHAPE | |
| 33 | ||
| 34 | super() | |
| 35 | ||
| 36 | init(..) is | |
| 37 | match_propagator = MATCH_PROPAGATOR(_logger) | |
| 38 | _callee_parameter_slot = CALLEE_PARAMETER_SLOT() | |
| 39 | _delegate_shape = DELEGATE_SHAPE() | |
| 40 | si | |
| 41 | ||
| 42 | resolve( | |
| 43 | location: LOCATION, | |
| 44 | group: Symbols.FUNCTION_GROUP, | |
| 45 | arguments: Collections.List[Type], | |
| 46 | want_infer: bool, | |
| 47 | want_instance: bool, | |
| 48 | is_constructor_call: bool | |
| 49 | ) -> OVERLOAD_RESOLVE_RESULT? => | |
| 50 | resolve(location, group, arguments, want_infer, want_instance, is_constructor_call, null, null) | |
| 51 | ||
| 52 | // `restrict_to`, when non-null, limits resolution to the given | |
| 53 | // candidates instead of the whole group - used by named- | |
| 54 | // argument calls, which have already culled the group to the | |
| 55 | // overloads whose parameter names match. | |
| 56 | resolve( | |
| 57 | location: LOCATION, | |
| 58 | group: Symbols.FUNCTION_GROUP, | |
| 59 | arguments: Collections.List[Type], | |
| 60 | want_infer: bool, | |
| 61 | want_instance: bool, | |
| 62 | is_constructor_call: bool, | |
| 63 | restrict_to: Collections.List[Symbols.Function]? | |
| 64 | ) -> OVERLOAD_RESOLVE_RESULT? => | |
| 65 | resolve(location, group, arguments, want_infer, want_instance, is_constructor_call, restrict_to, null) | |
| 66 | ||
| 67 | // `return_constraint`, when non-null, supplies the return-type | |
| 68 | // context (typically `function.return_type` of the enclosing | |
| 69 | // function for a call in return-position, or the LHS slot type | |
| 70 | // for an assignment-position call). Used as a tie-breaker when | |
| 71 | // arg-side scoring leaves multiple candidates tied: a candidate | |
| 72 | // whose return type is assignable to the constraint wins over | |
| 73 | // one that isn't. | |
| 74 | resolve( | |
| 75 | location: LOCATION, | |
| 76 | group: Symbols.FUNCTION_GROUP, | |
| 77 | arguments: Collections.List[Type], | |
| 78 | want_infer: bool, | |
| 79 | want_instance: bool, | |
| 80 | is_constructor_call: bool, | |
| 81 | restrict_to: Collections.List[Symbols.Function]?, | |
| 82 | return_constraint: Type? | |
| 83 | ) -> OVERLOAD_RESOLVE_RESULT? | |
| 84 | is | |
| 85 | let mark = _logger.mark() | |
| 86 | ||
| 87 | try | |
| 88 | return _resolve(location, group, arguments, want_infer, want_instance, is_constructor_call, restrict_to, return_constraint) | |
| 89 | catch e: Exception | |
| 90 | _logger.release(mark) | |
| 91 | ||
| 92 | _logger.exception(location, e, "exception resolving overload: {group} arguments {arguments}") | |
| 93 | return null | |
| 94 | ||
| 95 | finally | |
| 96 | _logger.release(mark) | |
| 97 | yrt | |
| 98 | si | |
| 99 | ||
| 100 | find_matches( | |
| 101 | group: Symbols.FUNCTION_GROUP, | |
| 102 | arguments: Collections.List[Type] | |
| 103 | ) -> OVERLOAD_MATCHES_RESULT? | |
| 104 | is | |
| 105 | let mark = _logger.mark() | |
| 106 | ||
| 107 | try | |
| 108 | return _find_matches(group, arguments) | |
| 109 | catch e: Exception | |
| 110 | _logger.release(mark) | |
| 111 | ||
| 112 | _logger.exception(group.location, e, "exception resolving overload: {group} arguments {arguments}") | |
| 113 | return null | |
| 114 | ||
| 115 | finally | |
| 116 | _logger.release(mark) | |
| 117 | yrt | |
| 118 | si | |
| 119 | ||
| 120 | _resolve( | |
| 121 | location: LOCATION, | |
| 122 | group: Symbols.FUNCTION_GROUP, | |
| 123 | arguments: Collections.List[Type], | |
| 124 | want_infer: bool, | |
| 125 | want_instance: bool, | |
| 126 | is_constructor_call: bool, | |
| 127 | restrict_to: Collections.List[Symbols.Function]?, | |
| 128 | return_constraint: Type? | |
| 129 | ) -> OVERLOAD_RESOLVE_RESULT? | |
| 130 | is | |
| 131 | // FIXME: this could just as well be applied to any parameters of generic type, not just anon functions | |
| 132 | // an argument entry may be null | |
| 133 | @suppress("presence-test-non-optional") | |
| 134 | let needs_second_call = arguments |> any(a => a? /\ a.is_function_with_any_implicit_argument_types) | |
| 135 | ||
| 136 | let saw_delegate_target mut = false | |
| 137 | ||
| 138 | let is_ambiguous mut = false | |
| 139 | ||
| 140 | let best_score mut = cast int (Types.MATCH.DIFFERENT) | |
| 141 | let result: Symbols.Function? mut = _ | |
| 142 | ||
| 143 | let ambiguous_matches: Collections.LIST[Symbols.Function]? mut = null | |
| 144 | ||
| 145 | let search_functions = if restrict_to? then restrict_to else group.functions fi | |
| 146 | ||
| 147 | // A static constructor is invoked by the CLR, never by an | |
| 148 | // explicit call or `T(...)` construction, so it must not be | |
| 149 | // an overload candidate even though it shares the `init` | |
| 150 | // group with the instance constructors. | |
| 151 | let functions_to_search = search_functions |> filter(f => (want_instance \/ !f.is_instance) /\ !f.is_static_constructor) | |
| 152 | ||
| 153 | // Whether more than one candidate takes this many arguments. A | |
| 154 | // delegate the argument cannot become only decides between | |
| 155 | // candidates; against a lone candidate the conversion is left to | |
| 156 | // fail where it is made, which says more about why. | |
| 157 | let has_rivals = (functions_to_search |> filter(f => f.arguments.count == arguments.count) |> count()) > 1 | |
| 158 | ||
| 159 | // Per candidate that bound any type argument, what it bound. | |
| 160 | // Kept rather than acted on: the bindings are offered to a | |
| 161 | // placeholder actual once the winner is known, since | |
| 162 | // ranking visits every candidate that scores at least as | |
| 163 | // well as the best so far. | |
| 164 | let candidate_bindings = Collections.LIST[(candidate: Symbols.Function, bindings: Types.GENERIC_ARGUMENT_BIND_RESULTS)]() | |
| 165 | ||
| 166 | // We need to return PARTIAL if any actual argument types are wild. 'PARTIAL' provides | |
| 167 | // the caller with the best match we can find, and the caller is expected to use that | |
| 168 | // to bind any unknown types in the actual arguments and then try overload resolution | |
| 169 | // again | |
| 170 | ||
| 171 | for f in functions_to_search do | |
| 172 | let actual: Symbols.Function? mut = f | |
| 173 | ||
| 174 | // A candidate with no formals and nothing to bind is the | |
| 175 | // answer as soon as it is found: ranking has no argument | |
| 176 | // to compare and no type parameter to pin from the call | |
| 177 | // site, so it can only put a group holding the same | |
| 178 | // member redeclared along two inherited paths - which | |
| 179 | // member lookup answers, not overload resolution - to a | |
| 180 | // tie it cannot break. A generic one does have something | |
| 181 | // to pin, from the type the call site expects, so it | |
| 182 | // takes the ordinary path. | |
| 183 | if f.arguments.count == 0 /\ arguments.count == 0 /\ !f.is_generic then | |
| 184 | return OVERLOAD_RESOLVE_RESULT(f, Types.MATCH.SAME, false) | |
| 185 | elif f.arguments.count == arguments.count then | |
| 186 | let want_try_bind_owner_generic_arguments mut = false | |
| 187 | let want_try_bind_function_generic_arguments mut = false | |
| 188 | ||
| 189 | if is_constructor_call then | |
| 190 | want_try_bind_owner_generic_arguments = true | |
| 191 | want_try_bind_function_generic_arguments = false | |
| 192 | elif f.is_instance then | |
| 193 | // Iterative-inference: an instance method's | |
| 194 | // owner type-args may be unbound when the | |
| 195 | // receiver was constructed without explicit | |
| 196 | // type-args and without args binding T (e.g. | |
| 197 | // `let m = Box(); m.set(42)`). Allow owner- | |
| 198 | // generic-arg binding here so the resolver can | |
| 199 | // pick T = int from the actual argument and | |
| 200 | // produce the specialized owner. For receivers | |
| 201 | // whose type-args are already bound, the | |
| 202 | // specialization is a no-op. | |
| 203 | want_try_bind_owner_generic_arguments = true | |
| 204 | want_try_bind_function_generic_arguments = true | |
| 205 | elif f.is_generic then | |
| 206 | want_try_bind_owner_generic_arguments = true | |
| 207 | want_try_bind_function_generic_arguments = true | |
| 208 | else | |
| 209 | want_try_bind_owner_generic_arguments = true | |
| 210 | want_try_bind_function_generic_arguments = false | |
| 211 | fi | |
| 212 | ||
| 213 | let try_bind_generic_arguments mut = false | |
| 214 | let score mut = cast int(Types.MATCH.SAME) | |
| 215 | ||
| 216 | // A global function's owner is a namespace, not a | |
| 217 | // Classy, so this cast is null whenever | |
| 218 | // want_try_bind_owner_generic_arguments will never | |
| 219 | // find owner bindings to act on below. Left | |
| 220 | // optional and unwrapped only at the two call sites | |
| 221 | // that are reachable exclusively through a | |
| 222 | // successful owner binding, which cannot happen | |
| 223 | // for a non-Classy owner. | |
| 224 | let owner_symbol = cast Symbols.Classy?(f.owner) | |
| 225 | ||
| 226 | for i in 0..f.arguments.count do | |
| 227 | let match: Types.MATCH mut | |
| 228 | ||
| 229 | let f_arg = f.arguments[i] | |
| 230 | let arg = arguments[i] | |
| 231 | ||
| 232 | // an argument may be null | |
| 233 | @suppress("presence-test-non-optional") | |
| 234 | if arg? then | |
| 235 | match = f_arg.compare(arg) | |
| 236 | ||
| 237 | // A function literal can be compiled as the | |
| 238 | // delegate this formal asks for, but it has | |
| 239 | // been walked as a plain function type and so | |
| 240 | // compares DIFFERENT. Report a partial match | |
| 241 | // instead: the retry pass pushes this formal | |
| 242 | // down and re-walks the argument, which either | |
| 243 | // produces the delegate or fails the second | |
| 244 | // resolve on its own terms. | |
| 245 | // A literal whose parameter count differs from | |
| 246 | // the delegate's can never become it, so where | |
| 247 | // another overload competes this one is no | |
| 248 | // candidate at all. | |
| 249 | if | |
| 250 | match == Types.MATCH.DIFFERENT /\ | |
| 251 | arg.is_function /\ | |
| 252 | _delegate_shape.is_named_delegate(f_arg, IoC.CONTAINER.instance.innate_symbol_lookup) /\ | |
| 253 | (!has_rivals \/ _delegate_shape.could_take_arity(f_arg, ARGUMENT_PACK.parameter_count(arg), IoC.CONTAINER.instance.innate_symbol_lookup)) | |
| 254 | then | |
| 255 | match = Types.MATCH.PARTIAL | |
| 256 | saw_delegate_target = true | |
| 257 | fi | |
| 258 | ||
| 259 | if match == Types.MATCH.DIFFERENT then | |
| 260 | // if any argument type compare returns DIFFERENT then | |
| 261 | // this overload cannot match the supplied arguments | |
| 262 | // even allowing for type argument inference of any | |
| 263 | // type arguments in the formal arguments or of | |
| 264 | // unknown types in the actual arguments, so | |
| 265 | // bail on this overload immediately: | |
| 266 | score = cast int(Types.MATCH.DIFFERENT) | |
| 267 | break | |
| 268 | elif match == Types.MATCH.WILD then | |
| 269 | // either or both of the following has occurred: | |
| 270 | // 1. the formal argument type is 'wild', i.e. its type expression | |
| 271 | // includes at least one generic type argument that could be free | |
| 272 | // to be bound to the type in corresponding position in the actual | |
| 273 | // argument type. The type argument could be appear inside the type | |
| 274 | // expression at any depth, for example `List[T]` or `int -> T` | |
| 275 | // 2. the actual argument type is 'any', i.e. its type expression | |
| 276 | // includes at least one unknown type where the actual type can | |
| 277 | // potentially be inferred based on the formal argument type | |
| 278 | ||
| 279 | // we need first to figure out which it is. If it's both then type | |
| 280 | // inference probably isn't possible, but we will still attempt it | |
| 281 | ||
| 282 | if f_arg.is_wild then | |
| 283 | // this formal argument is wild, we need to figure out if any | |
| 284 | // type arguments in it could be free in this context | |
| 285 | ||
| 286 | // if the overload is an instance method we then can't supply | |
| 287 | // actual type parameters to its owning class/struct either explicitly | |
| 288 | // or via inference - they're already applied to the instance we're | |
| 289 | // calling the method on | |
| 290 | ||
| 291 | // if the overload is a static method, we can potentially supply | |
| 292 | // actual type arguments for its owning class | |
| 293 | ||
| 294 | // and in either case we can supply actual type arguments for the | |
| 295 | // method itself | |
| 296 | ||
| 297 | // if the function is a global function then we can supply actual | |
| 298 | // type arguments for it | |
| 299 | ||
| 300 | // if the function is a constructor, and we're calling it for a | |
| 301 | // constructor expression, it cannot have generic arguments but | |
| 302 | // its owning type can, and we do want to supply them if we | |
| 303 | // can infer them from this overload | |
| 304 | ||
| 305 | match = Types.MATCH.SAME | |
| 306 | ||
| 307 | try_bind_generic_arguments = true | |
| 308 | else | |
| 309 | // Only the actual is wild: it names a type | |
| 310 | // variable of some enclosing declaration, which | |
| 311 | // is fixed where the call is written rather than | |
| 312 | // free to be bound by it. A formal that genuinely | |
| 313 | // accepts such a value - `object?`, or the | |
| 314 | // variable's own bound - has already compared | |
| 315 | // assignable through the ancestor walk, so | |
| 316 | // anything still reported wild here is a formal | |
| 317 | // the argument cannot satisfy under any | |
| 318 | // instantiation. | |
| 319 | score = cast int(Types.MATCH.DIFFERENT) | |
| 320 | break | |
| 321 | fi | |
| 322 | elif arg.is_error \/ arg.contains_inferred then | |
| 323 | // The actual argument is an ERROR/placeholder sentinel | |
| 324 | // or a composite carrying one inside. Treat as a | |
| 325 | // matching argument and see if that produces an | |
| 326 | // unambiguous overload result — if so the caller | |
| 327 | // uses the chosen overload's formal type to infer | |
| 328 | // back into the placeholder via match propagation. | |
| 329 | ||
| 330 | // FIXME not sure it makes sense to be setting score here - should be match | |
| 331 | score = cast int(Types.MATCH.PARTIAL) | |
| 332 | elif f_arg.is_wild /\ isa Types.NULL(arg) then | |
| 333 | // A wild optional formal (`T?`) trivially accepts a | |
| 334 | // bare null without pinning its type variable, so | |
| 335 | // compare returns a plain assignable match rather than | |
| 336 | // WILD. Still route through generic-argument binding: | |
| 337 | // the type variable is left free otherwise, and the | |
| 338 | // selected overload would emit with an unresolved `!!N` | |
| 339 | // that fails to load at run time. Errors and inference | |
| 340 | // sentinels are handled by the branch above; this is | |
| 341 | // only the genuine null literal. | |
| 342 | try_bind_generic_arguments = true | |
| 343 | elif | |
| 344 | is_constructor_call /\ | |
| 345 | f_arg.is_wild /\ | |
| 346 | owner_symbol? /\ | |
| 347 | owner_symbol.is_generic | |
| 348 | then | |
| 349 | // A constructor's formal can compare as an exact | |
| 350 | // match rather than wild when the actual is the | |
| 351 | // very type variable it mentions: `NODE(value)` | |
| 352 | // written inside `NODE[T]`, with `value: T`. That | |
| 353 | // `T` is the enclosing class's, fixed where the | |
| 354 | // call is written, and binding the class's type | |
| 355 | // arguments from it is still how the construction | |
| 356 | // gets its type, here `NODE[T]`. Without the | |
| 357 | // binding the open class's constructor is chosen, | |
| 358 | // and nothing ever pins its type argument. A | |
| 359 | // constructor of an already constructed type, | |
| 360 | // `NODE[T](value)`, has its type arguments and | |
| 361 | // nothing left to bind. | |
| 362 | try_bind_generic_arguments = true | |
| 363 | fi | |
| 364 | else | |
| 365 | // An actual or formal argument type is unresolved | |
| 366 | // (null) - reachable in analysis mode when an | |
| 367 | // expression's type has not yet been established. | |
| 368 | // Treat as a moderate-quality match so resolution | |
| 369 | // degrades gracefully instead of dereferencing null. | |
| 370 | match = Types.MATCH.ASSIGNABLE | |
| 371 | fi | |
| 372 | ||
| 373 | score = cast int(score) + cast int(match) | |
| 374 | od | |
| 375 | ||
| 376 | if try_bind_generic_arguments /\ score <= best_score /\ score < cast int(Types.MATCH.DIFFERENT) then | |
| 377 | // if we saw any generic argument types in any of the function formal argument types | |
| 378 | // then we need to try to bind them to concrete types from the corresponding actual | |
| 379 | // argument types | |
| 380 | ||
| 381 | let function_generic_argument_bindings = | |
| 382 | if want_try_bind_function_generic_arguments then | |
| 383 | f.try_bind_generic_arguments(location, arguments) | |
| 384 | else | |
| 385 | null | |
| 386 | fi | |
| 387 | ||
| 388 | let owner_generic_argument_bindings = | |
| 389 | if want_try_bind_owner_generic_arguments then | |
| 390 | f.try_bind_owner_generic_arguments(location, arguments) | |
| 391 | else | |
| 392 | null | |
| 393 | fi | |
| 394 | ||
| 395 | if let bindings = function_generic_argument_bindings ?? owner_generic_argument_bindings then | |
| 396 | candidate_bindings.add((candidate = f, bindings = bindings)) | |
| 397 | fi | |
| 398 | ||
| 399 | if function_generic_argument_bindings? then | |
| 400 | if function_generic_argument_bindings.is_bound then | |
| 401 | actual = f.specialize_function(function_generic_argument_bindings.map, null) | |
| 402 | elif needs_second_call then | |
| 403 | actual = f.specialize_function(function_generic_argument_bindings.map, null) | |
| 404 | score = cast int(Types.MATCH.PARTIAL) | |
| 405 | else | |
| 406 | score = cast int(Types.MATCH.DIFFERENT) | |
| 407 | fi | |
| 408 | elif owner_generic_argument_bindings? then | |
| 409 | if owner_generic_argument_bindings.is_bound then | |
| 410 | let specialized_owner = Symbols.GENERIC.try_create_from(location, owner_symbol!, owner_generic_argument_bindings.map) | |
| 411 | ||
| 412 | if specialized_owner? then | |
| 413 | actual = specialized_owner.find_specialized_function(f) | |
| 414 | else | |
| 415 | score = cast int(Types.MATCH.DIFFERENT) | |
| 416 | fi | |
| 417 | elif needs_second_call then | |
| 418 | let specialized_owner = Symbols.GENERIC.try_create_from(location, owner_symbol!, owner_generic_argument_bindings.map) | |
| 419 | ||
| 420 | if specialized_owner? then | |
| 421 | actual = specialized_owner.find_specialized_function(f) | |
| 422 | score = cast int(Types.MATCH.PARTIAL) | |
| 423 | else | |
| 424 | score = cast int(Types.MATCH.DIFFERENT) | |
| 425 | fi | |
| 426 | else | |
| 427 | score = cast int(Types.MATCH.DIFFERENT) | |
| 428 | fi | |
| 429 | else | |
| 430 | score = cast int(Types.MATCH.DIFFERENT) | |
| 431 | fi | |
| 432 | fi | |
| 433 | ||
| 434 | if score == best_score /\ score != cast int(Types.MATCH.DIFFERENT) /\ actual? then | |
| 435 | if !ambiguous_matches? then | |
| 436 | ambiguous_matches = Collections.LIST[Symbols.Function]() | |
| 437 | fi | |
| 438 | ||
| 439 | if ambiguous_matches.count == 0 /\ result? then | |
| 440 | ambiguous_matches.add(result) | |
| 441 | fi | |
| 442 | ||
| 443 | ambiguous_matches.add(actual) | |
| 444 | ||
| 445 | is_ambiguous = true | |
| 446 | elif score < best_score /\ actual? then | |
| 447 | if ambiguous_matches? then | |
| 448 | ambiguous_matches.clear() | |
| 449 | fi | |
| 450 | ||
| 451 | is_ambiguous = false | |
| 452 | best_score = score | |
| 453 | result = actual | |
| 454 | fi | |
| 455 | fi | |
| 456 | od | |
| 457 | ||
| 458 | // Every filter from here down picks a winner by comparing | |
| 459 | // what the candidates' formals look like against each | |
| 460 | // other - never against the actuals - so a tie is only | |
| 461 | // real information when the actuals themselves carried | |
| 462 | // some: an ambiguity formed purely because every actual is | |
| 463 | // still an unresolved placeholder (every formal compared | |
| 464 | // ASSIGNABLE against a sentinel) says nothing about which | |
| 465 | // candidate the call means, and picking one anyway commits | |
| 466 | // an arbitrary type as a constraint on the placeholder's | |
| 467 | // origin, which can permanently block a later, correct | |
| 468 | // constraint from ever being accepted. `can_rank` is the | |
| 469 | // same guard FORMAL_FIT_FILTER and CANDIDATE_SPECIFICITY | |
| 470 | // already apply below; reusing it here keeps every | |
| 471 | // tie-break in this chain agreeing on when a tie is worth | |
| 472 | // breaking at all. | |
| 473 | // | |
| 474 | // Left enabled for a `want_infer` caller: such a caller | |
| 475 | // reaches the "call is ambiguous" report a few lines below | |
| 476 | // when nothing here picks a winner, which is worse than an | |
| 477 | // arbitrary-but-harmless pick when that caller's own | |
| 478 | // top-level diagnostic already reports the real failure | |
| 479 | // once the placeholder never resolves. A `!want_infer` | |
| 480 | // caller instead declines silently and retries, which is | |
| 481 | // where committing an arbitrary constraint is unsound. | |
| 482 | let safe_to_narrow_tie = want_infer \/ CANDIDATE_SPECIFICITY.can_rank(arguments) | |
| 483 | ||
| 484 | if is_ambiguous /\ safe_to_narrow_tie then | |
| 485 | let non_object_matches = | |
| 486 | ambiguous_matches! |> | |
| 487 | filter(f => !(f.arguments |> any(a => a.is_object))) | |
| 488 | ||
| 489 | let count = non_object_matches |> count() | |
| 490 | ||
| 491 | if count == 1 then | |
| 492 | result = non_object_matches |> only() | |
| 493 | is_ambiguous = false | |
| 494 | elif count > 1 then | |
| 495 | ambiguous_matches = Collections.LIST(non_object_matches) | |
| 496 | fi | |
| 497 | fi | |
| 498 | ||
| 499 | // Return-type-context filter: when the caller supplied a | |
| 500 | // return-type constraint (e.g. a return statement whose | |
| 501 | // function returns `Tasks.TASK[int]`, or an assignment- | |
| 502 | // position call's LHS type), prefer candidates whose | |
| 503 | // return type is assignable to that constraint. Picks | |
| 504 | // between `from_exception(ex) -> Tasks.TASK` vs | |
| 505 | // `from_exception[T](ex) -> Tasks.TASK[T]` where T can | |
| 506 | // bind from the constraint — the latter is the | |
| 507 | // user's intent and the former would fail the return- | |
| 508 | // statement's own assignability check. Runs BEFORE the | |
| 509 | // non-generic filter so a generic candidate matching the | |
| 510 | // constraint wins over a non-generic one that doesn't. | |
| 511 | // | |
| 512 | // For a generic candidate whose return type carries type | |
| 513 | // variables that the constraint can pin (e.g. | |
| 514 | // `Tasks.TASK[T]` against `Tasks.TASK[int]`), specialize | |
| 515 | // the chosen function so its emitted return type binds T | |
| 516 | // from the constraint. Without this the caller would | |
| 517 | // accept the candidate as the right overload but reject | |
| 518 | // its result against the constraint at the next | |
| 519 | // assignability check. | |
| 520 | if is_ambiguous /\ safe_to_narrow_tie /\ return_constraint? /\ !return_constraint.is_sentinel then | |
| 521 | let constraint_matches = | |
| 522 | ambiguous_matches! |> | |
| 523 | filter(f => RETURN_CONSTRAINT_FILTER.matches(f, return_constraint)) | |
| 524 | ||
| 525 | let count = constraint_matches |> count() | |
| 526 | ||
| 527 | if count == 1 then | |
| 528 | result = constraint_matches |> only() | |
| 529 | is_ambiguous = false | |
| 530 | ||
| 531 | let specialized = RETURN_CONSTRAINT_FILTER.try_specialize(location, result, return_constraint) | |
| 532 | if specialized? then | |
| 533 | result = specialized | |
| 534 | fi | |
| 535 | elif count > 1 then | |
| 536 | ambiguous_matches = Collections.LIST(constraint_matches) | |
| 537 | fi | |
| 538 | fi | |
| 539 | ||
| 540 | if is_ambiguous /\ safe_to_narrow_tie then | |
| 541 | // Prefer non-generic candidates over function-generic | |
| 542 | // ones (concrete `<>(int, int)` beats specialized | |
| 543 | // `<>[T: struct](T, T)` for `int <> int`). A concrete | |
| 544 | // candidate has no `specialized_from` link AND no | |
| 545 | // function-level type-arguments; a specialized form | |
| 546 | // of a function-generic has `specialized_from` set. | |
| 547 | let non_generic_matches = | |
| 548 | ambiguous_matches! |> | |
| 549 | filter(f => | |
| 550 | !f.specialized_from? /\ | |
| 551 | f.generic_arguments.count == 0) | |
| 552 | ||
| 553 | let count = non_generic_matches |> count() | |
| 554 | ||
| 555 | if count == 1 then | |
| 556 | result = non_generic_matches |> only() | |
| 557 | is_ambiguous = false | |
| 558 | elif count > 1 then | |
| 559 | ambiguous_matches = Collections.LIST(non_generic_matches) | |
| 560 | fi | |
| 561 | fi | |
| 562 | ||
| 563 | // Then: prefer the candidate whose specialized formals fit | |
| 564 | // the actuals most closely. A formal carrying a free type | |
| 565 | // variable scored as an exact match above, before the | |
| 566 | // variable was bound, so candidates that fit quite | |
| 567 | // differently can arrive here tied. | |
| 568 | // | |
| 569 | // Runs below the filters above rather than beside them: | |
| 570 | // where a concrete candidate ties a generic one on score | |
| 571 | // it matched every actual exactly, so the two agree, and | |
| 572 | // this only has to speak where they have not. | |
| 573 | if is_ambiguous then | |
| 574 | let closest_matches = FORMAL_FIT_FILTER.pick(ambiguous_matches!, arguments) | |
| 575 | ||
| 576 | if closest_matches? then | |
| 577 | if closest_matches.count == 1 then | |
| 578 | result = closest_matches[0] | |
| 579 | is_ambiguous = false | |
| 580 | else | |
| 581 | ambiguous_matches = Collections.LIST(closest_matches) | |
| 582 | fi | |
| 583 | fi | |
| 584 | fi | |
| 585 | ||
| 586 | // Last: prefer the candidate whose formals sit furthest | |
| 587 | // down the inheritance graph, which is the one that | |
| 588 | // widened the actuals least. Runs after every filter | |
| 589 | // above, so it only ever sees ambiguities they left | |
| 590 | // unsettled - which are reported as errors otherwise. | |
| 591 | if is_ambiguous then | |
| 592 | let most_specific = CANDIDATE_SPECIFICITY.pick(ambiguous_matches!, arguments) | |
| 593 | ||
| 594 | if most_specific? then | |
| 595 | result = most_specific | |
| 596 | is_ambiguous = false | |
| 597 | fi | |
| 598 | fi | |
| 599 | ||
| 600 | if result? /\ !is_ambiguous then | |
| 601 | // A chosen candidate whose return type still carries | |
| 602 | // its own type parameter had nothing in the arguments | |
| 603 | // to bind it: `zero_of[T](n: int) -> T` mentions T | |
| 604 | // nowhere a supplied argument could pin it. The | |
| 605 | // call-site's return-type constraint is the only | |
| 606 | // remaining source, so bind from that when there is | |
| 607 | // one. Where there is not, the call is left carrying | |
| 608 | // the type parameter and whoever commits that type | |
| 609 | // reports it - resolution runs speculatively here, so | |
| 610 | // a diagnostic raised at this point would fire on | |
| 611 | // candidates the retry would have settled. | |
| 612 | let caller = IoC.CONTAINER.instance.symbol_table.current_function | |
| 613 | ||
| 614 | if | |
| 615 | result.return_type? /\ | |
| 616 | result.return_type.has_function_generic_argument_foreign_to(caller) | |
| 617 | then | |
| 618 | let specialized = | |
| 619 | if return_constraint? /\ !return_constraint.is_sentinel then | |
| 620 | RETURN_CONSTRAINT_FILTER.try_specialize(location, result, return_constraint) | |
| 621 | else | |
| 622 | null | |
| 623 | fi | |
| 624 | ||
| 625 | if specialized? then | |
| 626 | result = specialized | |
| 627 | fi | |
| 628 | fi | |
| 629 | ||
| 630 | // Back-feed the chosen overload's formal types as | |
| 631 | // constraints to any actual whose type is an | |
| 632 | // INFERRED_VARIABLE_TYPE placeholder. This is the | |
| 633 | // single primitive that drives iterative inference: | |
| 634 | // when a placeholder participates in overload | |
| 635 | // resolution and a concrete formal wins on the other | |
| 636 | // side, the formal becomes a constraint on the | |
| 637 | // placeholder's origin symbol. The retry loop in | |
| 638 | // COMPILE_EXPRESSIONS.visit(FUNCTION) then re-walks | |
| 639 | // the body with the narrowed type. Operators (which | |
| 640 | // are method calls in ghūl) flow through this path | |
| 641 | // for free. | |
| 642 | // Only now does the chosen candidate's binding reach a | |
| 643 | // placeholder actual. A candidate that bound cleanly and | |
| 644 | // then lost - on score, or on one of the tie-breaks | |
| 645 | // above - said nothing about what the call means, and | |
| 646 | // the lower bound it would have pushed is never | |
| 647 | // withdrawn. | |
| 648 | SELECTED_CANDIDATE_BINDINGS.offer(result, candidate_bindings) | |
| 649 | ||
| 650 | _propagate_chosen_match_args(result, arguments) | |
| 651 | ||
| 652 | if needs_second_call then | |
| 653 | best_score = cast int(Types.MATCH.PARTIAL) | |
| 654 | fi | |
| 655 | ||
| 656 | return OVERLOAD_RESOLVE_RESULT(result, cast Types.MATCH(best_score), needs_second_call \/ saw_delegate_target) | |
| 657 | fi | |
| 658 | ||
| 659 | if | |
| 660 | arguments |> any(a => a.is_error \/ (!want_infer /\ a.is_sentinel)) | |
| 661 | then | |
| 662 | return null | |
| 663 | fi | |
| 664 | ||
| 665 | let tried = Collections.LIST[Symbols.Function](20) | |
| 666 | ||
| 667 | for f in functions_to_search do | |
| 668 | // A candidate declaring an argument pack is one the call | |
| 669 | // may have meant with the pack spread out, whatever number | |
| 670 | // of arguments that came to, so it is worth showing. | |
| 671 | if f.arguments.count == arguments.count \/ _declares_argument_pack(f) then | |
| 672 | tried.add(f) | |
| 673 | fi | |
| 674 | od | |
| 675 | ||
| 676 | let maybe_static mut = "" | |
| 677 | ||
| 678 | if !want_instance then | |
| 679 | maybe_static = "static " | |
| 680 | fi | |
| 681 | ||
| 682 | if is_ambiguous then | |
| 683 | _logger.error( | |
| 684 | location, | |
| 685 | "call is ambiguous {group.name}({arguments |> join(", ")}), tried {get_sorted_function_list_as_string(ambiguous_matches!)}" | |
| 686 | ) | |
| 687 | elif tried.count > 0 then | |
| 688 | // When an actual still carries another function's | |
| 689 | // method-level type parameter, the callee was found | |
| 690 | // but a type argument could not be settled — prefer | |
| 691 | // the inference diagnostic over "no overload found". | |
| 692 | let caller = IoC.CONTAINER.instance.symbol_table.current_function | |
| 693 | ||
| 694 | if arguments |> any(a => a.has_function_generic_argument_foreign_to(caller)) then | |
| 695 | _logger.error(location, "cannot infer type here") | |
| 696 | else | |
| 697 | _logger.error( | |
| 698 | location, | |
| 699 | "no {maybe_static}overload found for {group.name}({arguments |> join(", ")}), tried {get_sorted_function_list_as_string(tried)}" | |
| 700 | ) | |
| 701 | fi | |
| 702 | else | |
| 703 | _logger.error(location, "no {maybe_static}overload found for {group.name}({arguments |> join(", ")})") | |
| 704 | fi | |
| 705 | ||
| 706 | return null | |
| 707 | si | |
| 708 | ||
| 709 | _declares_argument_pack(function: Symbols.Function) -> bool is | |
| 710 | for argument in function.generic_arguments do | |
| 711 | if argument.symbol.is_argument_pack then | |
| 712 | return true | |
| 713 | fi | |
| 714 | od | |
| 715 | ||
| 716 | return false | |
| 717 | si | |
| 718 | ||
| 719 | get_sorted_function_list_as_string(functions: Collections.Iterable[Symbols.Function]) -> string static => | |
| 720 | functions |> | |
| 721 | map(f => f.to_string()) |> | |
| 722 | sort() |> | |
| 723 | join() | |
| 724 | ||
| 725 | // For each (formal, actual) pair on the chosen overload, push | |
| 726 | // type-arg constraints into any INFERRED_VARIABLE_TYPE | |
| 727 | // placeholders found on either side. The accumulator is | |
| 728 | // retrieved on the next iteration's lambda arg-compile / con- | |
| 729 | // structor re-walk to resolve the placeholder to a concrete | |
| 730 | // type. When add_constraint returns true (a real new constraint | |
| 731 | // landed), signal progress to the retry loop via | |
| 732 | // mark_consumed_any. | |
| 733 | _propagate_chosen_match_args( | |
| 734 | chosen: Symbols.Function, | |
| 735 | actual_types: Collections.List[Type] | |
| 736 | ) is | |
| 737 | // `x =~ y` resolves over `T?` exactly when it resolves over | |
| 738 | // `T`, so its formals say nothing about whether an operand | |
| 739 | // is optional, and a placeholder operand learns no bound | |
| 740 | // from them. | |
| 741 | if chosen.name =~ "=~" then | |
| 742 | return | |
| 743 | fi | |
| 744 | ||
| 745 | let unspecialized = chosen.unspecialized_arguments ?? chosen.arguments | |
| 746 | let caller = IoC.CONTAINER.instance.symbol_table.current_function | |
| 747 | let count = if chosen.arguments.count < actual_types.count then chosen.arguments.count else actual_types.count fi | |
| 748 | ||
| 749 | for i in 0..count do | |
| 750 | if i < unspecialized.count /\ _callee_parameter_slot.binds_placeholder(unspecialized[i], actual_types[i], caller) then | |
| 751 | continue | |
| 752 | fi | |
| 753 | ||
| 754 | match_propagator.propagate_match(chosen.arguments[i], actual_types[i]) | |
| 755 | od | |
| 756 | si | |
| 757 | ||
| 758 | _find_matches( | |
| 759 | group: Symbols.FUNCTION_GROUP, | |
| 760 | arguments: Collections.List[Type] | |
| 761 | ) -> OVERLOAD_MATCHES_RESULT? | |
| 762 | is | |
| 763 | if group.functions.count == 0 then | |
| 764 | return null | |
| 765 | fi | |
| 766 | ||
| 767 | if group.functions.count == 1 \/ arguments.count == 0 then | |
| 768 | return OVERLOAD_MATCHES_RESULT(group.functions, 0, -1) | |
| 769 | fi | |
| 770 | ||
| 771 | let results = Collections.LIST[Symbols.Function]() | |
| 772 | ||
| 773 | let best_score mut = cast int(Types.MATCH.DIFFERENT) * arguments.count | |
| 774 | let best_index mut = -1 | |
| 775 | ||
| 776 | for f in group.functions do | |
| 777 | if f.arguments.count >= arguments.count then | |
| 778 | let score mut = cast int(Types.MATCH.SAME) | |
| 779 | ||
| 780 | for i in 0..arguments.count do | |
| 781 | let match: Types.MATCH mut | |
| 782 | ||
| 783 | match = f.arguments[i].compare(arguments[i]) | |
| 784 | ||
| 785 | if match == Types.MATCH.DIFFERENT then | |
| 786 | score = cast int(Types.MATCH.DIFFERENT) | |
| 787 | fi | |
| 788 | ||
| 789 | score = score + cast int(match) | |
| 790 | od | |
| 791 | ||
| 792 | results.add(f) | |
| 793 | ||
| 794 | if score < best_score then | |
| 795 | best_score = score | |
| 796 | best_index = results.count - 1 | |
| 797 | fi | |
| 798 | fi | |
| 799 | od | |
| 800 | ||
| 801 | return | |
| 802 | OVERLOAD_MATCHES_RESULT( | |
| 803 | results, | |
| 804 | best_index, | |
| 805 | -1 | |
| 806 | ) | |
| 807 | si | |
| 808 | si | |
| 809 | si |