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| 1 | namespace Semantic is | |
| 2 | use Logging | |
| 3 | use Types.Type | |
| 4 | ||
| 5 | // Pushes constraints onto INFERRED_VARIABLE_TYPE placeholders by | |
| 6 | // walking paired (formal, actual) types and recording the | |
| 7 | // opposite side's concrete type as a constraint on the | |
| 8 | // placeholder's `origin`. When a placeholder learns a new | |
| 9 | // constraint, the underlying logger's `mark_consumed_any` is | |
| 10 | // called so the iterative body-retry loop knows to walk again. | |
| 11 | // | |
| 12 | // Three shapes are recognised: | |
| 13 | // | |
| 14 | // - actual is placeholder, formal concrete -> formal as | |
| 15 | // UPPER bound on actual.origin (the placeholder is being | |
| 16 | // passed AS the formal — formal places an upper-bound | |
| 17 | // "must be assignable to" constraint, never widens the | |
| 18 | // placeholder's lower-bound LUB). | |
| 19 | // | |
| 20 | // - formal is placeholder, actual concrete -> actual as | |
| 21 | // LOWER bound on formal.origin (lambda-arg match propagation: | |
| 22 | // drives #1210 inference where a concrete call-site | |
| 23 | // actual tells the lambda's parameter what value type it | |
| 24 | // must accept; constructor-type-arg match propagation similarly). | |
| 25 | // | |
| 26 | // - same generic head on both sides -> recurse on | |
| 27 | // paired type-args. Picks up call-arg-as-constraint cases | |
| 28 | // where actual is `Box[placeholder]` and formal is `Box[int]`. | |
| 29 | // | |
| 30 | // - outer heads differ but actual *extends* formal's head -> | |
| 31 | // walk actual's specialised ancestors looking for a match | |
| 32 | // and recurse on that. Picks up union variants (`NIL[T]` -> | |
| 33 | // `List[int]`) and trait-implementation arguments. | |
| 34 | class MATCH_PROPAGATOR(_logger: Logger) is | |
| 35 | _delegate_shape: DELEGATE_SHAPE | |
| 36 | _enclosing_type_variable: ENCLOSING_TYPE_VARIABLE | |
| 37 | ||
| 38 | super() | |
| 39 | ||
| 40 | init(..) is | |
| 41 | _delegate_shape = DELEGATE_SHAPE() | |
| 42 | _enclosing_type_variable = ENCLOSING_TYPE_VARIABLE() | |
| 43 | si | |
| 44 | ||
| 45 | // Top-level entry. Safe to call with null on either side | |
| 46 | // (no-op). When a constraint is recorded, `mark_consumed_any` | |
| 47 | // is invoked on the logger so the retry loop continues. | |
| 48 | propagate_match(formal: Type?, actual: Type?) is | |
| 49 | if !formal? \/ !actual? then | |
| 50 | return | |
| 51 | fi | |
| 52 | ||
| 53 | // A named delegate slot constrains a function actual by its | |
| 54 | // call shape: the heads never match otherwise, so a literal | |
| 55 | // still inferring its parameter types would learn nothing | |
| 56 | // from the slot it is being passed to. | |
| 57 | if actual.is_function /\ _delegate_shape.is_named_delegate(formal, IoC.CONTAINER.instance.innate_symbol_lookup) then | |
| 58 | let shape = | |
| 59 | _delegate_shape.try_get_function_type( | |
| 60 | formal, | |
| 61 | IoC.CONTAINER.instance.innate_symbol_lookup) | |
| 62 | ||
| 63 | if shape? then | |
| 64 | propagate_match(shape, actual) | |
| 65 | fi | |
| 66 | ||
| 67 | return | |
| 68 | fi | |
| 69 | ||
| 70 | // A type variable of a declaration this code is written | |
| 71 | // inside already stands for a definite type here, so it | |
| 72 | // settles a slot as readily as a concrete type would. The | |
| 73 | // bound is a lower one, matching how a sibling | |
| 74 | // type-argument binding pushes one back, and it is taken | |
| 75 | // from whichever side carries the variable. A variable | |
| 76 | // belonging to the declaration being resolved is left | |
| 77 | // alone: it is itself what the resolution is working out. | |
| 78 | if | |
| 79 | isa Types.INFERRED_VARIABLE_TYPE(actual) /\ | |
| 80 | formal.is_type_variable /\ | |
| 81 | _enclosing_type_variable.is_fixed_in( | |
| 82 | formal, | |
| 83 | IoC.CONTAINER.instance.symbol_table.current_function) | |
| 84 | then | |
| 85 | let placeholder = actual | |
| 86 | _logger.mark_consumed_any_if(Semantic.INFERENCE_TRACE.add_lower_bound("match.formal_type_variable", placeholder.origin, formal)) | |
| 87 | return | |
| 88 | fi | |
| 89 | ||
| 90 | if | |
| 91 | isa Types.INFERRED_VARIABLE_TYPE(formal) /\ | |
| 92 | actual.is_type_variable /\ | |
| 93 | _enclosing_type_variable.is_fixed_in( | |
| 94 | actual, | |
| 95 | IoC.CONTAINER.instance.symbol_table.current_function) | |
| 96 | then | |
| 97 | let placeholder = formal | |
| 98 | _logger.mark_consumed_any_if(Semantic.INFERENCE_TRACE.add_lower_bound("match.actual_type_variable", placeholder.origin, actual)) | |
| 99 | return | |
| 100 | fi | |
| 101 | ||
| 102 | if | |
| 103 | isa Types.INFERRED_VARIABLE_TYPE(actual) /\ | |
| 104 | !formal.is_sentinel /\ !formal.is_type_variable | |
| 105 | then | |
| 106 | let placeholder = actual | |
| 107 | // Upper-bound, not lower: formal here is the slot the | |
| 108 | // placeholder must fit INTO. Treating it as a peer | |
| 109 | // LUB candidate widens spuriously when the slot is | |
| 110 | // a supertype of the placeholder's true value type | |
| 111 | // (eg. `g(v: object)` with `v = false` -> v widened | |
| 112 | // to object, breaking subsequent `if v`). | |
| 113 | _logger.mark_consumed_any_if(Semantic.INFERENCE_TRACE.add_upper_bound("match.placeholder_actual", placeholder.origin, formal)) | |
| 114 | return | |
| 115 | fi | |
| 116 | ||
| 117 | if | |
| 118 | isa Types.INFERRED_VARIABLE_TYPE(formal) /\ | |
| 119 | !actual.is_sentinel /\ !actual.is_type_variable | |
| 120 | then | |
| 121 | let placeholder = formal | |
| 122 | _logger.mark_consumed_any_if(Semantic.INFERENCE_TRACE.add_lower_bound("match.placeholder_formal", placeholder.origin, actual)) | |
| 123 | return | |
| 124 | fi | |
| 125 | ||
| 126 | // Recurse on structurally-matching generics (same outer | |
| 127 | // symbol, same arity): paired type-args may carry | |
| 128 | // placeholders even when the outer types compared cleanly. | |
| 129 | let formal_generic = cast Types.GENERIC?(formal) | |
| 130 | let actual_generic = cast Types.GENERIC?(actual) | |
| 131 | ||
| 132 | if formal_generic? /\ actual_generic? then | |
| 133 | let formal_symbol = cast Symbols.GENERIC?(formal_generic.symbol) | |
| 134 | let actual_symbol = cast Symbols.GENERIC?(actual_generic.symbol) | |
| 135 | ||
| 136 | if | |
| 137 | formal_symbol? /\ actual_symbol? /\ | |
| 138 | formal_symbol.symbol =~ actual_symbol.symbol /\ | |
| 139 | formal_generic.arguments.count == actual_generic.arguments.count | |
| 140 | then | |
| 141 | for j in 0..formal_generic.arguments.count do | |
| 142 | propagate_match(formal_generic.arguments[j], actual_generic.arguments[j]) | |
| 143 | od | |
| 144 | elif | |
| 145 | formal_symbol? /\ actual_symbol? /\ | |
| 146 | actual_symbol.ancestors.count > 0 | |
| 147 | then | |
| 148 | // Outer heads differ but actual may extend formal's | |
| 149 | // head — e.g. union variant NIL<placeholder> being | |
| 150 | // passed to a List<int> slot, or SACK<placeholder> | |
| 151 | // to a Sack<int> slot. Walk actual's specialised | |
| 152 | // ancestors looking for one whose head matches the | |
| 153 | // formal's. When found, recurse on the formal's | |
| 154 | // args paired against the specialised ancestor's, | |
| 155 | // which carries the placeholders in the right | |
| 156 | // positions for match propagation to take effect. | |
| 157 | for i in 0..actual_symbol.ancestors.count do | |
| 158 | let ancestor = actual_symbol.get_ancestor(i) | |
| 159 | ||
| 160 | if isa Types.GENERIC(ancestor) then | |
| 161 | let ancestor_generic = ancestor | |
| 162 | let ancestor_symbol = cast Symbols.GENERIC?(ancestor_generic.symbol) | |
| 163 | ||
| 164 | if | |
| 165 | ancestor_symbol? /\ | |
| 166 | ancestor_symbol.symbol =~ formal_symbol.symbol | |
| 167 | then | |
| 168 | propagate_match(formal, ancestor) | |
| 169 | return | |
| 170 | fi | |
| 171 | fi | |
| 172 | od | |
| 173 | fi | |
| 174 | fi | |
| 175 | si | |
| 176 | ||
| 177 | // Convenience overload for the common case of walking a | |
| 178 | // paired formal/actual list. Truncates to the shorter of the | |
| 179 | // two so a call site with mismatched argument counts (e.g. | |
| 180 | // a partial function-group resolution) still makes progress | |
| 181 | // on the prefix. | |
| 182 | propagate_matches( | |
| 183 | formals: Collections.List[Type]?, | |
| 184 | actuals: Collections.List[Type]? | |
| 185 | ) is | |
| 186 | if !formals? \/ !actuals? then | |
| 187 | return | |
| 188 | fi | |
| 189 | ||
| 190 | let count mut = formals.count | |
| 191 | ||
| 192 | if count > actuals.count then | |
| 193 | count = actuals.count | |
| 194 | fi | |
| 195 | ||
| 196 | for i in 0..count do | |
| 197 | propagate_match(formals[i], actuals[i]) | |
| 198 | od | |
| 199 | si | |
| 200 | si | |
| 201 | si |