src/semantic/symbols/ineffective_trait_override_checker.ghul

1		namespace Semantic.Symbols is
2		use Logging
3		use Source
4
5		use Types.Type
6
7		// Detects the .NET DIM trap where a class B overrides a trait default
8		// method whose owning trait T enters B's class chain at an intermediate
9		// class A that does not itself redeclare the member. In that case A has
10		// no vtable slot for the member, so B's "override" lands in a new slot
11		// and any dispatch routed through an A- or T-typed reference resolves
12		// to T's default rather than B's body.
13		//
14		// The fix is to redeclare the member in A (typically as
15		// `name: T => super.name;`), which forces a vtable slot the override
16		// can latch onto.
17		class INEFFECTIVE_TRAIT_OVERRIDE_CHECKER is
18		init() is si
19
20		check(
21		into: Classy?,
22		overrider_location: LOCATION,
23		overrider_description: string,
24		overridee: Symbol,
25		member_name: string,
26		trait_owner: Classy?,
27		logger: Logger
28		)
29		is
30		if !into? \/ !trait_owner? \/ !trait_owner.is_trait then
31		return
32		fi
33
34		if !into.is_class \/ into.is_reflected then
35		return
36		fi
37
38		let intermediate = _find_intermediate_without_redeclaration(into, trait_owner, member_name)
39
40		if intermediate? then
41		logger.error(
42		overrider_location,
43		"{overrider_description} does not override {overridee} because {intermediate.qualified_name} does not redeclare it",
44		intermediate.location,
45		"help: redeclare {member_name} here to allow overriding"
46		)
47		fi
48		si
49
50		_find_intermediate_without_redeclaration(start: Classy, trait_owner: Classy, member_name: string) -> Classy? is
51		let current: Classy? mut = _direct_class_parent(start)
52
53		while current? do
54		if _has_trait_in_direct_ancestors(current, trait_owner) then
55		if !_class_declares_member(current, member_name) then
56		return current
57		fi
58		return null
59		fi
60
61		current = _direct_class_parent(current)
62		od
63
64		return null
65		si
66
67		_direct_class_parent(classy: Classy) -> Classy? is
68		for a in classy.ancestors do
69		if !a.is_trait /\ isa Classy(a.symbol) then
70		return cast Classy?(a.symbol)!
71		fi
72		od
73
74		return null
75		si
76
77		_has_trait_in_direct_ancestors(classy: Classy, trait_owner: Classy) -> bool is
78		let trait_unspec = trait_owner.unspecialized_symbol
79
80		for a in classy.ancestors do
81		if a.is_trait /\ a.unspecialized_symbol == trait_unspec then
82		return true
83		fi
84		od
85
86		return false
87		si
88
89		_class_declares_member(classy: Classy, name: string) -> bool is
90		let direct = classy.find_direct(name)
91
92		if !direct? then
93		return false
94		fi
95
96		let classy_unspec = classy.unspecialized_symbol
97
98		if isa FUNCTION_GROUP(direct) then
99		for f in direct.functions do
100		if f.is_default_trait_method \/ f.is_abstract then
101		continue
102		fi
103
104		if f.owner? /\ f.owner.unspecialized_symbol == classy_unspec then
105		return true
106		fi
107		od
108
109		return false
110		fi
111
112		if isa Property(direct) then
113		let prop = direct
114		let read_is_default = prop.read_function? /\ prop.read_function.is_default_trait_method
115		let assign_is_default = prop.assign_function? /\ prop.assign_function.is_default_trait_method
116
117		if read_is_default /\ (!prop.assign_function? \/ assign_is_default) then
118		return false
119		fi
120		fi
121
122		return direct.owner? /\ direct.owner.unspecialized_symbol == classy_unspec
123		si
124		si
125		si