1	# graph/fan_in: warn when more than `max` different defs of the program use one def (default 20).
2	#
3	# Fan-in is a def's weight: every caller depends on its contract, so a change to it spreads.
4	# Counted: the different defs, in the linted file and the files it imports, that reference the def
5	# (in their bodies or types). Not counted: itself, laws and their proofs (specs, not callers), Base,
6	# hub packages. By default only the linted file's own defs are reported (`imports` reports every
7	# local file of the program). Lint the entry file so that callers in imported files are seen.
8	# Options: max (default 20), imports (default false).
9	import Base
10	import ../vendor/lint.bend as Lint
11	import ../common.bend as Common
12	
13	def id() -> String:
14	  "graph/fan_in"
15	
16	def facts() -> Lint.Want:
17	  Lint.Want{Lint.Program{}, [], [], []}
18	
19	def message(+name: String, d: U32, max: U32) -> String:
20	  "def " ++ name ++ " is used by " ++ U32.show(d) ++ " different defs; the limit is " ++ U32.show(max) ++ ". Keep its contract small and stable, or split it by purpose."
21	
22	def judge.one(+d: U32, +max: U32, +owner: String, span: Maybe<&2, Lint.Span>) -> List<&2, Lint.Diag>:
23	  Common.when(
24	    U32.is_gt(d, max),
25	    Common.diag(Lint.Warning{}, message(owner, d, max), span)
26	  )
27	
28	def judge(
29	  seen: List<&2, Common.Seen>,
30	  +max: U32,
31	  +nodes: Set(),
32	  +into: Map<&2, List<&2, String>>,
33	  out: List<&2, Lint.Diag>
34	) -> List<&2, Lint.Diag>:
35	  match seen:
36	    case Nil{}:
37	      List.reverse(&2, Lint.Diag, out)
38	    case Con{Common.Seen{+owner, span}, rest}:
39	      judge(
40	        rest,
41	        max,
42	        nodes,
43	        into,
44	        Common.onto(
45	          judge.one(Common.degree(into, nodes, owner), max, owner, span),
46	          out
47	        )
48	      )
49	
50	def verdict(p: Common.Prog, max: U32, scope: Common.Scope) -> List<&2, Lint.Diag>:
51	  match p:
52	    case Common.Prog{seen, edges, into, nodes, laws}:
53	      judge(Common.scoped(scope, seen), max, nodes, into, [])
54	
55	def run(input: Lint.Input) -> IO(List<&2, Lint.Diag>):
56	  match input:
57	    case Lint.Input{+sources, +options}:
58	      do IO<List<&2, Lint.Diag>>:
59	        g : Common.Graph <- Lint.fold_facts(~Common.Graph, ~Common.Graph.collect, Common.Graph.empty())
60	        p : Common.Prog <- Common.Prog.of(sources, g)
61	        return verdict(p, Lint.option_number(options, "max", 20), Common.Scope.of(sources, options))
62	
63	def main() -> IO(Unit):
64	  Lint.serve(run)