src/rules/correctness/twice.bend source

src/rules/correctness/twice.bend on the hub · documented module

# rule twice: a list pattern in a def that calls itself, opening with the# same literal twice (`case 10 <> 10 <> _:`, `case Con{'a', Con{'a', t}}:`).# The checker hangs on it (pi-bend BEND-018, b6a83a52; bend 2.0.16 still# does). Only the opening pair was seen to hang: `10 <> 11 <> 10`,# `_ <> 10 <> 10` and `10 <> 11 <> 11` check at once, and so does the same# pattern in a def that does not recurse. Match one element per step, with a# state. A def recurses when its body calls it, `name(..)`: a parameter or a# value named like the def is not a call. Only a case's first match column is# read: a list pattern in a later column of `match a b:` is not.import Baseimport ../../src.bend as Srcimport ../../finding.bend as Fimport ../../syntax/lex.bend as Leximport ../../syntax/tree.bend as Treeimport ../../syntax/bind.bend as Bindimport ../../lazy/lazy.bend as Lazyimport ../tokens.bend as Timport ../calls.bend as Calls# the literal a list pattern opens with: `x <> ..` or `Con{x, ..}`def head(pat: Tree.Node) -> Maybe<&2, Lex.Tok>:  match pat:    case Tree.NCons{Tree.Leaf{Lex.Tok{+k, +t, l, c}}, Tree.NCons{Tree.Leaf{Lex.Tok{k2, +o, l2, c2}}, rest}}:      Bool.pick(Maybe<&2, Lex.Tok>, Bool.and(T.is_lit(k), String.eq(o, "<>")), Some{Lex.Tok{k, t, l, c}}, None{})    case Tree.NCons{Tree.Leaf{Lex.Tok{Lex.TUpper{}, +t, l, c}},        Tree.NCons{Tree.Group{open, Tree.NCons{Tree.Leaf{Lex.Tok{+k, +x, l2, c2}}, kids}, close}, rest}}:      Bool.pick(Maybe<&2, Lex.Tok>, Bool.and(String.eq(t, "Con"), T.is_lit(k)), Some{Lex.Tok{k, x, l2, c2}}, None{})    case other:      None{}# the rest of a list pattern after its first elementdef tail(pat: Tree.Node) -> Tree.Node:  match pat:    case Tree.NCons{Tree.Leaf{Lex.Tok{Lex.TUpper{}, t, l, c}},        Tree.NCons{Tree.Group{open, Tree.NCons{x, Tree.NCons{comma, kids}}, close}, rest}}:      kids    case Tree.NCons{x, Tree.NCons{op, rest}}:      rest    case other:      Tree.NNil{}# a finding at the second literal when it repeats the firstdef same(aa: Maybe<&2, Lex.Tok>, bb: Maybe<&2, Lex.Tok>, +path: String) -> List<&2, F.Finding>:  match aa bb:    case Some{Lex.Tok{k, +t, l, c}} Some{Lex.Tok{k2, +t2, l2, c2}}:      Bool.pick(List<&2, F.Finding>, String.eq(t, t2),        [F.Finding{path, l2, c2, T.width(t2), "twice",          "This literal appears twice in one list pattern, which makes the checker hang; match one element per step."}],        [])    case a2 b2:      []# a case statement's pattern, checkeddef arm(+pat: Tree.Node, +path: String) -> List<&2, F.Finding>:  same(head(pat), head(tail(pat)), path)# every case statement under a recursive def, at any depthdef walk(nn: Tree.Node, +path: String) -> List<&2, F.Finding>:  match nn:    case Tree.NCons{Tree.Stmt{Tree.SCase{}, kids, body}, rest}:      List.concat(&2, F.Finding, [arm(T.pattern(kids), path), walk(body, path), walk(rest, path)])    case Tree.NCons{Tree.Stmt{kind, kids, body}, rest}:      List.append(&2, F.Finding, walk(body, path), walk(rest, path))    case Tree.NCons{h, rest}:      walk(rest, path)    case other:      Nil{}# a def's body, when it calls itselfdef check.def(mm: Maybe<&2, String>, +body: Tree.Node, path: String) -> List<&2, F.Finding>:  match mm:    case None{}:      Nil{}    case Some{+name}:      Lazy.stop(List<&2, F.Finding>, Bool.not(Calls.calls(body, name)), [], _u => walk(body, path))def check.go(root: Tree.Node, +path: String) -> List<&2, F.Finding>:  match root:    case Tree.NCons{Tree.Stmt{Tree.SDef{}, +kids, body}, rest}:      List.append(&2, F.Finding, check.def(Bind.declared(kids), body, path), check.go(rest, path))    case Tree.NCons{h, rest}:      check.go(rest, path)    case other:      Nil{}# the ruledef check(ss: Src.Src) -> List<&2, F.Finding>:  Src.Src{path, text, toks, tree, bound, items} = ss  check.go(tree, path)