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Check for invalid cycles after type solving recursive defs

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Disallow cycles that pass through a non-function value. Since we
evaluate eagerly, having one such cycle means there is at least one path
in the program that (likely) has unbounded recursion. Of course we can't
be certain (halting problem), but it's very likely, and avoids stuff
like #1926. Also, mono (as it's done today) won't work if things in a
cycle aren't functions.

Closes #1926
This commit is contained in:
Ayaz Hafiz 2022-05-10 16:02:10 -04:00
parent 17d8545510
commit 710a10a29c
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GPG key ID: 0E2A37416A25EF58
17 changed files with 261 additions and 49 deletions
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10
compiler/can/src/expr.rs
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@ -19,7 +19,7 @@ use roc_parse::ast::{self, EscapedChar, StrLiteral};
use roc_parse::pattern::PatternType::*;
use roc_problem::can::{PrecedenceProblem, Problem, RuntimeError};
use roc_region::all::{Loc, Region};
use roc_types::subs::{ExhaustiveMark, RedundantMark, VarStore, Variable};
use roc_types::subs::{ExhaustiveMark, IllegalCycleMark, RedundantMark, VarStore, Variable};
use roc_types::types::{Alias, Category, LambdaSet, OptAbleVar, Type};
use std::fmt::{Debug, Display};
use std::{char, u32};
@ -115,7 +115,7 @@ pub enum Expr {
},
// Let
LetRec(Vec<Def>, Box<Loc<Expr>>),
LetRec(Vec<Def>, Box<Loc<Expr>>, IllegalCycleMark),
LetNonRec(Box<Def>, Box<Loc<Expr>>),
/// This is *only* for calling functions, not for tag application.
@ -224,7 +224,7 @@ impl Expr {
&Self::AbilityMember(sym, _, _) => Category::Lookup(sym),
Self::When { .. } => Category::When,
Self::If { .. } => Category::If,
Self::LetRec(_, expr) => expr.value.category(),
Self::LetRec(_, expr, _) => expr.value.category(),
Self::LetNonRec(_, expr) => expr.value.category(),
&Self::Call(_, _, called_via) => Category::CallResult(None, called_via),
&Self::RunLowLevel { op, .. } => Category::LowLevelOpResult(op),
@ -1516,7 +1516,7 @@ pub fn inline_calls(var_store: &mut VarStore, scope: &mut Scope, expr: Expr) ->
Expect(Box::new(loc_condition), Box::new(loc_expr))
}
LetRec(defs, loc_expr) => {
LetRec(defs, loc_expr, mark) => {
let mut new_defs = Vec::with_capacity(defs.len());
for def in defs {
@ -1537,7 +1537,7 @@ pub fn inline_calls(var_store: &mut VarStore, scope: &mut Scope, expr: Expr) ->
value: inline_calls(var_store, scope, loc_expr.value),
};
LetRec(new_defs, Box::new(loc_expr))
LetRec(new_defs, Box::new(loc_expr), mark)
}
LetNonRec(def, loc_expr) => {