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Treat rigids as flex vars when checking number range types

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ayazhafiz 2022-02-06 13:42:28 -05:00
parent 6d72971d6b
commit 680bf8e0b7
6 changed files with 75 additions and 55 deletions
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78
compiler/unify/src/unify.rs
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@ -1,3 +1,4 @@
use bitflags::bitflags;
use roc_module::ident::{Lowercase, TagName};
use roc_module::symbol::Symbol;
use roc_types::subs::Content::{self, *};
@ -56,17 +57,37 @@ macro_rules! mismatch {
type Pool = Vec<Variable>;
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum Mode {
/// Instructs the unifier to solve two types for equality.
///
/// For example, { n : Str }a ~ { n: Str, m : Str } will solve "a" to "{ m : Str }".
Eq,
/// Instructs the unifier to treat the right-hand-side of a constraint as
/// present in the left-hand-side, rather than strictly equal.
///
/// For example, t1 += [A Str] says we should "add" the tag "A Str" to the type of "t1".
Present,
bitflags! {
pub struct Mode : u8 {
/// Instructs the unifier to solve two types for equality.
///
/// For example, { n : Str }a ~ { n: Str, m : Str } will solve "a" to "{ m : Str }".
const EQ = 1 << 0;
/// Instructs the unifier to treat the right-hand-side of a constraint as
/// present in the left-hand-side, rather than strictly equal.
///
/// For example, t1 += [A Str] says we should "add" the tag "A Str" to the type of "t1".
const PRESENT = 1 << 1;
/// Instructs the unifier to treat rigids exactly like flex vars.
/// Usually rigids can only unify with flex vars, because rigids are named and bound
/// explicitly.
/// However, when checking type ranges, as we do for `RangedNumber` types, we must loosen
/// this restriction because otherwise an admissable range will appear inadmissable.
/// For example, Int * is in the range <I8, U8, ...>.
const RIGID_AS_FLEX = 1 << 2;
}
}
impl Mode {
fn is_eq(&self) -> bool {
debug_assert!(!self.contains(Mode::EQ | Mode::PRESENT));
self.contains(Mode::EQ)
}
fn is_present(&self) -> bool {
debug_assert!(!self.contains(Mode::EQ | Mode::PRESENT));
self.contains(Mode::PRESENT)
}
}
#[derive(Debug)]
@ -245,7 +266,7 @@ fn check_valid_range(
while let Some(&possible_var) = it.next() {
let snapshot = subs.snapshot();
let old_pool = pool.clone();
let outcome = unify_pool(subs, pool, var, possible_var, mode);
let outcome = unify_pool(subs, pool, var, possible_var, mode | Mode::RIGID_AS_FLEX);
if outcome.is_empty() {
// Okay, we matched some type in the range.
subs.rollback_to(snapshot);
@ -334,14 +355,14 @@ fn unify_structure(
// And if we see a flex variable on the right hand side of a presence
// constraint, we know we need to open up the structure we're trying to unify with.
match (ctx.mode, flat_type) {
(Mode::Present, FlatType::TagUnion(tags, _ext)) => {
match (ctx.mode.is_present(), flat_type) {
(true, FlatType::TagUnion(tags, _ext)) => {
let new_ext = subs.fresh_unnamed_flex_var();
let mut new_desc = ctx.first_desc.clone();
new_desc.content = Structure(FlatType::TagUnion(*tags, new_ext));
subs.set(ctx.first, new_desc);
}
(Mode::Present, FlatType::FunctionOrTagUnion(tn, sym, _ext)) => {
(true, FlatType::FunctionOrTagUnion(tn, sym, _ext)) => {
let new_ext = subs.fresh_unnamed_flex_var();
let mut new_desc = ctx.first_desc.clone();
new_desc.content = Structure(FlatType::FunctionOrTagUnion(*tn, *sym, new_ext));
@ -384,7 +405,7 @@ fn unify_structure(
Alias(_, _, real_var) => {
// NB: not treating this as a presence constraint seems pivotal! I
// can't quite figure out why, but it doesn't seem to impact other types.
unify_pool(subs, pool, ctx.first, *real_var, Mode::Eq)
unify_pool(subs, pool, ctx.first, *real_var, Mode::EQ)
}
RangedNumber(real_var, _) => unify_pool(subs, pool, ctx.first, *real_var, ctx.mode),
Error => merge(subs, ctx, Error),
@ -759,8 +780,8 @@ fn unify_tag_union_new(
let shared_tags = separate.in_both;
if let (Mode::Present, Content::Structure(FlatType::EmptyTagUnion)) =
(ctx.mode, subs.get(ext1).content)
if let (true, Content::Structure(FlatType::EmptyTagUnion)) =
(ctx.mode.is_present(), subs.get(ext1).content)
{
if !separate.only_in_2.is_empty() {
// Create a new extension variable that we'll fill in with the
@ -789,7 +810,7 @@ fn unify_tag_union_new(
if separate.only_in_1.is_empty() {
if separate.only_in_2.is_empty() {
let ext_problems = if ctx.mode == Mode::Eq {
let ext_problems = if ctx.mode.is_eq() {
unify_pool(subs, pool, ext1, ext2, ctx.mode)
} else {
// In a presence context, we don't care about ext2 being equal to ext1
@ -843,7 +864,7 @@ fn unify_tag_union_new(
let sub_record = fresh(subs, pool, ctx, Structure(flat_type));
// In a presence context, we don't care about ext2 being equal to tags1
if ctx.mode == Mode::Eq {
if ctx.mode.is_eq() {
let ext_problems = unify_pool(subs, pool, sub_record, ext2, ctx.mode);
if !ext_problems.is_empty() {
@ -866,7 +887,7 @@ fn unify_tag_union_new(
let unique_tags1 = UnionTags::insert_slices_into_subs(subs, separate.only_in_1);
let unique_tags2 = UnionTags::insert_slices_into_subs(subs, separate.only_in_2);
let ext_content = if ctx.mode == Mode::Present {
let ext_content = if ctx.mode.is_present() {
Content::Structure(FlatType::EmptyTagUnion)
} else {
Content::FlexVar(None)
@ -900,7 +921,7 @@ fn unify_tag_union_new(
return ext1_problems;
}
if ctx.mode == Mode::Eq {
if ctx.mode.is_eq() {
let ext2_problems = unify_pool(subs, pool, sub1, ext2, ctx.mode);
if !ext2_problems.is_empty() {
subs.rollback_to(snapshot);
@ -1295,7 +1316,7 @@ fn unify_zip_slices(
let l_var = subs[l_index];
let r_var = subs[r_index];
problems.extend(unify_pool(subs, pool, l_var, r_var, Mode::Eq));
problems.extend(unify_pool(subs, pool, l_var, r_var, Mode::EQ));
}
problems
@ -1309,9 +1330,14 @@ fn unify_rigid(subs: &mut Subs, ctx: &Context, name: &Lowercase, other: &Content
merge(subs, ctx, RigidVar(name.clone()))
}
RigidVar(_) | RecursionVar { .. } | Structure(_) | Alias(_, _, _) | RangedNumber(..) => {
// Type mismatch! Rigid can only unify with flex, even if the
// rigid names are the same.
mismatch!("Rigid {:?} with {:?}", ctx.first, &other)
if !ctx.mode.contains(Mode::RIGID_AS_FLEX) {
// Type mismatch! Rigid can only unify with flex, even if the
// rigid names are the same.
mismatch!("Rigid {:?} with {:?}", ctx.first, &other)
} else {
// We are treating rigid vars as flex vars; admit this
merge(subs, ctx, other.clone())
}
}
Error => {
// Error propagates.