Deep copy type variables

compiler/mono/src/copy.rs

@@ -0,0 +1,298 @@
+use bumpalo::collections::Vec;
+use bumpalo::Bump;
+use roc_types::subs::{
+    AliasVariables, Descriptor, OptVariable, RecordFields, Subs, SubsSlice, UnionTags, Variable,
+    VariableSubsSlice,
+};
+
+pub fn deep_copy_type_vars<'a>(
+    arena: &'a Bump,
+    subs: &mut Subs,
+    var: Variable,
+) -> Vec<'a, (Variable, Variable)> {
+    let mut copied = Vec::with_capacity_in(16, arena);
+
+    let cloned_var = help(arena, subs, &mut copied, var);
+
+    debug_assert!(match cloned_var {
+        Some(_) => copied.is_empty(),
+        None => !copied.is_empty(),
+    });
+
+    // we have tracked all visited variables, and can now traverse them
+    // in one go (without looking at the UnificationTable) and clear the copy field
+    let mut result = Vec::with_capacity_in(copied.len(), arena);
+    for var in copied {
+        let descriptor = subs.get_ref_mut(var);
+
+        if let Some(copy) = descriptor.copy.into_variable() {
+            result.push((var, copy));
+            descriptor.copy = OptVariable::NONE;
+        } else {
+            debug_assert!(false, "{:?} marked as copied but it wasn't", var);
+        }
+    }
+
+    return result;
+
+    #[must_use]
+    fn help(
+        arena: &Bump,
+        subs: &mut Subs,
+        visited: &mut Vec<Variable>,
+        var: Variable,
+    ) -> Option<Variable> {
+        use roc_types::subs::Content::*;
+        use roc_types::subs::FlatType::*;
+
+        let desc = subs.get_ref_mut(var);
+        let content = desc.content;
+        let rank = desc.rank;
+        let mark = desc.mark;
+
+        // Unlike `deep_copy_var` in solve, here we are cloning *all* flex and rigid vars.
+        // So we only want to fast-return if we've already done the cloning work for a particular
+        // var.
+        if let Some(copy) = desc.copy.into_variable() {
+            return Some(copy);
+        }
+
+        macro_rules! descend_slice {
+            ($slice:expr, $needs_clone:ident) => {
+                for var_index in $slice {
+                    let var = subs[var_index];
+                    $needs_clone = $needs_clone || help(arena, subs, visited, var).is_some();
+                }
+            };
+        }
+
+        macro_rules! descend_var {
+            ($var:expr, $needs_clone:ident) => {{
+                let new_var = help(arena, subs, visited, $var).unwrap_or($var);
+                $needs_clone = $needs_clone || new_var != $var;
+                new_var
+            }};
+        }
+
+        macro_rules! clone_var_slice {
+            ($slice:expr) => {{
+                let new_arguments = VariableSubsSlice::reserve_into_subs(subs, $slice.len());
+                for (target_index, var_index) in (new_arguments.indices()).zip($slice) {
+                    let var = subs[var_index];
+                    let copy_var = subs.get_ref(var).copy.into_variable().unwrap_or(var);
+                    subs.variables[target_index] = copy_var;
+                }
+                new_arguments
+            }};
+        }
+
+        // Now we recursively copy the content of the variable.
+        // We have already marked the variable as copied, so we
+        // will not repeat this work or crawl this variable again.
+        let opt_new_content = match content {
+            // The vars for which we want to do something interesting.
+            FlexVar(opt_name) => Some(FlexVar(opt_name)),
+            FlexAbleVar(opt_name, ability) => Some(FlexAbleVar(opt_name, ability)),
+            RigidVar(name) => Some(RigidVar(name)),
+            RigidAbleVar(name, ability) => Some(RigidAbleVar(name, ability)),
+
+            // Everything else is a mechanical descent.
+            Structure(flat_type) => match flat_type {
+                EmptyRecord | EmptyTagUnion | Erroneous(_) => None,
+                Apply(symbol, arguments) => {
+                    let mut needs_clone = false;
+                    descend_slice!(arguments, needs_clone);
+
+                    if needs_clone {
+                        let new_arguments = clone_var_slice!(arguments);
+                        Some(Structure(Apply(symbol, new_arguments)))
+                    } else {
+                        None
+                    }
+                }
+                Func(arguments, closure_var, ret_var) => {
+                    let mut needs_clone = false;
+
+                    descend_slice!(arguments, needs_clone);
+
+                    let new_closure_var = descend_var!(closure_var, needs_clone);
+                    let new_ret_var = descend_var!(ret_var, needs_clone);
+
+                    if needs_clone {
+                        let new_arguments = clone_var_slice!(arguments);
+                        Some(Structure(Func(new_arguments, new_closure_var, new_ret_var)))
+                    } else {
+                        None
+                    }
+                }
+                Record(fields, ext_var) => {
+                    let mut needs_clone = false;
+
+                    let new_ext_var = descend_var!(ext_var, needs_clone);
+
+                    descend_slice!(fields.variables(), needs_clone);
+
+                    if needs_clone {
+                        let new_variables = clone_var_slice!(fields.variables());
+                        let new_fields = {
+                            RecordFields {
+                                length: fields.length,
+                                field_names_start: fields.field_names_start,
+                                variables_start: new_variables.start,
+                                field_types_start: fields.field_types_start,
+                            }
+                        };
+                        Some(Structure(Record(new_fields, new_ext_var)))
+                    } else {
+                        None
+                    }
+                }
+                TagUnion(tags, ext_var) => {
+                    let mut needs_clone = false;
+
+                    let new_ext_var = descend_var!(ext_var, needs_clone);
+
+                    for variables_slice_index in tags.variables() {
+                        let variables_slice = subs[variables_slice_index];
+                        descend_slice!(variables_slice, needs_clone);
+                    }
+
+                    if needs_clone {
+                        let new_variable_slices =
+                            SubsSlice::reserve_variable_slices(subs, tags.len());
+                        let it = (new_variable_slices.indices()).zip(tags.variables());
+                        for (target_index, index) in it {
+                            let slice = subs[index];
+                            let new_variables = clone_var_slice!(slice);
+                            subs.variable_slices[target_index] = new_variables;
+                        }
+
+                        let new_union_tags =
+                            UnionTags::from_slices(tags.tag_names(), new_variable_slices);
+
+                        Some(Structure(TagUnion(new_union_tags, new_ext_var)))
+                    } else {
+                        None
+                    }
+                }
+                RecursiveTagUnion(rec_var, tags, ext_var) => {
+                    let mut needs_clone = false;
+
+                    let new_ext_var = descend_var!(ext_var, needs_clone);
+                    let new_rec_var = descend_var!(rec_var, needs_clone);
+
+                    for variables_slice_index in tags.variables() {
+                        let variables_slice = subs[variables_slice_index];
+                        descend_slice!(variables_slice, needs_clone);
+                    }
+
+                    if needs_clone {
+                        let new_variable_slices =
+                            SubsSlice::reserve_variable_slices(subs, tags.len());
+                        let it = (new_variable_slices.indices()).zip(tags.variables());
+                        for (target_index, index) in it {
+                            let slice = subs[index];
+                            let new_variables = clone_var_slice!(slice);
+                            subs.variable_slices[target_index] = new_variables;
+                        }
+
+                        let new_union_tags =
+                            UnionTags::from_slices(tags.tag_names(), new_variable_slices);
+
+                        Some(Structure(RecursiveTagUnion(
+                            new_rec_var,
+                            new_union_tags,
+                            new_ext_var,
+                        )))
+                    } else {
+                        None
+                    }
+                }
+                FunctionOrTagUnion(tag_name, symbol, ext_var) => {
+                    let mut needs_clone = false;
+                    let new_ext_var = descend_var!(ext_var, needs_clone);
+                    if needs_clone {
+                        Some(Structure(FunctionOrTagUnion(tag_name, symbol, new_ext_var)))
+                    } else {
+                        None
+                    }
+                }
+            },
+
+            RecursionVar {
+                opt_name,
+                structure,
+            } => {
+                let mut needs_clone = false;
+
+                let new_structure = descend_var!(structure, needs_clone);
+
+                if needs_clone {
+                    Some(RecursionVar {
+                        opt_name,
+                        structure: new_structure,
+                    })
+                } else {
+                    None
+                }
+            }
+
+            Alias(symbol, arguments, real_type_var, kind) => {
+                let mut needs_clone = false;
+
+                let new_real_type_var = descend_var!(real_type_var, needs_clone);
+                descend_slice!(arguments.all_variables(), needs_clone);
+
+                if needs_clone {
+                    let new_variables = clone_var_slice!(arguments.all_variables());
+                    let new_arguments = AliasVariables {
+                        variables_start: new_variables.start,
+                        ..arguments
+                    };
+
+                    Some(Alias(symbol, new_arguments, new_real_type_var, kind))
+                } else {
+                    None
+                }
+            }
+
+            RangedNumber(typ, range_vars) => {
+                let mut needs_clone = false;
+
+                let new_typ = descend_var!(typ, needs_clone);
+                descend_slice!(range_vars, needs_clone);
+
+                if needs_clone {
+                    let new_range_vars = clone_var_slice!(range_vars);
+
+                    Some(RangedNumber(new_typ, new_range_vars))
+                } else {
+                    None
+                }
+            }
+            Error => None,
+        };
+
+        if let Some(new_content) = opt_new_content {
+            visited.push(var);
+
+            let copy_descriptor = Descriptor {
+                content: new_content,
+                rank,
+                mark,
+                copy: OptVariable::NONE,
+            };
+
+            let copy = subs.fresh(copy_descriptor);
+            // Set the copy on the original var
+            subs.get_ref_mut(var).copy = copy.into();
+
+            // We had to create a fresh var for this type, so anything that depends on it should be
+            // freshened too, and use this fresh var.
+            return Some(copy);
+        }
+
+        // Doesn't need to be freshened; use the old var.
+        None
+    }
+}