Fast-path for determining ability member impls for builtin opaques

crates/compiler/derive_key/src/decoding.rs

@@ -78,24 +78,11 @@ impl FlatDecodable {
                 //
                 FlatType::Func(..) => Err(Underivable),
             },
-            Content::Alias(sym, _, real_var, _) => match sym {
+            Content::Alias(sym, _, real_var, _) => match from_builtin_symbol(sym) {
-                Symbol::BOOL_BOOL => Ok(Immediate(Symbol::DECODE_BOOL)),
+                Some(lambda) => Ok(lambda),
-                Symbol::NUM_U8 | Symbol::NUM_UNSIGNED8 => Ok(Immediate(Symbol::DECODE_U8)),
-                Symbol::NUM_U16 | Symbol::NUM_UNSIGNED16 => Ok(Immediate(Symbol::DECODE_U16)),
-                Symbol::NUM_U32 | Symbol::NUM_UNSIGNED32 => Ok(Immediate(Symbol::DECODE_U32)),
-                Symbol::NUM_U64 | Symbol::NUM_UNSIGNED64 => Ok(Immediate(Symbol::DECODE_U64)),
-                Symbol::NUM_U128 | Symbol::NUM_UNSIGNED128 => Ok(Immediate(Symbol::DECODE_U128)),
-                Symbol::NUM_I8 | Symbol::NUM_SIGNED8 => Ok(Immediate(Symbol::DECODE_I8)),
-                Symbol::NUM_I16 | Symbol::NUM_SIGNED16 => Ok(Immediate(Symbol::DECODE_I16)),
-                Symbol::NUM_I32 | Symbol::NUM_SIGNED32 => Ok(Immediate(Symbol::DECODE_I32)),
-                Symbol::NUM_I64 | Symbol::NUM_SIGNED64 => Ok(Immediate(Symbol::DECODE_I64)),
-                Symbol::NUM_I128 | Symbol::NUM_SIGNED128 => Ok(Immediate(Symbol::DECODE_I128)),
-                Symbol::NUM_DEC | Symbol::NUM_DECIMAL => Ok(Immediate(Symbol::DECODE_DEC)),
-                Symbol::NUM_F32 | Symbol::NUM_BINARY32 => Ok(Immediate(Symbol::DECODE_F32)),
-                Symbol::NUM_F64 | Symbol::NUM_BINARY64 => Ok(Immediate(Symbol::DECODE_F64)),
                 // NB: I believe it is okay to unwrap opaques here because derivers are only used
                 // by the backend, and the backend treats opaques like structural aliases.
-                _ => Self::from_var(subs, real_var),
+                None => Self::from_var(subs, real_var),
             },
             Content::RangedNumber(range) => {
                 Self::from_var(subs, range.default_compilation_variable())
@@ -110,4 +97,29 @@ impl FlatDecodable {
             Content::LambdaSet(_) => Err(Underivable),
         }
     }
+
+    pub(crate) fn from_builtin_symbol(symbol: Symbol) -> Result<FlatDecodable, DeriveError> {
+        from_builtin_symbol(symbol).ok_or(DeriveError::Underivable)
+    }
+}
+
+const fn from_builtin_symbol(symbol: Symbol) -> Option<FlatDecodable> {
+    use FlatDecodable::*;
+    match symbol {
+        Symbol::BOOL_BOOL => Some(Immediate(Symbol::DECODE_BOOL)),
+        Symbol::NUM_U8 | Symbol::NUM_UNSIGNED8 => Some(Immediate(Symbol::DECODE_U8)),
+        Symbol::NUM_U16 | Symbol::NUM_UNSIGNED16 => Some(Immediate(Symbol::DECODE_U16)),
+        Symbol::NUM_U32 | Symbol::NUM_UNSIGNED32 => Some(Immediate(Symbol::DECODE_U32)),
+        Symbol::NUM_U64 | Symbol::NUM_UNSIGNED64 => Some(Immediate(Symbol::DECODE_U64)),
+        Symbol::NUM_U128 | Symbol::NUM_UNSIGNED128 => Some(Immediate(Symbol::DECODE_U128)),
+        Symbol::NUM_I8 | Symbol::NUM_SIGNED8 => Some(Immediate(Symbol::DECODE_I8)),
+        Symbol::NUM_I16 | Symbol::NUM_SIGNED16 => Some(Immediate(Symbol::DECODE_I16)),
+        Symbol::NUM_I32 | Symbol::NUM_SIGNED32 => Some(Immediate(Symbol::DECODE_I32)),
+        Symbol::NUM_I64 | Symbol::NUM_SIGNED64 => Some(Immediate(Symbol::DECODE_I64)),
+        Symbol::NUM_I128 | Symbol::NUM_SIGNED128 => Some(Immediate(Symbol::DECODE_I128)),
+        Symbol::NUM_DEC | Symbol::NUM_DECIMAL => Some(Immediate(Symbol::DECODE_DEC)),
+        Symbol::NUM_F32 | Symbol::NUM_BINARY32 => Some(Immediate(Symbol::DECODE_F32)),
+        Symbol::NUM_F64 | Symbol::NUM_BINARY64 => Some(Immediate(Symbol::DECODE_F64)),
+        _ => None,
+    }
 }

crates/compiler/derive_key/src/encoding.rs

@@ -112,22 +112,8 @@ impl FlatEncodable {
                 //
                 FlatType::Func(..) => Err(Underivable),
             },
-            Content::Alias(sym, _, real_var, _) => match sym {
+            Content::Alias(sym, _, real_var, _) => match from_builtin_symbol(sym) {
-                Symbol::BOOL_BOOL => Ok(Immediate(Symbol::ENCODE_BOOL)),
+                Some(lambda) => Ok(lambda),
-                Symbol::NUM_U8 | Symbol::NUM_UNSIGNED8 => Ok(Immediate(Symbol::ENCODE_U8)),
-                Symbol::NUM_U16 | Symbol::NUM_UNSIGNED16 => Ok(Immediate(Symbol::ENCODE_U16)),
-                Symbol::NUM_U32 | Symbol::NUM_UNSIGNED32 => Ok(Immediate(Symbol::ENCODE_U32)),
-                Symbol::NUM_U64 | Symbol::NUM_UNSIGNED64 => Ok(Immediate(Symbol::ENCODE_U64)),
-                Symbol::NUM_U128 | Symbol::NUM_UNSIGNED128 => Ok(Immediate(Symbol::ENCODE_U128)),
-                Symbol::NUM_I8 | Symbol::NUM_SIGNED8 => Ok(Immediate(Symbol::ENCODE_I8)),
-                Symbol::NUM_I16 | Symbol::NUM_SIGNED16 => Ok(Immediate(Symbol::ENCODE_I16)),
-                Symbol::NUM_I32 | Symbol::NUM_SIGNED32 => Ok(Immediate(Symbol::ENCODE_I32)),
-                Symbol::NUM_I64 | Symbol::NUM_SIGNED64 => Ok(Immediate(Symbol::ENCODE_I64)),
-                Symbol::NUM_I128 | Symbol::NUM_SIGNED128 => Ok(Immediate(Symbol::ENCODE_I128)),
-                Symbol::NUM_DEC | Symbol::NUM_DECIMAL => Ok(Immediate(Symbol::ENCODE_DEC)),
-                Symbol::NUM_F32 | Symbol::NUM_BINARY32 => Ok(Immediate(Symbol::ENCODE_F32)),
-                Symbol::NUM_F64 | Symbol::NUM_BINARY64 => Ok(Immediate(Symbol::ENCODE_F64)),
-                Symbol::NUM_NAT | Symbol::NUM_NATURAL => Err(Underivable),
                 // TODO: I believe it is okay to unwrap opaques here because derivers are only used
                 // by the backend, and the backend treats opaques like structural aliases.
                 _ => Self::from_var(subs, real_var),
@@ -145,4 +131,30 @@ impl FlatEncodable {
             Content::LambdaSet(_) => Err(Underivable),
         }
     }
+
+    pub(crate) fn from_builtin_symbol(symbol: Symbol) -> Result<FlatEncodable, DeriveError> {
+        from_builtin_symbol(symbol).ok_or(DeriveError::Underivable)
+    }
+}
+
+const fn from_builtin_symbol(symbol: Symbol) -> Option<FlatEncodable> {
+    use FlatEncodable::*;
+    match symbol {
+        Symbol::BOOL_BOOL => Some(Immediate(Symbol::ENCODE_BOOL)),
+        Symbol::NUM_U8 | Symbol::NUM_UNSIGNED8 => Some(Immediate(Symbol::ENCODE_U8)),
+        Symbol::NUM_U16 | Symbol::NUM_UNSIGNED16 => Some(Immediate(Symbol::ENCODE_U16)),
+        Symbol::NUM_U32 | Symbol::NUM_UNSIGNED32 => Some(Immediate(Symbol::ENCODE_U32)),
+        Symbol::NUM_U64 | Symbol::NUM_UNSIGNED64 => Some(Immediate(Symbol::ENCODE_U64)),
+        Symbol::NUM_U128 | Symbol::NUM_UNSIGNED128 => Some(Immediate(Symbol::ENCODE_U128)),
+        Symbol::NUM_I8 | Symbol::NUM_SIGNED8 => Some(Immediate(Symbol::ENCODE_I8)),
+        Symbol::NUM_I16 | Symbol::NUM_SIGNED16 => Some(Immediate(Symbol::ENCODE_I16)),
+        Symbol::NUM_I32 | Symbol::NUM_SIGNED32 => Some(Immediate(Symbol::ENCODE_I32)),
+        Symbol::NUM_I64 | Symbol::NUM_SIGNED64 => Some(Immediate(Symbol::ENCODE_I64)),
+        Symbol::NUM_I128 | Symbol::NUM_SIGNED128 => Some(Immediate(Symbol::ENCODE_I128)),
+        Symbol::NUM_DEC | Symbol::NUM_DECIMAL => Some(Immediate(Symbol::ENCODE_DEC)),
+        Symbol::NUM_F32 | Symbol::NUM_BINARY32 => Some(Immediate(Symbol::ENCODE_F32)),
+        Symbol::NUM_F64 | Symbol::NUM_BINARY64 => Some(Immediate(Symbol::ENCODE_F64)),
+        Symbol::NUM_NAT | Symbol::NUM_NATURAL => None,
+        _ => None,
+    }
 }

crates/compiler/derive_key/src/hash.rs

@@ -143,6 +143,10 @@ impl FlatHash {
             Content::LambdaSet(_) => Err(Underivable),
         }
     }
+
+    pub fn from_builtin_symbol(symbol: Symbol) -> Result<FlatHash, DeriveError> {
+        builtin_symbol_to_hash_lambda(symbol).ok_or(DeriveError::Underivable)
+    }
 }
 
 const fn builtin_symbol_to_hash_lambda(symbol: Symbol) -> Option<FlatHash> {

crates/compiler/derive_key/src/lib.rs

@@ -52,7 +52,7 @@ impl DeriveKey {
     }
 }
 
-#[derive(Hash, PartialEq, Eq, Debug)]
+#[derive(Hash, Clone, PartialEq, Eq, Debug)]
 pub enum Derived {
     /// If a derived implementation name is well-known ahead-of-time, we can inline the symbol
     /// directly rather than associating a key for an implementation to be made later on.
@@ -123,4 +123,34 @@ impl Derived {
             }
         }
     }
+
+    pub fn builtin_with_builtin_symbol(
+        builtin: DeriveBuiltin,
+        symbol: Symbol,
+    ) -> Result<Self, DeriveError> {
+        match builtin {
+            DeriveBuiltin::ToEncoder => match encoding::FlatEncodable::from_builtin_symbol(symbol)?
+            {
+                FlatEncodable::Immediate(imm) => Ok(Derived::Immediate(imm)),
+                FlatEncodable::Key(repr) => Ok(Derived::Key(DeriveKey::ToEncoder(repr))),
+            },
+            DeriveBuiltin::Decoder => match decoding::FlatDecodable::from_builtin_symbol(symbol)? {
+                FlatDecodable::Immediate(imm) => Ok(Derived::Immediate(imm)),
+                FlatDecodable::Key(repr) => Ok(Derived::Key(DeriveKey::Decoder(repr))),
+            },
+            DeriveBuiltin::Hash => match hash::FlatHash::from_builtin_symbol(symbol)? {
+                FlatHash::SingleLambdaSetImmediate(imm) => {
+                    Ok(Derived::SingleLambdaSetImmediate(imm))
+                }
+                FlatHash::Key(repr) => Ok(Derived::Key(DeriveKey::Hash(repr))),
+            },
+            DeriveBuiltin::IsEq => {
+                // If obligation checking passes, we always lower derived implementations of `isEq`
+                // to the `Eq` low-level, to be fulfilled by the backends.
+                Ok(Derived::SingleLambdaSetImmediate(
+                    Symbol::BOOL_STRUCTURAL_EQ,
+                ))
+            }
+        }
+    }
 }

crates/compiler/mono/src/ir.rs

@@ -5331,7 +5331,7 @@ pub fn with_hole<'a>(
 
                                     let resolved_proc = match resolved_proc {
                                         Resolved::Specialization(symbol) => symbol,
-                                        Resolved::NeedsGenerated(_) => {
+                                        Resolved::Derive(_) => {
                                             todo_abilities!("Generate impls for structural types")
                                         }
                                     };
@@ -5813,14 +5813,7 @@ fn late_resolve_ability_specialization<'a>(
 
         match specialization {
             Resolved::Specialization(symbol) => symbol,
-            Resolved::NeedsGenerated(var) => {
+            Resolved::Derive(derive_key) => {
-                let derive_key = roc_derive_key::Derived::builtin(
-                    member.try_into().expect("derived symbols must be builtins"),
-                    env.subs,
-                    var,
-                )
-                .expect("specialization var not derivable!");
-
                 match derive_key {
                     roc_derive_key::Derived::Immediate(imm)
                     | roc_derive_key::Derived::SingleLambdaSetImmediate(imm) => {

crates/compiler/solve/src/ability.rs

@@ -4,8 +4,9 @@ use roc_collections::{VecMap, VecSet};
 use roc_debug_flags::dbg_do;
 #[cfg(debug_assertions)]
 use roc_debug_flags::ROC_PRINT_UNDERIVABLE;
+use roc_derive_key::Derived;
 use roc_error_macros::internal_error;
-use roc_module::symbol::Symbol;
+use roc_module::symbol::{ModuleId, Symbol};
 use roc_region::all::{Loc, Region};
 use roc_solve_problem::{
     NotDerivableContext, NotDerivableDecode, NotDerivableEncode, NotDerivableEq, TypeError,
@@ -1298,12 +1299,12 @@ pub fn type_implementing_specialization(
 }
 
 /// Result of trying to resolve an ability specialization.
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Debug)]
 pub enum Resolved {
     /// A user-defined specialization should be used.
     Specialization(Symbol),
-    /// A specialization must be generated for the given type variable.
+    /// A specialization must be generated with the given derive key.
-    NeedsGenerated(Variable),
+    Derive(Derived),
 }
 
 /// An [`AbilityResolver`] is a shell of an abilities store that answers questions needed for
@@ -1346,6 +1347,13 @@ impl AbilityResolver for AbilitiesStore {
     }
 }
 
+/// Whether this a module whose types' ability implementations should be checked via derive_key,
+/// because they do not explicitly list ability implementations due to circular dependencies.
+#[inline]
+pub(crate) fn builtin_module_with_unlisted_ability_impl(module_id: ModuleId) -> bool {
+    matches!(module_id, ModuleId::NUM | ModuleId::BOOL)
+}
+
 pub fn resolve_ability_specialization<R: AbilityResolver>(
     subs: &mut Subs,
     resolver: &R,
@@ -1379,6 +1387,17 @@ pub fn resolve_ability_specialization<R: AbilityResolver>(
 
     let resolved = match obligated {
         Obligated::Opaque(symbol) => {
+            if builtin_module_with_unlisted_ability_impl(symbol.module_id()) {
+                let derive_key = roc_derive_key::Derived::builtin_with_builtin_symbol(
+                    ability_member
+                        .try_into()
+                        .expect("derived symbols must be builtins"),
+                    symbol,
+                )
+                .expect("specialization var not derivable!");
+
+                Resolved::Derive(derive_key)
+            } else {
                 let impl_key = roc_can::abilities::ImplKey {
                     opaque: symbol,
                     ability_member,
@@ -1390,12 +1409,23 @@ pub fn resolve_ability_specialization<R: AbilityResolver>(
                     }
                     // TODO this is not correct. We can replace `Resolved` with `MemberImpl` entirely,
                     // which will make this simpler.
-                roc_types::types::MemberImpl::Error => Resolved::Specialization(Symbol::UNDERSCORE),
+                    roc_types::types::MemberImpl::Error => {
+                        Resolved::Specialization(Symbol::UNDERSCORE)
+                    }
+                }
             }
         }
         Obligated::Adhoc(variable) => {
-            // TODO: more rules need to be validated here, like is this a builtin ability?
+            let derive_key = roc_derive_key::Derived::builtin(
-            Resolved::NeedsGenerated(variable)
+                ability_member
+                    .try_into()
+                    .expect("derived symbols must be builtins"),
+                subs,
+                variable,
+            )
+            .expect("specialization var not derivable!");
+
+            Resolved::Derive(derive_key)
         }
     };
 

crates/compiler/solve/src/specialize.rs

@@ -24,7 +24,10 @@ use roc_types::{
 };
 use roc_unify::unify::{unify, Env as UEnv, Mode, MustImplementConstraints};
 
-use crate::solve::{deep_copy_var_in, introduce, Pools};
+use crate::{
+    ability::builtin_module_with_unlisted_ability_impl,
+    solve::{deep_copy_var_in, introduce, Pools},
+};
 
 /// What phase in the compiler is reaching out to specialize lambda sets?
 /// This is important to distinguish subtle differences in the behavior of the solving algorithm.
@@ -626,7 +629,7 @@ fn make_specialization_decision<P: Phase>(
     use SpecializationTypeKey::*;
     match subs.get_content_without_compacting(var) {
         Alias(opaque, _, _, AliasKind::Opaque)
-            if !matches!(opaque.module_id(), ModuleId::NUM | ModuleId::BOOL) =>
+            if !builtin_module_with_unlisted_ability_impl(opaque.module_id()) =>
         {
             if P::IS_LATE {
                 SpecializeDecision::Specialize(Opaque(*opaque))

crates/compiler/test_gen/src/gen_abilities.rs

@@ -504,6 +504,25 @@ mod encode_immediate {
         )
     }
 
+    #[test]
+    #[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
+    fn bool() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                app "test" imports [Encode, Json] provides [main] to "./platform"
+
+                main =
+                    when Str.fromUtf8 (Encode.toBytes Bool.false Json.toUtf8) is
+                        Ok s -> s
+                        _ -> "<bad>"
+                "#
+            ),
+            RocStr::from(r"false"),
+            RocStr
+        )
+    }
+
     macro_rules! num_immediate {
         ($($num:expr, $typ:ident)*) => {$(
             #[test]
@@ -1001,6 +1020,25 @@ mod decode_immediate {
         )
     }
 
+    #[test]
+    #[cfg(any(feature = "gen-llvm"))]
+    fn bool() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                app "test" imports [Json] provides [main] to "./platform"
+
+                main =
+                    when Str.toUtf8 "false" |> Decode.fromBytes Json.fromUtf8 is
+                        Ok s -> s
+                        _ -> Bool.true
+                "#
+            ),
+            false,
+            bool
+        )
+    }
+
     macro_rules! num_immediate {
         ($($num:expr, $typ:ident)*) => {$(
             #[test]