Added better support for concrete trait by output type.

Author: orizi

crates/cairo-lang-semantic/src/expr/inference.rs

@@ -913,29 +913,34 @@ impl<'db> Inference<'db> {
         let concrete_trait_id = self.rewrite(concrete_trait_id).no_err();
         enrich_lookup_context(self.db, concrete_trait_id, &mut lookup_context);
 
-        // Don't try to resolve impls if the first generic param is a variable.
-        let generic_args = concrete_trait_id.generic_args(self.db);
-        match generic_args.first() {
-            Some(GenericArgumentId::Type(ty)) => {
-                if let TypeLongId::Var(_) = ty.lookup_intern(self.db) {
-                    // Don't try to infer such impls.
-                    return Ok(SolutionSet::Ambiguous(Ambiguity::WillNotInfer(concrete_trait_id)));
+        // If has any type assignments, we can try to resolve it, even if first generic arg is a
+        // var.
+        if !impl_var_trait_item_mappings
+            .types
+            .iter()
+            .any(|(_, ty)| ty.is_var_free(self.db) && !ty.is_missing(self.db))
+        {
+            // Don't try to resolve impls if the first generic param is a variable.
+            let dont_infer = Ok(SolutionSet::Ambiguous(Ambiguity::WillNotInfer(concrete_trait_id)));
+            match concrete_trait_id.generic_args(self.db).first() {
+                Some(GenericArgumentId::Type(ty))
+                    if matches!(ty.lookup_intern(self.db), TypeLongId::Var(_)) =>
+                {
+                    return dont_infer;
                 }
-            }
-            Some(GenericArgumentId::Impl(imp)) => {
-                // Don't try to infer such impls.
-                if let ImplLongId::ImplVar(_) = imp.lookup_intern(self.db) {
-                    return Ok(SolutionSet::Ambiguous(Ambiguity::WillNotInfer(concrete_trait_id)));
+                Some(GenericArgumentId::Impl(imp))
+                    if matches!(imp.lookup_intern(self.db), ImplLongId::ImplVar(_)) =>
+                {
+                    return dont_infer;
                 }
-            }
-            Some(GenericArgumentId::Constant(const_value)) => {
-                if let ConstValue::Var(_, _) = const_value.lookup_intern(self.db) {
-                    // Don't try to infer such impls.
-                    return Ok(SolutionSet::Ambiguous(Ambiguity::WillNotInfer(concrete_trait_id)));
+                Some(GenericArgumentId::Constant(const_value))
+                    if matches!(const_value.lookup_intern(self.db), ConstValue::Var(_, _)) =>
+                {
+                    return dont_infer;
                 }
+                _ => {}
             }
-            _ => {}
-        };
+        }
         let (canonical_trait, canonicalizer) = CanonicalTrait::canonicalize(
             self.db,
             self.inference_id,

crates/cairo-lang-semantic/src/expr/test_data/closure

@@ -390,7 +390,7 @@ fn baz<T, +core::ops::FnOnce<T, (u32,)>>(c: T) -> core::ops::FnOnce::<T, (u32,)>
 }
 
 //! > expected_diagnostics
-error: Trait has no implementation in context: core::ops::function::Fn::<core::felt252, ()>.
+error: Inference cycle detected
  --> lib.cairo:7:19
     let _x: u32 = bar();
                   ^^^^^

crates/cairo-lang-semantic/src/expr/test_data/inference

@@ -755,3 +755,26 @@ error: Type annotations needed. Failed to infer ?0.
  --> lib.cairo:1:13
 fn foo() -> Option {
             ^^^^^^
+
+//! > ==========================================================================
+
+//! > Impl resolution by type.
+
+//! > test_runner_name
+test_function_diagnostics(expect_diagnostics: false)
+
+//! > function
+fn foo() {
+    let _u32: u32 = 2.pow(5);
+    const _U32: u32 = 2.pow(5);
+    let _felt252: felt252 = 2.pow(5);
+    const _FELT252: felt252 = 2.pow(5);
+}
+
+//! > function_name
+foo
+
+//! > module_code
+use core::num::traits::Pow;
+
+//! > expected_diagnostics