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Fix type checking around comprehensions with empty iteration range #2263

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Merged
copybara-service merged 1 commit into from
Sep 11, 2026
Merged

Fix type checking around comprehensions with empty iteration range #2263

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10 changes: 9 additions & 1 deletion checker/internal/type_checker_impl.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -838,7 +838,8 @@ void ResolveVisitor::PostVisitComprehensionSubexpression(
GetDeducedType(&comprehension.accu_init())));
break;
case ComprehensionArg::ITER_RANGE: {
Type range_type = GetDeducedType(&comprehension.iter_range());
Type range_type = inference_context_->FullySubstitute(
GetDeducedType(&comprehension.iter_range()), /*free_to_dyn=*/false);
Type iter_type = DynType(); // iter_var for non comprehensions v2.
Type iter_type1 = DynType(); // iter_var for comprehensions v2.
Type iter_type2 = DynType(); // iter_var2 for comprehensions v2.
Expand All @@ -851,7 +852,14 @@ void ResolveVisitor::PostVisitComprehensionSubexpression(
iter_type = iter_type1 = range_type.GetMap().key();
iter_type2 = range_type.GetMap().value();
break;
case TypeKind::kTypeParam:
// Set the range type to DYN to prevent assignment to a potentially
// incorrect type at a later point in type-checking. The IsAssignable
// call will update the type substitutions for the type param.
inference_context_->IsAssignable(DynType(), range_type);
break;
case TypeKind::kDyn:
case TypeKind::kError:
break;
default:
ReportIssue(TypeCheckIssue::CreateError(
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70 changes: 70 additions & 0 deletions checker/internal/type_checker_impl_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1287,6 +1287,76 @@ TEST(TypeCheckerImplTest, ComprehensionDynRange) {
EXPECT_THAT(result.GetIssues(), IsEmpty());
}

TEST(TypeCheckerImplTest, EmptyListRangeNestedListComprehension) {
TypeCheckEnv env(GetSharedTestingDescriptorPool());
google::protobuf::Arena arena;
ASSERT_THAT(RegisterMinimalBuiltins(&arena, env), IsOk());

TypeCheckerImpl impl(std::move(env));
ASSERT_OK_AND_ASSIGN(auto ast, MakeTestParsedAst("[].map(x, x.map(y, y))"));
ASSERT_OK_AND_ASSIGN(ValidationResult result, impl.Check(std::move(ast)));

EXPECT_TRUE(result.IsValid()) << result.FormatError();
EXPECT_THAT(result.GetIssues(), IsEmpty());

ASSERT_OK_AND_ASSIGN(auto checked_ast, result.ReleaseAst());
EXPECT_EQ(checked_ast->GetReturnType(),
AstType(ListTypeSpec(std::make_unique<AstType>(
ListTypeSpec(std::make_unique<AstType>(DynTypeSpec()))))));
}

TEST(TypeCheckerImplTest, EmptyMapRangeNestedComprehension) {
TypeCheckEnv env(GetSharedTestingDescriptorPool());
google::protobuf::Arena arena;
ASSERT_THAT(RegisterMinimalBuiltins(&arena, env), IsOk());

TypeCheckerImpl impl(std::move(env));
ASSERT_OK_AND_ASSIGN(auto ast, MakeTestParsedAst("{}.map(k, k.map(y, y))"));
ASSERT_OK_AND_ASSIGN(ValidationResult result, impl.Check(std::move(ast)));

EXPECT_TRUE(result.IsValid()) << result.FormatError();
EXPECT_THAT(result.GetIssues(), IsEmpty());

ASSERT_OK_AND_ASSIGN(auto checked_ast, result.ReleaseAst());
EXPECT_EQ(checked_ast->GetReturnType(),
AstType(ListTypeSpec(std::make_unique<AstType>(
ListTypeSpec(std::make_unique<AstType>(DynTypeSpec()))))));
}

TEST(TypeCheckerImplTest, EmptyRangeNestedComprehensionPredicate) {
TypeCheckEnv env(GetSharedTestingDescriptorPool());
google::protobuf::Arena arena;
ASSERT_THAT(RegisterMinimalBuiltins(&arena, env), IsOk());

TypeCheckerImpl impl(std::move(env));
ASSERT_OK_AND_ASSIGN(auto ast,
MakeTestParsedAst("[].all(x, x.all(y, y == 1))"));
ASSERT_OK_AND_ASSIGN(ValidationResult result, impl.Check(std::move(ast)));

EXPECT_TRUE(result.IsValid()) << result.FormatError();
EXPECT_THAT(result.GetIssues(), IsEmpty());

ASSERT_OK_AND_ASSIGN(auto checked_ast, result.ReleaseAst());
EXPECT_EQ(checked_ast->GetReturnType(), AstType(PrimitiveType::kBool));
}

TEST(TypeCheckerImplTest, EmptyRangeNestedComprehensionBeforeConstraint) {
TypeCheckEnv env(GetSharedTestingDescriptorPool());
google::protobuf::Arena arena;
ASSERT_THAT(RegisterMinimalBuiltins(&arena, env), IsOk());

TypeCheckerImpl impl(std::move(env));
ASSERT_OK_AND_ASSIGN(
auto ast, MakeTestParsedAst("[].all(x, x.all(y, y == 1) && x == 1)"));
ASSERT_OK_AND_ASSIGN(ValidationResult result, impl.Check(std::move(ast)));

EXPECT_TRUE(result.IsValid()) << result.FormatError();
EXPECT_THAT(result.GetIssues(), IsEmpty());

ASSERT_OK_AND_ASSIGN(auto checked_ast, result.ReleaseAst());
EXPECT_EQ(checked_ast->GetReturnType(), AstType(PrimitiveType::kBool));
}

TEST(TypeCheckerImplTest, BasicOvlResolution) {
TypeCheckEnv env(GetSharedTestingDescriptorPool());
google::protobuf::Arena arena;
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