Type check resume statements properly

4 files changed, 122 insertions, 2 deletions

diff --git a/src/test/java/org/shedlang/compiler/ast/untyped/Untyped.java b/src/test/java/org/shedlang/compiler/ast/untyped/Untyped.java
index adae966a..51b6c2b6 100644
--- a/src/test/java/org/shedlang/compiler/ast/untyped/Untyped.java
+++ b/src/test/java/org/shedlang/compiler/ast/untyped/Untyped.java
@@ -157,6 +157,10 @@ public class Untyped {
         return new UntypedResumeNode(Optional.empty(), Sources.NULL);
     }
 
+    public static UntypedResumeNode resume(UntypedExpressionNode expression) {
+        return new UntypedResumeNode(Optional.of(expression), Sources.NULL);
+    }
+
     public static UntypedStringLiteralNode stringLiteral(String value) {
         return new UntypedStringLiteralNode(value, Sources.NULL);
     }
diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionResumeTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionResumeTests.java
new file mode 100644
index 00000000..c3326020
--- /dev/null
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionResumeTests.java
@@ -0,0 +1,116 @@
+package org.shedlang.compiler.typechecker;
+
+import org.junit.jupiter.api.Test;
+import org.shedlang.compiler.ast.untyped.Untyped;
+import org.shedlang.compiler.ast.untyped.UntypedFunctionExpressionNode;
+import org.shedlang.compiler.typechecker.errors.CannotResumeOutsideOfEffectHandlerFieldError;
+import org.shedlang.compiler.typechecker.errors.UnexpectedTypeError;
+import org.shedlang.compiler.typechecker.typesets.TypeSets;
+import org.shedlang.compiler.types.Effects;
+import org.shedlang.compiler.types.FunctionType;
+import org.shedlang.compiler.types.NamespaceName;
+import org.shedlang.compiler.types.Types;
+import org.shedlang.compiler.util.P;
+
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.shedlang.compiler.ast.typed.TypedNodeMatchers.*;
+import static org.zwobble.precisely.AssertThat.assertThat;
+import static org.zwobble.precisely.Matchers.equalTo;
+
+public class TypeCheckerFunctionResumeTests {
+    @Test
+    public void expressionIsTypeChecked() {
+        var untyped = Untyped.resume(Untyped.stringLiteral("hello"));
+        var context = TypeCheckerContext.EMPTY
+            .enterFunction(P.map(), Effects.NONE, ReturnTypeState.effectHandler(Types.STRING));
+
+        var typed = TypeChecker.typeCheckFunctionStatement(untyped, context);
+
+        assertThat(typed.value(), isTypedResumeNode(isTypedStringLiteralNode("hello")));
+    }
+
+    @Test
+    public void whenExpressionIsAbsentThenUnitIsReturned() {
+        var untyped = Untyped.resume();
+        var context = TypeCheckerContext.EMPTY
+            .enterFunction(P.map(), Effects.NONE, ReturnTypeState.effectHandler(Types.UNIT));
+
+        var typed = TypeChecker.typeCheckFunctionStatement(untyped, context);
+
+        assertThat(typed.value(), isTypedResumeNode(isTypedUnitLiteralNode()));
+    }
+
+    @Test
+    public void whenNotInFunctionThenResumeIsForbidden() {
+        var untyped = Untyped.resume(Untyped.stringLiteral("hello"));
+        var context = TypeCheckerContext.EMPTY
+            .enterNamespace(NamespaceName.of("Example"), P.map());
+
+        assertThrows(
+            CannotResumeOutsideOfEffectHandlerFieldError.class,
+            () -> TypeChecker.typeCheckFunctionStatement(untyped, context)
+        );
+    }
+
+    @Test
+    public void whenInFunctionThenResumeIsForbidden() {
+        var untyped = Untyped.resume(Untyped.stringLiteral("hello"));
+        var context = TypeCheckerContext.EMPTY
+            .enterFunction(P.map(), Effects.NONE, ReturnTypeState.explicit(Types.STRING));
+
+        assertThrows(
+            CannotResumeOutsideOfEffectHandlerFieldError.class,
+            () -> TypeChecker.typeCheckFunctionStatement(untyped, context)
+        );
+    }
+
+    @Test
+    public void canResumeWIthSubtypeOfResumeType() {
+        var untyped = Untyped.resume(Untyped.stringLiteral("hello"));
+        var context = TypeCheckerContext.EMPTY
+            .enterFunction(P.map(), Effects.NONE, ReturnTypeState.effectHandler(Types.TOP));
+
+        var typed = TypeChecker.typeCheckFunctionStatement(untyped, context);
+
+        assertThat(typed.value(), isTypedResumeNode(isTypedStringLiteralNode("hello")));
+    }
+
+    @Test
+    public void cannotResumeWithNonSubtypeOfResumeType() {
+        var untyped = Untyped.resume(Untyped.stringLiteral("hello"));
+        var context = TypeCheckerContext.EMPTY
+            .enterFunction(P.map(), Effects.NONE, ReturnTypeState.effectHandler(Types.INT));
+
+        var error = assertThrows(
+            UnexpectedTypeError.class,
+            () -> TypeChecker.typeCheckFunctionStatement(untyped, context)
+        );
+
+        assertThat(error.expected(), equalTo(TypeSets.type(Types.INT)));
+        assertThat(error.actual(), equalTo(Types.STRING));
+    }
+
+    @Test
+    public void resumeTypeIsUsedAsTypeHintForExpression() {
+        var untyped = Untyped.resume(
+            UntypedFunctionExpressionNode.builder()
+                .addPositionalParam("x", Optional.empty())
+                .withoutReturnType()
+                .build()
+        );
+        var resumeType = FunctionType.builder()
+            .addPositionalParam(Types.STRING)
+            .withReturnType(Types.UNIT)
+            .build();
+        var context = TypeCheckerContext.EMPTY
+            .enterFunction(P.map(), Effects.NONE, ReturnTypeState.effectHandler(resumeType));
+
+        var typed = TypeChecker.typeCheckFunctionStatement(untyped, context);
+
+        assertThat(typed.value(), isTypedResumeNode(
+            isTypedFunctionExpressionNode().withType(resumeType)
+        ));
+    }
+}
diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionReturnTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionReturnTests.java
index f0c2daa7..8fe03d32 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionReturnTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionReturnTests.java
@@ -59,7 +59,7 @@ public class TypeCheckerFunctionReturnTests {
     public void whenInEffectHandlerThenReturnIsForbidden() {
         var untyped = Untyped.functionReturn(Untyped.stringLiteral("hello"));
         var context = TypeCheckerContext.EMPTY
-            .enterFunction(P.map(), Effects.NONE, ReturnTypeState.effectHandler(Types.UNIT));
+            .enterFunction(P.map(), Effects.NONE, ReturnTypeState.effectHandler(Types.STRING));
 
         assertThrows(
             CannotReturnFromEffectHandlerFieldError.class,
diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerTryTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerTryTests.java
index cffae60a..169816dc 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerTryTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerTryTests.java
@@ -366,7 +366,7 @@ public class TypeCheckerTryTests {
             .addHandlerField(
                 UntypedFunctionDefinitionNode.builder()
                     .withName("effectField")
-                    .addStatement(Untyped.expressionStatement(
+                    .addStatement(Untyped.resume(
                         UntypedCallNode.builder()
                             .withReceiver(Untyped.reference("f"))
                             .withHasEffects(true)