From 3224f1c3cd303ef1ed2ea13eb7a2ba4328a64ead Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 17 Sep 2023 17:45:02 +0100
Subject: Check target tuple has the right number of elements

---
 .../shedlang/compiler/typechecker/TypeChecker.java |  8 +++++++
 .../errors/TargetTupleHasWrongElementCount.java    | 23 +++++++++++++++++++
 .../typechecker/TypeCheckerAssignTests.java        | 26 ++++++++++++++++++++++
 3 files changed, 57 insertions(+)
 create mode 100644 src/main/java/org/shedlang/compiler/typechecker/errors/TargetTupleHasWrongElementCount.java

(limited to 'src')

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index 435de6de..ebdb7161 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -874,6 +874,14 @@ public class TypeChecker {
                     );
                 }
 
+                if (targetTuple.elements().size() != tupleType.elements().size()) {
+                    throw new TargetTupleHasWrongElementCount(
+                        tupleType.elements().size(),
+                        targetTuple.elements().size(),
+                        targetTuple.source()
+                    );
+                }
+
                 var typedTargetElements = new ArrayList<TypedTargetNode>();
 
                 for (var elementIndex = 0; elementIndex < targetTuple.elements().size(); elementIndex++) {
diff --git a/src/main/java/org/shedlang/compiler/typechecker/errors/TargetTupleHasWrongElementCount.java b/src/main/java/org/shedlang/compiler/typechecker/errors/TargetTupleHasWrongElementCount.java
new file mode 100644
index 00000000..da2d6ba9
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/errors/TargetTupleHasWrongElementCount.java
@@ -0,0 +1,23 @@
+package org.shedlang.compiler.typechecker.errors;
+
+import org.shedlang.compiler.errors.SourceError;
+import org.shedlang.compiler.sources.Source;
+
+public class TargetTupleHasWrongElementCount extends SourceError {
+    private final int expression;
+    private final int target;
+
+    public TargetTupleHasWrongElementCount(int expression, int target, Source source) {
+        super("Expression has " + expression + " elements, but target has " + target + " elements", source);
+        this.expression = expression;
+        this.target = target;
+    }
+
+    public int expression() {
+        return expression;
+    }
+
+    public int target() {
+        return target;
+    }
+}
diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerAssignTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerAssignTests.java
index b71db8f7..eb2a2db1 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerAssignTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerAssignTests.java
@@ -7,8 +7,10 @@ import org.shedlang.compiler.ast.untyped.Untyped;
 import org.shedlang.compiler.ast.untyped.UntypedFunctionStatementNode;
 import org.shedlang.compiler.ast.untyped.UntypedNamespaceStatementNode;
 import org.shedlang.compiler.typechecker.errors.CanOnlyAssignToVarError;
+import org.shedlang.compiler.typechecker.errors.TargetTupleHasWrongElementCount;
 import org.shedlang.compiler.typechecker.errors.UnexpectedTypeError;
 import org.shedlang.compiler.typechecker.typesets.TypeSets;
+import org.shedlang.compiler.types.TupleType;
 import org.shedlang.compiler.types.Types;
 import org.shedlang.compiler.util.P;
 
@@ -123,6 +125,30 @@ public class TypeCheckerAssignTests {
         assertThat(error.expected(), equalTo(TypeSets.TUPLE));
     }
 
+    @Test
+    public void whenExpressionAndTargetAreTuplesWithDifferentElementCountThenErrorIsThrown() {
+        var untyped = Untyped.assign(
+            Untyped.targetTuple(List.of(
+                Untyped.targetVal("a"),
+                Untyped.targetVal("b")
+            )),
+            Untyped.reference("x")
+        );
+        var tupleType = new TupleType(List.of(Types.STRING));
+        var context = TypeCheckerContext.EMPTY
+            .enterNamespace(P.map(
+                Map.entry("x", Variable.defined(tupleType, VariableType.VAL))
+            ));
+
+        var error = assertThrows(
+            TargetTupleHasWrongElementCount.class,
+            () -> typeCheckFunctionStatement(untyped, context)
+        );
+
+        assertThat(error.expression(), equalTo(1));
+        assertThat(error.target(), equalTo(2));
+    }
+
     private static TypeCheckerResult<? extends TypedFunctionStatementNode> typeCheckFunctionStatement(
         UntypedFunctionStatementNode untyped,
         TypeCheckerContext context
-- 
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