From d1d9c3800ab56b3c825f72e3e997b0521cfac9ce Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sat, 10 Jun 2023 11:36:34 +0100
Subject: Check named arg is not passed twice

---
 .../org/shedlang/compiler/typechecker/TypeChecker.java  | 16 ++++++++++++----
 .../errors/CannotPassNamedArgTwiceError.java            | 17 +++++++++++++++++
 2 files changed, 29 insertions(+), 4 deletions(-)
 create mode 100644 src/main/java/org/shedlang/compiler/typechecker/errors/CannotPassNamedArgTwiceError.java

(limited to 'src/main/java')

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index edfb961c..11f902b1 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -7,6 +7,8 @@ import org.shedlang.compiler.typechecker.typesets.TypeSets;
 import org.shedlang.compiler.types.FunctionType;
 import org.shedlang.compiler.types.Type;
 
+import java.util.HashSet;
+
 public class TypeChecker {
     private TypeChecker() {
     }
@@ -57,6 +59,7 @@ public class TypeChecker {
             checkExpressionType(typedArg, paramType, context);
         }
 
+        var seenNamedArgNames = new HashSet<String>();
         for (var typedArg : typedNamedArgs) {
             var param = receiverType.namedParams().stream()
                 .filter(namedParam -> namedParam.name().equals(typedArg.name()))
@@ -64,13 +67,18 @@ public class TypeChecker {
                 .orElseThrow(() -> new UnexpectedNamedArgError(typedArg.name(), typedArg.source()));
 
             checkExpressionType(typedArg.expression(), param.type(), context);
+
+            if (seenNamedArgNames.contains(typedArg.name())) {
+                throw new CannotPassNamedArgTwiceError(typedArg.name(), typedArg.source());
+            }
+
+            seenNamedArgNames.add(typedArg.name());
         }
 
         for (var namedParam : receiverType.namedParams()) {
-            typedNamedArgs.stream()
-                .filter(namedArg -> namedArg.name().equals(namedParam.name()))
-                .findFirst()
-                .orElseThrow(() -> new MissingNamedArgError(namedParam.name(), args.source()));
+            if (!seenNamedArgNames.contains(namedParam.name())) {
+                throw new MissingNamedArgError(namedParam.name(), args.source());
+            }
         }
 
         return new TypedArgsNode(typedPositionalArgs, typedNamedArgs, args.source());
diff --git a/src/main/java/org/shedlang/compiler/typechecker/errors/CannotPassNamedArgTwiceError.java b/src/main/java/org/shedlang/compiler/typechecker/errors/CannotPassNamedArgTwiceError.java
new file mode 100644
index 00000000..168d46de
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/errors/CannotPassNamedArgTwiceError.java
@@ -0,0 +1,17 @@
+package org.shedlang.compiler.typechecker.errors;
+
+import org.shedlang.compiler.errors.SourceError;
+import org.shedlang.compiler.sources.Source;
+
+public class CannotPassNamedArgTwiceError extends SourceError {
+    private final String argName;
+
+    public CannotPassNamedArgTwiceError(String argName, Source source) {
+        super("Cannot pass named arg " + argName + " twice", source);
+        this.argName = argName;
+    }
+
+    public String argName() {
+        return argName;
+    }
+}
-- 
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