feat(language): validate assignment expressions

1 files changed, 32 insertions, 0 deletions

diff --git a/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java b/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java
index 560f612a..7f45bc20 100644
--- a/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java
+++ b/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java
@@ -63,6 +63,8 @@ public class ProblemValidator extends AbstractProblemValidator {
 
         public static final String UNSUPPORTED_ASSERTION_ISSUE = ISSUE_PREFIX + "UNSUPPORTED_ASSERTION";
 
+        public static final String INVALID_ASSIGNMENT_ISSUE = ISSUE_PREFIX + "INVALID_ASSIGNMENT";
+
         @Inject
         private ReferenceCounter referenceCounter;
 
@@ -493,4 +495,34 @@ public class ProblemValidator extends AbstractProblemValidator {
                         }
                 }
         }
+
+        @Check
+        private void checkAssignmentExpr(AssignmentExpr assignmentExpr) {
+                var left = assignmentExpr.getLeft();
+                if (left == null) {
+                        // Syntactically invalid, so we already emit an error.
+                        return;
+                }
+                if (!(left instanceof VariableOrNodeExpr variableOrNodeExpr)) {
+                        var message = "Left side of an assignment must be variable.";
+                        acceptError(message, assignmentExpr, ProblemPackage.Literals.BINARY_EXPR__LEFT,
+                                        0, INVALID_ASSIGNMENT_ISSUE);
+                        return;
+                }
+                var target = variableOrNodeExpr.getVariableOrNode();
+                if (target == null) {
+                        // Syntactically invalid, so we already emit an error.
+                        return;
+                }
+                if (target instanceof Parameter) {
+                        var message = "Parameters cannot be assigned.";
+                        acceptError(message, variableOrNodeExpr, ProblemPackage.Literals.VARIABLE_OR_NODE_EXPR__VARIABLE_OR_NODE,
+                                        0, INVALID_ASSIGNMENT_ISSUE);
+                }
+                if (target instanceof Node) {
+                        var message = "Nodes cannot be assigned.";
+                        acceptError(message, variableOrNodeExpr, ProblemPackage.Literals.VARIABLE_OR_NODE_EXPR__VARIABLE_OR_NODE,
+                                        0, INVALID_ASSIGNMENT_ISSUE);
+                }
+        }
 }