Add options to the StructurizrDslParser to be able to inject some par…

…sing behaviors.

The only option is to force unique constant declaration, in order to prevent constants override inside a workspace.

structurizr-dsl/build.gradle

@@ -9,6 +9,7 @@ dependencies {
 
     testImplementation 'org.junit.jupiter:junit-jupiter-engine:5.9.2'
     testImplementation 'org.junit.jupiter:junit-jupiter-params:5.9.2'
+    testImplementation 'org.assertj:assertj-core:3.24.2'
 }
 
 description = 'Structurizr DSL'

structurizr-dsl/src/main/java/com/structurizr/dsl/StructurizrDslParser.java

@@ -43,6 +43,7 @@ public final class StructurizrDslParser extends StructurizrDslTokens {
     private final Set<String> parsedTokens = new HashSet<>();
     private final IdentifiersRegister identifiersRegister;
     private final Map<String, Constant> constants;
+    private final StructurizrDslParserOptions parserOptions;
 
     private final List<String> dslSourceLines = new ArrayList<>();
     private Workspace workspace;
@@ -54,9 +55,14 @@ public final class StructurizrDslParser extends StructurizrDslTokens {
      * Creates a new instance of the parser.
      */
     public StructurizrDslParser() {
+        this(new StructurizrDslParserOptions(false));
+    }
+
+    public StructurizrDslParser(StructurizrDslParserOptions options) {
         contextStack = new Stack<>();
         identifiersRegister = new IdentifiersRegister();
         constants = new HashMap<>();
+        parserOptions = options;
     }
 
     /**
@@ -874,7 +880,11 @@ void parse(List<String> lines, File dslFile, boolean include) throws Structurizr
                     } else if (CONSTANT_TOKEN.equalsIgnoreCase(firstToken)) {
                         Constant constant = new ConstantParser().parse(getContext(), tokens);
                         if (constants.containsKey(constant.getName())) {
-                            log.warn("A constant named " + constant.getName() + " already exists");
+                            String message = "A constant named " + constant.getName() + " already exists";
+                            if(parserOptions.uniqueConstantsDeclaration()) {
+                                throw new StructurizrDslParserException(message);
+                            }
+                            log.warn(message);
                         }
                         constants.put(constant.getName(), constant);
 

structurizr-dsl/src/main/java/com/structurizr/dsl/StructurizrDslParserOptions.java

@@ -0,0 +1,9 @@
+package com.structurizr.dsl;
+
+/**
+ * @param uniqueConstantsDeclaration If set to true, then constants declared with the !constant keyword cannot be overridden.
+ */
+public record StructurizrDslParserOptions(
+        boolean uniqueConstantsDeclaration
+) {
+}

structurizr-dsl/src/test/java/com/structurizr/dsl/UniqueConstantsConfigurationTests.java

@@ -0,0 +1,26 @@
+package com.structurizr.dsl;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThatCode;
+
+public class UniqueConstantsConfigurationTests {
+
+    @Test
+    void shouldFailOnConstantDuplication() {
+        String dsl = """
+                    workspace {
+                        !constant NAME toto
+                        !constant NAME titi
+                    }
+                """;
+
+        StructurizrDslParser parser = new StructurizrDslParser(
+                new StructurizrDslParserOptions(true)
+        );
+
+        assertThatCode(() -> parser.parse(dsl))
+                .isInstanceOf(StructurizrDslParserException.class)
+                .hasMessageStartingWith("A constant named NAME already exists");
+    }
+}