[validation] add error if path do not start with a slash

modules/openapi-generator-cli/src/main/java/org/openapitools/codegen/cmd/Validate.java

@@ -46,6 +46,7 @@ public void run() {
         SwaggerParseResult result = new OpenAPIParser().readLocation(spec, null, null);
         List<String> messageList = result.getMessages();
         Set<String> errors = new HashSet<String>(messageList);
+        errors.addAll(ModelUtils.getErrorMessages(result.getOpenAPI()));
         Set<String> warnings = new HashSet<String>();
 
         StringBuilder sb = new StringBuilder();

modules/openapi-generator/src/main/java/org/openapitools/codegen/config/CodegenConfigurator.java

@@ -543,6 +543,7 @@ public ClientOptInput toClientOptInput() {
 
         Set<String> validationMessages = new HashSet<>(result.getMessages());
         OpenAPI specification = result.getOpenAPI();
+        validationMessages.addAll(ModelUtils.getErrorMessages(specification));
 
         // NOTE: We will only expose errors+warnings if there are already errors in the spec.
         if (validationMessages.size() > 0) {

modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java

@@ -53,6 +53,7 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.stream.Collectors;
@@ -692,4 +693,21 @@ public static Header getHeader(OpenAPI openAPI, String name) {
         }
         return null;
     }
+
+    /**
+     * Compute additional error messages that are not detected by the parser
+     * @param openAPI specification being checked
+     * @return a list of errors (items that are not conform)
+     */
+    public static List<String> getErrorMessages(OpenAPI openAPI) {
+        List<String> errors = new ArrayList<>();
+        if (openAPI.getPaths() != null) {
+            List<String> pathErrors = openAPI.getPaths().keySet().stream()
+                .filter(path -> !path.startsWith("/"))
+                .map(path -> String.format(Locale.ROOT, "'%s' must begin with a slash, change it to '/%s'", path, path))
+                .collect(Collectors.toList());
+            errors.addAll(pathErrors);
+        }
+        return errors;
+    }
 }

modules/openapi-generator/src/test/java/org/openapitools/codegen/utils/ModelUtilsTest.java

@@ -19,10 +19,13 @@
 
 import io.swagger.parser.OpenAPIParser;
 import io.swagger.v3.oas.models.OpenAPI;
+import io.swagger.v3.oas.models.Operation;
+import io.swagger.v3.oas.models.PathItem;
 import io.swagger.v3.oas.models.media.*;
 import io.swagger.v3.oas.models.parameters.Parameter;
 import io.swagger.v3.oas.models.parameters.RequestBody;
 import io.swagger.v3.oas.models.responses.ApiResponse;
+import io.swagger.v3.oas.models.responses.ApiResponses;
 import io.swagger.v3.parser.core.models.ParseOptions;
 
 import org.openapitools.codegen.TestUtils;
@@ -193,4 +196,25 @@ public void testComposedSchemasAreNotUnaliased() {
 
         Assert.assertEquals(refToComposedSchema, ModelUtils.unaliasSchema(allSchemas, refToComposedSchema));
     }
+
+    @Test
+    public void testGetErrorMessages() {
+        //empty case:
+        OpenAPI openAPI1 = TestUtils.createOpenAPI();
+        List<String> errors1 = ModelUtils.getErrorMessages(openAPI1);
+        Assert.assertEquals(errors1.size(), 0);
+
+        //wrong path:
+        OpenAPI openAPI2 = TestUtils.createOpenAPI();
+        openAPI2.path("some/path", new PathItem().get(new Operation().operationId("op1").responses(new ApiResponses().addApiResponse("201", new ApiResponse().description("OK")))));
+        List<String> errors2 = ModelUtils.getErrorMessages(openAPI2);
+        Assert.assertEquals(errors2.size(), 1);
+        Assert.assertEquals(errors2.get(0), "'some/path' must begin with a slash, change it to '/some/path'");
+
+        //correct path:
+        OpenAPI openAPI3 = TestUtils.createOpenAPI();
+        openAPI3.path("/path2", new PathItem().get(new Operation().operationId("op1").responses(new ApiResponses().addApiResponse("201", new ApiResponse().description("OK")))));
+        List<String> errors3 = ModelUtils.getErrorMessages(openAPI3);
+        Assert.assertEquals(errors3.size(), 0);
+    }
 }