Fix off by one issue (#101)

* Fix off by one issue

* Check location and add issue link

* Inline file into test

* Clear blank line

* Avoid all-star import

Author: kubukoz

src/main/java/software/amazon/smithy/lsp/ext/FileCachingCollector.java

@@ -274,7 +274,9 @@ private Boolean shapeWasDefinedInline(OperationShape operation, Shape shape, Mod
         }
         int boundary = Math.max(priorShapeLine, operation.getSourceLocation().getLine());
         while (shapeStartLine >= boundary) {
-            String line = modelFile.lines.get(shapeStartLine);
+            String line = modelFile.lines.get(shapeStartLine - 1);
+
+            // note: this doesn't take code inside comments into account
             if (line.contains(":=")) {
                 return true;
             }

src/test/java/software/amazon/smithy/lsp/ext/SmithyProjectTest.java

@@ -15,9 +15,6 @@
 
 package software.amazon.smithy.lsp.ext;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-
 import java.io.File;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -43,6 +40,10 @@
 import software.amazon.smithy.utils.ListUtils;
 import software.amazon.smithy.utils.MapUtils;
 
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+
 public class SmithyProjectTest {
 
     @Test
@@ -124,6 +125,30 @@ public void ignoresUnmodeledApplyStatements() throws Exception {
         }
     }
 
+    // https://github.com/awslabs/smithy-language-server/issues/100
+    @Test
+    public void allowsEmptyStructsWithMixins() throws Exception {
+        String fileText = "$version: \"2\"\n" +
+                "\n" +
+                "namespace demo\n" +
+                "\n" +
+                "operation MyOp {\n" +
+                "    output: MyOpOutput\n" +
+                "}\n" +
+                "\n" +
+                "@output\n" +
+                "structure MyOpOutput {}\n";
+
+        Map<String, String> files = MapUtils.of("main.smithy", fileText);
+
+        try (Harness hs = Harness.create(SmithyBuildExtensions.builder().build(), files)) {
+            assertNotNull(hs.getProject());
+            Map<ShapeId, Location> locationMap = hs.getProject().getLocations();
+
+            correctLocation(locationMap, "demo#MyOpOutput", 9, 0, 9, 23);
+        }
+    }
+
     @Test
     public void definitionLocationsV1() throws Exception {
         Path baseDir = Paths.get(SmithyProjectTest.class.getResource("models/v1").toURI());