#237 better error message when a template is not found through Direct…

…oryCodeResolver

jte-runtime/src/main/java/gg/jte/CodeResolver.java

@@ -16,6 +16,24 @@ public interface CodeResolver {
      */
     String resolve(String name);
 
+    /**
+     * Resolves the code of a template, which is required to exist.
+     * @param name The name of the template, e.g. <code>"tag/util/card.jte"</code>.
+     * @return The code of the resolved template, this is never <code>null</code>.
+     * @throws TemplateNotFoundException if no template with this name exists.
+     *
+     * Implementations that have better knowledge why the loading failed, are expected to
+     * override this method and provide information about the problem in the thrown exception message.
+     */
+    default String resolveRequired(String name) throws TemplateNotFoundException {
+        String code = resolve(name);
+        if (code == null) {
+            throw new TemplateNotFoundException(name + " not found");
+        }
+
+        return code;
+    }
+
     /**
      * Resolves the last modification time of a template.
      * @param name The name of the template, e.g. <code>"tag/util/card.jte"</code>.

jte/src/main/java/gg/jte/compiler/TemplateCompiler.java

@@ -288,15 +288,15 @@ private CodeGenerator createCodeGenerator(ClassInfo classInfo, LinkedHashSet<Cla
     }
 
     private String resolveCode(String name, DebugInfo debugInfo) {
-        String code = codeResolver.resolve(name);
-        if (code == null) {
-            String message = name + " not found";
+        try {
+            return codeResolver.resolveRequired(name);
+        } catch (TemplateNotFoundException e) {
+            String message = e.getMessage();
             if (debugInfo != null) {
                 message += ", referenced at " + debugInfo.name + ":" + debugInfo.line;
             }
             throw new TemplateNotFoundException(message);
         }
-        return code;
     }
 
     @Override

jte/src/main/java/gg/jte/resolve/DirectoryCodeResolver.java

@@ -1,6 +1,7 @@
 package gg.jte.resolve;
 
 import gg.jte.CodeResolver;
+import gg.jte.TemplateNotFoundException;
 import gg.jte.compiler.IoUtils;
 
 import java.io.IOException;
@@ -24,10 +25,20 @@ public DirectoryCodeResolver(Path root) {
     @Override
     public String resolve(String name) {
         try {
-            Path file = root.resolve(name);
+            return resolveRequired(name);
+        } catch (TemplateNotFoundException e) {
+            return null;
+        }
+    }
+
+    @Override
+    public String resolveRequired(String name) throws TemplateNotFoundException {
+        Path file = root.resolve(name);
+
+        try {
             return Files.readString(file, StandardCharsets.UTF_8);
         } catch (NoSuchFileException e) {
-            return null;
+            throw new TemplateNotFoundException(name + " not found (tried to load file at " + file.toAbsolutePath() + ")");
         } catch (IOException e) {
             throw new UncheckedIOException(e);
         }

jte/src/test/java/gg/jte/TemplateEngine_HasTemplate_DirectoryCodeResolverTest.java

@@ -7,6 +7,7 @@
 import java.nio.file.Paths;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.catchThrowable;
 
 public class TemplateEngine_HasTemplate_DirectoryCodeResolverTest {
 
@@ -29,4 +30,13 @@ void templateExists() {
         assertThat(codeResolver.exists("welcome.jte")).isTrue();
         assertThat(templateEngine.hasTemplate("welcome.jte")).isTrue();
     }
+
+    @Test
+    void resolveRequired() {
+        Throwable throwable = catchThrowable(() -> codeResolver.resolveRequired("does-not-exist.jte"));
+
+        assertThat(throwable).isInstanceOf(TemplateNotFoundException.class)
+                .hasMessageStartingWith("does-not-exist.jte not found (tried to load file at ")
+                .hasMessageEndingWith("does-not-exist.jte)");
+    }
 }