[C++] check for not wrapped state in decodeLength()

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/cpp/CppGenerator.java

@@ -536,6 +536,18 @@ private static void generateAccessOrderException(
             .append(fieldPrecedenceModel.generatedRepresentationClassName()).append(".\");\n");
     }
 
+    private static void generateAccessOrderException(
+        final StringBuilder sb,
+        final String indent,
+        final String action)
+    {
+        sb.append(indent).append("throw AccessOrderError(")
+            .append("std::string(\"Illegal access. \") + \n")
+            .append(indent).append(INDENT)
+            .append("\"Cannot call \\\"").append(action)
+            .append("()\\\" in state: \" + codecStateName(codecState()));\n");
+    }
+
     private static void generateAccessOrderListenerMethodForNextGroupElement(
         final StringBuilder sb,
         final FieldPrecedenceModel fieldPrecedenceModel,
@@ -3027,6 +3039,7 @@ private CharSequence generateMessageFlyweightCode(
 
             "    SBE_NODISCARD std::uint64_t decodeLength() const\n" +
             "    {\n" +
+            "%22$s" +
             "        %10$s skipper(m_buffer, m_offset, m_bufferLength, m_actingBlockLength, m_actingVersion);\n" +
             "        skipper.skip();\n" +
             "        return skipper.encodedLength();\n" +
@@ -3071,7 +3084,8 @@ private CharSequence generateMessageFlyweightCode(
             generateCodecStateTransitionForWrappingLatestVersion(fieldPrecedenceModel),
             generateOnWrappedListener(fieldPrecedenceModel),
             generateCodecStateTransitionForWrapping(fieldPrecedenceModel),
-            generateHiddenCopyConstructor("    ", className));
+            generateHiddenCopyConstructor("    ", className),
+            generateCheckForNotWrappedState("decodeLength", fieldPrecedenceModel));
     }
 
     private CharSequence generateAccessOrderErrorType(final FieldPrecedenceModel fieldPrecedenceModel)
@@ -3311,6 +3325,31 @@ private CharSequence generateCodecStateTransitionForWrapping(final FieldPreceden
         return generateAccessOrderListenerCall(fieldPrecedenceModel, TWO_INDENT, "onWrapped", "actingVersion");
     }
 
+    private CharSequence generateCheckForNotWrappedState(
+        final String action,
+        final FieldPrecedenceModel fieldPrecedenceModel)
+    {
+        if (null == fieldPrecedenceModel)
+        {
+            return "";
+        }
+
+        final StringBuilder sb = new StringBuilder();
+        sb.append("#if defined(").append(precedenceChecksFlagName).append(")\n")
+            .append(TWO_INDENT)
+                .append("if (codecState() == ")
+                .append(qualifiedStateCase(fieldPrecedenceModel.notWrappedState()))
+                .append(")\n")
+            .append(TWO_INDENT).append("{\n");
+
+        generateAccessOrderException(sb, THREE_INDENT, action);
+
+        sb.append(TWO_INDENT).append("}\n")
+            .append("#endif\n");
+
+        return sb;
+    }
+
     private CharSequence generateCodecStateTransitionForWrappingLatestVersion(
         final FieldPrecedenceModel fieldPrecedenceModel
     )

sbe-tool/src/test/cpp/FieldAccessOrderCheckTest.cpp

@@ -5048,3 +5048,43 @@ TEST_F(FieldAccessOrderCheckTest, worksWithInsertionOperator)
     EXPECT_EQ(decoder.getBAsString(), "abc");
     EXPECT_EQ(decoder.getCAsString(), "def");
 }
+
+TEST_F(FieldAccessOrderCheckTest, shouldThrowExceptionWhenNotWrapped)
+{
+    MultipleVarLength encoder;
+    encoder.wrapForEncode(m_buffer, OFFSET, BUFFER_LEN);
+    encoder.a(42);
+    encoder.putB("abc");
+    encoder.putC("def");
+    encoder.checkEncodingIsComplete();
+
+    MultipleVarLength decoder;
+
+    EXPECT_THROW(
+        {
+            try
+            {
+                decoder.decodeLength();
+            }
+            catch (const std::exception &e)
+            {
+                EXPECT_THAT(
+                    e.what(),
+                    HasSubstr("Illegal access. Cannot call \"decodeLength()\" in state: NOT_WRAPPED")
+                );
+                throw;
+            }
+        },
+        std::logic_error
+    );
+
+    decoder.wrapForDecode(
+        m_buffer,
+        OFFSET,
+        MultipleVarLength::sbeBlockLength(),
+        MultipleVarLength::sbeSchemaVersion(),
+        BUFFER_LEN
+    );
+
+    decoder.decodeLength();
+}