Improve OpSpecConstantOp failure message (KhronosGroup#6731)

Fixes KhronosGroup#6730

* Add a path to suggest the correct opcode for the assembler

Author: alan-baker

source/text.cpp

@@ -794,6 +794,18 @@ spv_result_t spvTextEncodeOpcode(const spvtools::AssemblyGrammar& grammar,
         if (spvOperandIsOptional(type)) {
           break;
         } else {
+          if (opcodeName == "OpSpecConstantOp" &&
+              type == SPV_OPERAND_TYPE_SPEC_CONSTANT_OP_NUMBER) {
+            std::string operandValue;
+            error = context->getWord(&operandValue, &nextPosition);
+            spv::Op opcode;
+            if (!grammar.lookupSpecConstantOpcode(operandValue.c_str() + 2,
+                                                  &opcode)) {
+              return context->diagnostic()
+                     << "Invalid " << opcodeName << " opcode '" << operandValue
+                     << "'. Did you mean '" << operandValue.substr(2) << "'?";
+            }
+          }
           return context->diagnostic()
                  << "Expected operand for " << opcodeName
                  << " instruction, but found the next instruction instead.";

test/text_to_binary.constant_test.cpp

@@ -827,6 +827,23 @@ INSTANTIATE_TEST_SUITE_P(
         {CASE(CompositeExtract), {0, 99, 42, 16, 17, 12, 19}},
     }));
 
+using TextToBinaryOpSpecConstantOpNegative =
+    spvtest::TextToBinaryTestBase<::testing::Test>;
+
+TEST_F(TextToBinaryOpSpecConstantOpNegative, BadEnum) {
+  std::string input = "%1 = OpSpecConstantOp %1 Add %3 %4";
+  EXPECT_THAT(CompileFailure(input),
+              testing::HasSubstr("Invalid OpSpecConstantOp opcode 'Add'"));
+}
+
+TEST_F(TextToBinaryOpSpecConstantOpNegative, NearMiss) {
+  std::string input = "%1 = OpSpecConstantOp %1 OpIAdd %3 %4";
+  EXPECT_THAT(
+      CompileFailure(input),
+      testing::HasSubstr(
+          "Invalid OpSpecConstantOp opcode 'OpIAdd'. Did you mean 'IAdd'?"));
+}
+
 // TODO(dneto): OpConstantTrue
 // TODO(dneto): OpConstantFalse
 // TODO(dneto): OpConstantComposite