Avoid ArgumentOutOfRangeException in ExpressionHelper.CheckForString (#1649)

src/Generator/Passes/ExpressionHelper.cs

@@ -427,8 +427,17 @@ namespace CppSharp.Internal
 
                 if (typeInSignature is CILType managed && managed.Type == typeof(string))
                 {
-                    result = result[result.IndexOf("\"")..];
-                    return true;
+                    // It is possible that "result" is not a string literal. See, for
+                    // example, the test case MoreVariablesWithInitializer in CSharp.h.
+                    // Test for presence of a quote first to avoid
+                    // ArgumentOutOfRangeException.
+                    var initialQuoteIndex = result.IndexOf("\"");
+                    if (initialQuoteIndex >= 0)
+                    { 
+                        result = result[initialQuoteIndex..];
+                        return true;
+                    }
+                    return false;
                 }
             }
             return false;

tests/CSharp/CSharp.Tests.cs

@@ -934,6 +934,15 @@ public unsafe class CSharpTests
         Assert.That(VariablesWithInitializer.BoolArray, Is.EqualTo(new[] { false, true }));
     }
 
+    [Test]
+    public void TestIndirectVariableInitializer()
+    {
+        // The actual test is that the generator doesn't throw when generating
+        // IndependentStringVariable. If we're running the test, we must have
+        // generated CSharp.cs without crashing the generator.
+        Assert.That(MoreVariablesWithInitializer.DependentStringVariable, Is.EqualTo(MoreVariablesWithInitializer.IndependentStringVariable));
+    }
+
     [Test]
     public void TestPointerPassedAsItsSecondaryBase()
     {

tests/CSharp/CSharp.h

@@ -1096,6 +1096,18 @@ public:
    static constexpr float FloatArray[2] { 0.5020f, 0.6020f };
 };
 
+// Try to precipitate an ArgumentOutOfRangeException in ExpressionHelper.CheckForString.
+//
+// Note that uncommenting DLL_API below results in different behavior in
+// ExpressionHelper.PrintExpression. In particular, ExpressionHelper.CheckForString is not
+// called and no ArgumentOutOfRangeException is generated.
+#define STRING_INITIALIZER "The quick brown fox"
+struct /*DLL_API*/ MoreVariablesWithInitializer
+{
+    static constexpr const char* IndependentStringVariable = STRING_INITIALIZER;
+    static constexpr const char* DependentStringVariable = IndependentStringVariable;
+};
+
 typedef void (*ALLCAPS_UNDERSCORES)(int i);
 
 class DLL_API TestString