Fix the problem with inner double quotes

appveyor.yml

@@ -21,6 +21,9 @@ install:
   # However, secure variables are not decoded during Pull Request builds which prevents someone from submitting PR with malicious build script displaying those variables. In more controlled environment through with a trusted team and private GitHub repositories there is an option on General tab of project settings to allow secure variables for PRs.
 environment:
   PATH: $(PATH);$(PROGRAMFILES)\dotnet\
+
+  # https://www.appveyor.com/docs/build-configuration/#secure-variables
+  # However, secure variables are not decoded during Pull Request builds which prevents someone from submitting PR with malicious build script displaying those variables. In more controlled environment through with a trusted team and private GitHub repositories there is an option on General tab of project settings to allow secure variables for PRs.
   COVERALLS_REPO_TOKEN:
     secure: tsTABRbCmdWFLT194XNIrpurerOfjN6cEoxt2RaSUfLmUIgra/+CwuqVkv0sPRop
   SONAR_TOKEN:
@@ -62,6 +65,7 @@ test_script:
 - cmd: '"OpenCover\tools\OpenCover.Console.exe" -target:dotnet.exe -targetargs:"test test\System.Linq.Dynamic.Core.Tests\System.Linq.Dynamic.Core.Tests.csproj --configuration %CONFIGURATION% --framework netcoreapp1.1 --no-build" -output:coverage.xml -register:user -filter:"+[Microsoft.EntityFrameworkCore.DynamicLinq]* +[System.Linq.Dynamic.Core]* -[*Tests*]*" -nodefaultfilters -returntargetcode -oldstyle'
 - codecov -f "coverage.xml"
 - coveralls.net\tools\csmacnz.Coveralls.exe --opencover -i .\coverage.xml
+
 - ps: 'if (-Not $env:APPVEYOR_PULL_REQUEST_NUMBER) { & dotnet sonarscanner end /d:sonar.login="$env:SONAR_TOKEN" }'
 
 # Run tests for EntityFramework.DynamicLinq

src/System.Linq.Dynamic.Core/Parser/ExpressionParser.cs

@@ -755,6 +755,21 @@ Expression ParseStringLiteral()
             _textParser.ValidateToken(TokenId.StringLiteral);
             char quote = _textParser.CurrentToken.Text[0];
             string s = _textParser.CurrentToken.Text.Substring(1, _textParser.CurrentToken.Text.Length - 2);
+            int index1 = 0;
+            while (true)
+            {
+                int index2 = s.IndexOf(quote, index1);
+                if (index2 < 0)
+                {
+                    break;
+                }
+
+                if (index2 + 1 < s.Length && s[index2 + 1] == quote)
+                {
+                    s = s.Remove(index2, 1);
+                }
+                index1 = index2 + 1;
+            }
 
             if (quote == '\'')
             {

test/System.Linq.Dynamic.Core.Tests/DynamicExpressionParserTests.cs

@@ -440,5 +440,17 @@ public void ParseLambda_CustomMethod()
             // Assert
             Check.That(result).IsEqualTo(10);
         }
+
+        [Fact]
+        public void ParseLambda_With_InnerStringLiteral()
+        {
+            var originalTrueValue = "simple + \"quoted\"";
+            var doubleQuotedTrueValue = "simple + \"\"quoted\"\"";
+            var expressionText = $"iif(1>0, \"{doubleQuotedTrueValue}\", \"false\")";
+            var lambda = DynamicExpressionParser.ParseLambda(typeof(string), null, expressionText);
+            var del = lambda.Compile();
+            object result = del.DynamicInvoke(String.Empty);
+            Check.That(result).IsEqualTo(originalTrueValue);
+        }
     }
 }