Workaround for identifying header files in the CFamily analyzer

Normally, the CFamily analyzer deduces that the file being analyzed is a
header when there is no exact match for the file name in the given
compilation database.

This is a temporary workaround to communicate with the analyzer that
the current file is a header file. This helps the analyzer avoid
reporting some FPs.

See https://sonarsource.atlassian.net/browse/CPP-2743

src/Integration.Vsix.UnitTests/CFamily/VcxProject/FileConfigTests.cs

@@ -174,6 +174,7 @@ public void TryGet_HeaderFileOptions_ReturnsValidConfig()
             // Assert
             request.Should().NotBeNull();
             Assert.AreEqual("\"C:\\path\\cl.exe\" /Yu\"pch.h\" /FI\"pch.h\" /EHsc /RTCu \"c:\\dummy\\file.h\"", request.CDCommand);
+            Assert.AreEqual("non_existent_file", request.CDFile);
 
             // Arrange
             projectItemConfig.FileConfigProperties["CompileAs"] = "CompileAsC";
@@ -184,6 +185,7 @@ public void TryGet_HeaderFileOptions_ReturnsValidConfig()
 
             // Assert
             Assert.AreEqual("\"C:\\path\\cl.exe\" /FI\"FHeader.h\" /Yu\"pch.h\" /EHsc /RTCu /TC \"c:\\dummy\\file.h\"", request.CDCommand);
+            Assert.AreEqual("non_existent_file", request.CDFile);
 
             // Arrange
             projectItemConfig.FileConfigProperties["CompileAs"] = "CompileAsCpp";
@@ -193,6 +195,7 @@ public void TryGet_HeaderFileOptions_ReturnsValidConfig()
 
             // Assert
             Assert.AreEqual("\"C:\\path\\cl.exe\" /FI\"FHeader.h\" /Yu\"pch.h\" /EHsc /RTCu /TP \"c:\\dummy\\file.h\"", request.CDCommand);
+            Assert.AreEqual("non_existent_file", request.CDFile);
         }
 
         [TestMethod]

src/Integration.Vsix/CFamily/VcxProject/FileConfig.cs

@@ -46,7 +46,8 @@ public static FileConfig TryGet(ILogger logger, ProjectItem dteProjectItem, stri
                 return null;
             }
 
-            CmdBuilder cmdBuilder = new CmdBuilder(vcFile.ItemType == "ClInclude");
+            var isHeader = vcFile.ItemType == "ClInclude";
+            CmdBuilder cmdBuilder = new CmdBuilder(isHeader);
 
             var compilerPath = vcConfig.GetEvaluatedPropertyValue("ClCompilerPath");
             if (string.IsNullOrEmpty(compilerPath))
@@ -75,7 +76,9 @@ public static FileConfig TryGet(ILogger logger, ProjectItem dteProjectItem, stri
             {
                 CDDirectory = Path.GetDirectoryName(vcProject.ProjectFile),
                 CDCommand = cmdBuilder.GetFullCmd(),
-                CDFile = absoluteFilePath,
+                // A hack to communicate with the CFamily analyzer that this is a header file.
+                // A long-term solution should be investigated in CPP-5898.
+                CDFile = isHeader ? "non_existent_file" : absoluteFilePath,
                 EnvInclude = envINCLUDE,
             };
         }