[c#] support for <Using Include=XXX> in csproj files (#5240)

Author: xavierpinho

joern-cli/frontends/csharpsrc2cpg/src/main/scala/io/joern/csharpsrc2cpg/utils/ImplicitUsingsCollector.scala

@@ -76,21 +76,40 @@ object ImplicitUsingsCollector {
       .collect { case x if x.label == "ImplicitUsings" => x.text }
       .exists(x => x == "true" || x == "enable")
 
-    val exclusions = rootElem.child
+    val usingsFromProjectType = if (projectType.isDefined && implicitUsingsEnabled) {
+      projectTypeMapping.getOrElse(projectType.get, Nil)
+    } else {
+      Nil
+    }
+
+    // Once we gather the initial set of implicit usings (if any) based on the project type, we
+    // process ItemGroup.Using tags. The order in which we process these matters, e.g.
+    //    <Using Include="System"/>
+    //    <Using Remove="System"/>
+    // removes "System", whereas
+    //    <Using Remove="System"/>
+    //    <Using Include="System"/>
+    // adds "System".
+
+    rootElem.child
       .collect { case x if x.label == "ItemGroup" => x.child }
       .flatten
-      .collect {
-        case x if x.label == "Using" && x.attribute("Remove").isDefined =>
-          x.attribute("Remove").flatMap(_.headOption.map(_.text))
-      }
+      .collect { case x if x.label == "Using" => x }
       .flatten
+      .foldLeft(usingsFromProjectType.toSet) { case (acc, node) =>
+        if (node.attribute("Remove").isDefined) {
+          node.attribute("Remove").flatMap(_.headOption.map(_.text)) match
+            case None           => acc
+            case Some(toRemove) => acc.excl(toRemove)
+        } else if (node.attribute("Include").isDefined) {
+          node.attribute("Include").flatMap(_.headOption.map(_.text)) match
+            case None            => acc
+            case Some(toInclude) => acc + toInclude
+        } else {
+          acc
+        }
+      }
       .toList
-
-    if (projectType.isDefined && implicitUsingsEnabled) {
-      projectTypeMapping.getOrElse(projectType.get, Nil).diff(exclusions)
-    } else {
-      Nil
-    }
   }
 
 }

joern-cli/frontends/csharpsrc2cpg/src/test/scala/io/joern/csharpsrc2cpg/querying/ast/ImplicitUsingsTests.scala

@@ -147,6 +147,86 @@ class ImplicitUsingsTests extends CSharpCode2CpgFixture {
         )
       }
     }
+
+    "accompanied by a NET.Sdk csproj with ImplicitUsings disabled but including `System`" should {
+      val cpg = code("""
+          |Console.WriteLine("Foo");
+          |""".stripMargin)
+        .moreCode(
+          """
+            |<Project Sdk="Microsoft.NET.Sdk">
+            | <PropertyGroup>
+            |   <OutputType>Exe</OutputType>
+            |   <ImplicitUsings>false</ImplicitUsings>
+            | </PropertyGroup>
+            | <ItemGroup>
+            |   <Using Include="System" />
+            | </ItemGroup>
+            |</Project>
+            |""".stripMargin,
+          fileName = "App.csproj"
+        )
+
+      "resolve WriteLine call" in {
+        cpg.call.nameExact("WriteLine").methodFullName.l shouldBe List(
+          "System.Console.WriteLine:System.Void(System.String)"
+        )
+      }
+    }
+
+    "accompanied by a NET.Sdk csproj with ImplicitUsings enabled but including and excluding `System`" should {
+      val cpg = code("""
+          |Console.WriteLine("Foo");
+          |""".stripMargin)
+        .moreCode(
+          """
+            |<Project Sdk="Microsoft.NET.Sdk">
+            | <PropertyGroup>
+            |   <OutputType>Exe</OutputType>
+            |   <ImplicitUsings>true</ImplicitUsings>
+            | </PropertyGroup>
+            | <ItemGroup>
+            |   <Using Include="System" />
+            |   <Using Remove="System" />
+            | </ItemGroup>
+            |</Project>
+            |""".stripMargin,
+          fileName = "App.csproj"
+        )
+
+      "not resolve WriteLine call" in {
+        cpg.call.nameExact("WriteLine").methodFullName.l shouldBe List(
+          "<unresolvedNamespace>.WriteLine:<unresolvedSignature>"
+        )
+      }
+    }
+
+    "accompanied by a NET.Sdk csproj with ImplicitUsings enabled but excluding and including `System`" should {
+      val cpg = code("""
+          |Console.WriteLine("Foo");
+          |""".stripMargin)
+        .moreCode(
+          """
+            |<Project Sdk="Microsoft.NET.Sdk">
+            | <PropertyGroup>
+            |   <OutputType>Exe</OutputType>
+            |   <ImplicitUsings>true</ImplicitUsings>
+            | </PropertyGroup>
+            | <ItemGroup>
+            |   <Using Remove="System" />
+            |   <Using Include="System" />
+            | </ItemGroup>
+            |</Project>
+            |""".stripMargin,
+          fileName = "App.csproj"
+        )
+
+      "resolve WriteLine call" in {
+        cpg.call.nameExact("WriteLine").methodFullName.l shouldBe List(
+          "System.Console.WriteLine:System.Void(System.String)"
+        )
+      }
+    }
   }
 
 }