[c#] support top-level method declarations (#5224)

Author: xavierpinho

joern-cli/frontends/csharpsrc2cpg/src/main/scala/io/joern/csharpsrc2cpg/astcreation/AstForDeclarationsCreator.scala

@@ -410,7 +410,10 @@ trait AstForDeclarationsCreator(implicit withSchemaValidation: ValidationMode) {
     Seq(methodAst(methodNode_, thisNode +: params, body, methodReturn, modifiers))
   }
 
-  protected def astForMethodDeclaration(methodDecl: DotNetNodeInfo): Seq[Ast] = {
+  protected def astForMethodDeclaration(
+    methodDecl: DotNetNodeInfo,
+    extraModifiers: List[NewModifier] = Nil
+  ): Seq[Ast] = {
     val name = nameFromNode(methodDecl)
     val params = methodDecl
       .json(ParserKeys.ParameterList)
@@ -440,7 +443,7 @@ trait AstForDeclarationsCreator(implicit withSchemaValidation: ValidationMode) {
       if (!jsonBody.isNull && parseLevel == AstParseLevel.FULL_AST) astForBlock(createDotNetNodeInfo(jsonBody))
       else Ast(blockNode(methodDecl)) // Creates an empty block
     scope.popScope()
-    val modifiers = astForModifiers(methodDecl).flatMap(_.nodes).collect { case x: NewModifier => x }
+    val modifiers = astForModifiers(methodDecl).flatMap(_.nodes).collect { case x: NewModifier => x } ++ extraModifiers
     val thisNode =
       if (!modifiers.exists(_.modifierType == ModifierTypes.STATIC)) astForThisParameter(methodDecl)
       else Ast()

joern-cli/frontends/csharpsrc2cpg/src/main/scala/io/joern/csharpsrc2cpg/astcreation/AstForStatementsCreator.scala

@@ -6,7 +6,8 @@ import io.joern.csharpsrc2cpg.parser.ParserKeys
 import io.joern.csharpsrc2cpg.parser.DotNetJsonAst.*
 import io.joern.x2cpg.Ast
 import io.joern.x2cpg.ValidationMode
-import io.shiftleft.codepropertygraph.generated.{ControlStructureTypes, DispatchTypes, Operators}
+import io.joern.x2cpg.utils.NodeBuilders.newModifierNode
+import io.shiftleft.codepropertygraph.generated.{ControlStructureTypes, DispatchTypes, ModifierTypes, Operators}
 import io.shiftleft.codepropertygraph.generated.nodes.{
   NewControlStructure,
   NewFieldIdentifier,
@@ -279,8 +280,14 @@ trait AstForStatementsCreator(implicit withSchemaValidation: ValidationMode) { t
 
   }
 
-  protected def astForGlobalStatement(globalStatement: DotNetNodeInfo): Seq[Ast] = {
-    astForNode(globalStatement.json(ParserKeys.Statement))
+  private def astForGlobalStatement(globalStatement: DotNetNodeInfo): Seq[Ast] = {
+    val stmtNodeInfo = createDotNetNodeInfo(globalStatement.json(ParserKeys.Statement))
+    stmtNodeInfo.node match
+      // Denotes a top-level method declaration. These shall be added to the fictitious "main" created
+      // by `astForTopLevelStatements`.
+      case LocalFunctionStatement =>
+        astForMethodDeclaration(stmtNodeInfo, extraModifiers = newModifierNode(ModifierTypes.STATIC) :: Nil)
+      case _ => astForNode(stmtNodeInfo)
   }
 
   private def astForJumpStatement(jumpStmt: DotNetNodeInfo): Seq[Ast] = {

joern-cli/frontends/csharpsrc2cpg/src/main/scala/io/joern/csharpsrc2cpg/parser/DotNetJsonAst.scala

@@ -226,6 +226,8 @@ object DotNetJsonAst {
 
   object ReturnStatement extends JumpStatement
 
+  object LocalFunctionStatement extends DeclarationExpr with BaseStmt
+
   object AwaitExpression extends BaseExpr
 
   object PropertyDeclaration extends DeclarationExpr

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

@@ -1,6 +1,7 @@
 package io.joern.csharpsrc2cpg.querying.ast
 
 import io.joern.csharpsrc2cpg.testfixtures.CSharpCode2CpgFixture
+import io.shiftleft.codepropertygraph.generated.ModifierTypes
 import io.shiftleft.semanticcpg.language.*
 
 class TopLevelStatementTests extends CSharpCode2CpgFixture {
@@ -60,4 +61,18 @@ class TopLevelStatementTests extends CSharpCode2CpgFixture {
     }
   }
 
+  "top-level method becomes an inner static local method to the fictitious main" in {
+    val cpg = code("""
+        |void Run() {}
+        |""".stripMargin)
+    inside(cpg.method.nameExact("Run").l) {
+      case run :: Nil =>
+        run.methodReturn.typeFullName shouldBe "void"
+        run.fullName shouldBe "Test0_cs_Program.<Main>$.Run:void()"
+        run.modifier.modifierType.toSet shouldBe Set(ModifierTypes.STATIC, ModifierTypes.INTERNAL)
+        run.parentBlock.method.l shouldBe cpg.method.fullNameExact("Test0_cs_Program.<Main>$").l
+      case xs =>
+        fail(s"Expected single METHOD named Run, but found $xs")
+    }
+  }
 }