Implementing nil as a literal in the Go language frontend (#897)

Fixes #447

cpg-language-go/src/main/golang/frontend/handler.go

@@ -1184,7 +1184,16 @@ func (this *GoLanguageFrontend) handleCompositeLit(fset *token.FileSet, lit *ast
 	return c
 }
 
-func (this *GoLanguageFrontend) handleIdent(fset *token.FileSet, ident *ast.Ident) *cpg.DeclaredReferenceExpression {
+func (this *GoLanguageFrontend) handleIdent(fset *token.FileSet, ident *ast.Ident) *cpg.Expression {
+	// Check, if this is 'nil', because then we handle it as a literal in the graph
+	if ident.Name == "nil" {
+		lit := cpg.NewLiteral(fset, ident)
+
+		(*cpg.Node)(lit).SetName(ident.Name)
+
+		return (*cpg.Expression)(lit)
+	}
+
 	ref := cpg.NewDeclaredReferenceExpression(fset, ident)
 
 	tu := this.GetCurrentTU()
@@ -1199,7 +1208,7 @@ func (this *GoLanguageFrontend) handleIdent(fset *token.FileSet, ident *ast.Iden
 
 	ref.SetName(ident.Name)
 
-	return ref
+	return (*cpg.Expression)(ref)
 }
 
 func (this *GoLanguageFrontend) handleTypeAssertExpr(fset *token.FileSet, assert *ast.TypeAssertExpr) *cpg.CastExpression {

cpg-language-go/src/test/kotlin/de/fraunhofer/aisec/cpg/frontends/golang/GoLanguageFrontendTest.kt

@@ -247,6 +247,15 @@ class GoLanguageFrontendTest : BaseTest() {
         assertNotNull(f32)
         assertEquals("f32", f32.name)
         assertEquals(TypeParser.createFrom("float32", false), f32.type)
+
+        val n = p.byNameOrNull<VariableDeclaration>("n")
+        assertNotNull(n)
+        assertEquals(TypeParser.createFrom("int*", false), n.type)
+
+        val nil = n.initializer as? Literal<*>
+        assertNotNull(nil)
+        assertEquals("nil", nil.name)
+        assertEquals(null, nil.value)
     }
 
     @Test

cpg-language-go/src/test/resources/golang/literal.go

@@ -4,3 +4,4 @@ const a = 1
 const s = "test"
 const f = 1.0
 const f32 float32 = 1.00
+var n *int = nil