From bf94da4667789c94296c32cb038e5238d314157b Mon Sep 17 00:00:00 2001
From: Ivan Ivanov <ivan.ivanov@ft.com>
Date: Sun, 1 May 2022 20:07:12 +0300
Subject: [PATCH] Fix gocognit output when a function has generic receiver type

recvString func in gocognit returns BADRECV when the function's receiver is a
generic type.

Implement recvString in two variants in order to keep the code
compatible with go versions less than 1.18
---
 gocognit.go    | 12 ------------
 recv.go        | 30 ++++++++++++++++++++++++++++++
 recv_pre118.go | 20 ++++++++++++++++++++
 3 files changed, 50 insertions(+), 12 deletions(-)
 create mode 100644 recv.go
 create mode 100644 recv_pre118.go

diff --git a/gocognit.go b/gocognit.go
index 418c163..1d539ee 100644
--- a/gocognit.go
+++ b/gocognit.go
@@ -49,18 +49,6 @@ func funcName(fn *ast.FuncDecl) string {
 	return fn.Name.Name
 }
 
-// recvString returns a string representation of recv of the
-// form "T", "*T", or "BADRECV" (if not a proper receiver type).
-func recvString(recv ast.Expr) string {
-	switch t := recv.(type) {
-	case *ast.Ident:
-		return t.Name
-	case *ast.StarExpr:
-		return "*" + recvString(t.X)
-	}
-	return "BADRECV"
-}
-
 // Complexity calculates the cognitive complexity of a function.
 func Complexity(fn *ast.FuncDecl) int {
 	v := complexityVisitor{
diff --git a/recv.go b/recv.go
new file mode 100644
index 0000000..b2e8b6a
--- /dev/null
+++ b/recv.go
@@ -0,0 +1,30 @@
+//go:build go1.18
+// +build go1.18
+
+package gocognit
+
+import (
+	"go/ast"
+	"strings"
+)
+
+// recvString returns a string representation of recv of the
+// form "T", "*T", Type[T], Type[T, V], or "BADRECV" (if not a proper receiver type).
+func recvString(recv ast.Expr) string {
+	switch t := recv.(type) {
+	case *ast.Ident:
+		return t.Name
+	case *ast.StarExpr:
+		return "*" + recvString(t.X)
+	case *ast.IndexExpr:
+		return recvString(t.X) + "[" + recvString(t.Index) + "]"
+	case *ast.IndexListExpr:
+		targs := make([]string, len(t.Indices))
+		for i, exp := range t.Indices {
+			targs[i] = recvString(exp)
+		}
+
+		return recvString(t.X) + "[" + strings.Join(targs, ", ") + "]"
+	}
+	return "BADRECV"
+}
diff --git a/recv_pre118.go b/recv_pre118.go
new file mode 100644
index 0000000..9e0ebfd
--- /dev/null
+++ b/recv_pre118.go
@@ -0,0 +1,20 @@
+//go:build !go1.18
+// +build !go1.18
+
+package gocognit
+
+import (
+	"go/ast"
+)
+
+// recvString returns a string representation of recv of the
+// form "T", "*T", or "BADRECV" (if not a proper receiver type).
+func recvString(recv ast.Expr) string {
+	switch t := recv.(type) {
+	case *ast.Ident:
+		return t.Name
+	case *ast.StarExpr:
+		return "*" + recvString(t.X)
+	}
+	return "BADRECV"
+}