refactor: moves code related to AST from rule.utils into astutils package (#1380)

Modifications summary:

* Moves AST-related functions from rule/utils.go to astutils/ast_utils.go (+ modifies function calls)
* Renames some of these AST-related functions
* Avoids instantiating a printer config at each call to astutils.GoFmt
* Uses astutils.IsIdent and astutils.IsPkgDotName when possible

internal/astutils/ast_utils.go

@@ -2,8 +2,12 @@
 package astutils
 
 import (
+	"bytes"
+	"fmt"
 	"go/ast"
+	"go/printer"
 	"go/token"
+	"regexp"
 	"slices"
 )
 
@@ -78,9 +82,80 @@ func getFieldTypeName(typ ast.Expr) string {
 	}
 }
 
-// IsStringLiteral returns true if the given expression is a string literal, false otherwise
+// IsStringLiteral returns true if the given expression is a string literal, false otherwise.
 func IsStringLiteral(e ast.Expr) bool {
 	sl, ok := e.(*ast.BasicLit)
 
 	return ok && sl.Kind == token.STRING
 }
+
+// IsCgoExported returns true if the given function declaration is exported as Cgo function, false otherwise.
+func IsCgoExported(f *ast.FuncDecl) bool {
+	if f.Recv != nil || f.Doc == nil {
+		return false
+	}
+
+	cgoExport := regexp.MustCompile(fmt.Sprintf("(?m)^//export %s$", regexp.QuoteMeta(f.Name.Name)))
+	for _, c := range f.Doc.List {
+		if cgoExport.MatchString(c.Text) {
+			return true
+		}
+	}
+	return false
+}
+
+// IsIdent returns true if the given expression is the identifier with name ident, false otherwise.
+func IsIdent(expr ast.Expr, ident string) bool {
+	id, ok := expr.(*ast.Ident)
+	return ok && id.Name == ident
+}
+
+// IsPkgDotName returns true if the given expression is a selector expression of the form <pkg>.<name>, false otherwise.
+func IsPkgDotName(expr ast.Expr, pkg, name string) bool {
+	sel, ok := expr.(*ast.SelectorExpr)
+	return ok && IsIdent(sel.X, pkg) && IsIdent(sel.Sel, name)
+}
+
+// PickNodes yields a list of nodes by picking them from a sub-ast with root node n.
+// Nodes are selected by applying the selector function
+func PickNodes(n ast.Node, selector func(n ast.Node) bool) []ast.Node {
+	var result []ast.Node
+
+	if n == nil {
+		return result
+	}
+
+	onSelect := func(n ast.Node) {
+		result = append(result, n)
+	}
+	p := picker{selector: selector, onSelect: onSelect}
+	ast.Walk(p, n)
+	return result
+}
+
+type picker struct {
+	selector func(n ast.Node) bool
+	onSelect func(n ast.Node)
+}
+
+func (p picker) Visit(node ast.Node) ast.Visitor {
+	if p.selector == nil {
+		return nil
+	}
+
+	if p.selector(node) {
+		p.onSelect(node)
+	}
+
+	return p
+}
+
+var gofmtConfig = &printer.Config{Tabwidth: 8}
+
+// GoFmt returns a string representation of an AST subtree.
+func GoFmt(x any) string {
+	buf := bytes.Buffer{}
+	fs := token.NewFileSet()
+	gofmtConfig.Fprint(&buf, fs, x)
+	return buf.String()
+}