feature: add debug functionality and false positive test

analyzer.go

@@ -60,6 +60,8 @@ func (a *analyzer) run(pass *analysis.Pass) (interface{}, error) {
 	imports := checker.LoadImports(pass.Fset, ins)
 	issues := []*analysis.Diagnostic{}
 
+	debugFn := debugNoOp
+
 	// --- Preorder Checker ------------------------------------------------------
 	ins.Preorder([]ast.Node{(*ast.CallExpr)(nil)}, func(n ast.Node) {
 		callExpr := n.(*ast.CallExpr)
@@ -70,11 +72,15 @@ func (a *analyzer) run(pass *analysis.Pass) (interface{}, error) {
 			return
 		}
 
+		if a.withDebug {
+			debugFn = debug(pass.Fset)
+		}
+
 		fileImports := imports.LookupImports(fileName)
 
 		// Run checkers against call expression.
 		for _, check := range a.checkers {
-			violation := check.With(pass.TypesInfo, fileImports).Check(callExpr)
+			violation := check.With(pass.TypesInfo, fileImports, debugFn).Check(callExpr)
 			if violation != nil {
 				issues = append(issues, violation.Diagnostic(n.Pos(), n.End()))
 			}

debug.go

@@ -0,0 +1,22 @@
+package mirror
+
+import (
+	"fmt"
+	"go/ast"
+	"go/printer"
+	"go/token"
+	"os"
+	"strings"
+)
+
+// --- debug -------------------------------------------------------------------
+
+func debug(f *token.FileSet) func(ast.Expr, string, ...any) {
+	return func(node ast.Expr, format string, a ...any) {
+		printer.Fprint(os.Stderr, f, node)
+		fmt.Fprintln(os.Stderr, "\n"+strings.Repeat("^", 80))
+		fmt.Fprintf(os.Stderr, format, a...)
+	}
+}
+
+func debugNoOp(_ ast.Expr, _ string, _ ...any) {}

internal/checker/checker.go

@@ -13,6 +13,7 @@ type Checker struct {
 
 	types   *types.Info // used for checking types
 	imports []Import    // imports (of current file)
+	debug   func(ast.Expr, string, ...any)
 }
 
 // New will accept a name for package (like `text/template` or `strings`) and
@@ -151,8 +152,9 @@ func cleanName(name string) string {
 	return name
 }
 
-func (c *Checker) With(types *types.Info, i []Import) *Checker {
+func (c *Checker) With(types *types.Info, i []Import, debugFn func(ast.Expr, string, ...any)) *Checker {
 	c.types = types
 	c.imports = i
+	c.debug = debugFn
 	return c
 }

testdata/false_positive1.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/hex"
+	"log"
+)
+
+// using function that accepts string and process it and then return []bytes
+func S1() {
+	h := sha256.New()
+	if _, err := h.Write([]byte("foobar")); err != nil {
+		log.Fatal(err)
+	}
+
+	contentBuf := bytes.NewBufferString("foo-bar\n")
+	contentBuf.WriteString(hex.EncodeToString(h.Sum(nil))) // false postitve
+}