internal/symbols: compute db symbol name from ast.FuncDecl

This is part of a series of CLs implementing automatic symbol extraction.

Change-Id: I4028ef7d1938644684a06a0971a05a7acbbb93b2
Reviewed-on: https://go-review.googlesource.com/c/vulndb/+/535295
Run-TryBot: Zvonimir Pavlinovic <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Tatiana Bradley <[email protected]>

internal/symbols/patched_functions.go

@@ -6,10 +6,13 @@ package main
 
 import (
 	"errors"
+	"fmt"
+	"go/ast"
 	"io/fs"
 	"os"
 	"path"
 	"path/filepath"
+	"reflect"
 	"strings"
 
 	"golang.org/x/mod/modfile"
@@ -162,3 +165,32 @@ func packageImportPath(module, moduleRoot, pkgPath string) string {
 	rel = filepath.ToSlash(rel) // cross platform
 	return path.Join(module, rel)
 }
+
+// symbolName returns the name of f as a symbol in
+// a vulnerability database.
+func symbolName(f *ast.FuncDecl) string {
+	name := f.Name.Name
+	if f.Recv == nil || len(f.Recv.List) == 0 {
+		return name
+	}
+	field := f.Recv.List[0]
+	if len(field.Names) == 0 {
+		return "" // sanity
+	}
+
+	t := ""
+	switch xv := field.Type.(type) {
+	case *ast.StarExpr:
+		if si, ok := xv.X.(*ast.Ident); ok {
+			t = si.Name
+		}
+	case *ast.Ident:
+		t = xv.Name
+	case *ast.IndexExpr:
+		// TODO(#63535): cover index instructions stemming from generics
+		return ""
+	default:
+		panic(fmt.Sprintf("symbolName: unexpected receiver type: %v\n", reflect.TypeOf(field.Type)))
+	}
+	return t + "." + name
+}

internal/symbols/patched_functions_test.go

@@ -4,6 +4,9 @@
 package main
 
 import (
+	"go/ast"
+	"go/parser"
+	"go/token"
 	"path/filepath"
 	"sort"
 	"testing"
@@ -80,3 +83,34 @@ func TestPackageImportPath(t *testing.T) {
 		}
 	}
 }
+
+func TestSymbolName(t *testing.T) {
+	src := `
+package p
+
+func Foo() {}
+
+type A struct {}
+func (a A) Do() {}
+
+type B struct {}
+func (b *B) Do() {}
+`
+	fset := token.NewFileSet() // positions are relative to fset
+	f, err := parser.ParseFile(fset, "src.go", src, 0)
+	if err != nil {
+		t.Error(err)
+	}
+
+	var got []string
+	for _, decl := range f.Decls {
+		if fn, ok := decl.(*ast.FuncDecl); ok {
+			got = append(got, symbolName(fn))
+		}
+	}
+	sort.Strings(got)
+	want := []string{"A.Do", "B.Do", "Foo"}
+	if diff := cmp.Diff(want, got); diff != "" {
+		t.Errorf("(-got, want+):\n%s", diff)
+	}
+}