tools/syz-linter: check variable declarations

Warn about:

var x int = foo

In most cases this can be expressed shorter as:

var x int
x := foo
x := int(foo)

Update #1876

2 files changed, 29 insertions, 0 deletions

diff --git a/tools/syz-linter/linter.go b/tools/syz-linter/linter.go
index 44fb91fbc..327e8b977 100644
--- a/tools/syz-linter/linter.go
+++ b/tools/syz-linter/linter.go
@@ -60,6 +60,8 @@ func run(pass *analysis.Pass) (interface{}, error) {
 				checkFuncArgs(pass, n)
 			case *ast.CallExpr:
 				checkLogErrorFormat(pass, n)
+			case *ast.GenDecl:
+				checkVarDecl(pass, n)
 			}
 			return true
 		})
@@ -216,3 +218,21 @@ func checkLogErrorFormat(pass *analysis.Pass, n *ast.CallExpr) {
 }
 
 var publicIdentifier = regexp.MustCompile(`^[A-Z][[:alnum:]]+(\.[[:alnum:]]+)+ `)
+
+// checkVarDecl warns about unnecessary long variable declarations "var x type = foo".
+func checkVarDecl(pass *analysis.Pass, n *ast.GenDecl) {
+	if n.Tok != token.VAR {
+		return
+	}
+	for _, s := range n.Specs {
+		spec, ok := s.(*ast.ValueSpec)
+		if !ok || spec.Type == nil || len(spec.Values) == 0 || spec.Names[0].Name == "_" {
+			continue
+		}
+		pass.Report(analysis.Diagnostic{
+			Pos: n.Pos(),
+			Message: "Don't use both var, type and value in variable declarations\n" +
+				"Use either \"var x type\" or \"x := val\" or \"x := type(val)\"",
+		})
+	}
+}
diff --git a/tools/syz-linter/testdata/src/lintertest/lintertest.go b/tools/syz-linter/testdata/src/lintertest/lintertest.go
index 7b8722693..9a8c965b8 100644
--- a/tools/syz-linter/testdata/src/lintertest/lintertest.go
+++ b/tools/syz-linter/testdata/src/lintertest/lintertest.go
@@ -66,3 +66,12 @@ func logErrorMessages() {
 	log.Print("no new lines\n") // want "Don't use \\\\n at the end of log/error messages"
 	log.Print("") // want "Don't use empty log/error messages"
 }
+
+func varDecls() {
+	var a int
+	b := 0
+	c := int64(0)
+	var _ int = 0
+	var d int = 0	// want "Don't use both var, type and value in variable declarations"
+	_, _, _, _ = a, b, c, d
+}