From e3f3a5411a3f60d8ab52fb335ee4eff6eb531fd9 Mon Sep 17 00:00:00 2001 From: Gustavo Niemeyer Date: Mon, 15 Aug 2011 00:22:28 -0300 Subject: [PATCH] exp/template: don't panic on range of nil interface This avoids a non-obvious panic when range is used on a nil interface, and fixes it by behaving as if the range was empty. The new behavior is equivalent to the outcome of iterating on a nil map or slice, and is useful because it allows generic structures such as used in json (map[string]interface{}) to behave correctly if a key generally set to a list or map isn't present. R=golang-dev, r, gustavo CC=golang-dev https://golang.org/cl/4876046 --- src/pkg/exp/template/exec.go | 4 +++- src/pkg/exp/template/exec_test.go | 1 + 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/src/pkg/exp/template/exec.go b/src/pkg/exp/template/exec.go index ff4e3876af..06e5d2b3b8 100644 --- a/src/pkg/exp/template/exec.go +++ b/src/pkg/exp/template/exec.go @@ -233,8 +233,10 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) { s.pop(mark) } return + case reflect.Invalid: + break // An invalid value is likely a nil map, etc. and acts like an empty map. default: - s.errorf("range can't iterate over value of type %T", val.Interface()) + s.errorf("range can't iterate over %v", val) } if r.ElseList != nil { s.walk(dot, r.ElseList) diff --git a/src/pkg/exp/template/exec_test.go b/src/pkg/exp/template/exec_test.go index a8ef64d2e0..8a610da63b 100644 --- a/src/pkg/exp/template/exec_test.go +++ b/src/pkg/exp/template/exec_test.go @@ -372,6 +372,7 @@ var execTests = []execTest{ {"range map else", "{{range .MSI | .MSort}}-{{.}}-{{else}}EMPTY{{end}}", "-one--three--two-", tVal, true}, {"range empty map else", "{{range .MSIEmpty}}-{{.}}-{{else}}EMPTY{{end}}", "EMPTY", tVal, true}, {"range empty interface", "{{range .Empty3}}-{{.}}-{{else}}EMPTY{{end}}", "-7--8-", tVal, true}, + {"range empty nil", "{{range .Empty0}}-{{.}}-{{end}}", "", tVal, true}, {"range $x SI", "{{range $x := .SI}}<{{$x}}>{{end}}", "<3><4><5>", tVal, true}, {"range $x $y SI", "{{range $x, $y := .SI}}<{{$x}}={{$y}}>{{end}}", "<0=3><1=4><2=5>", tVal, true}, {"range $x MSIone", "{{range $x := .MSIone}}<{{$x}}>{{end}}", "<1>", tVal, true}, -- 2.50.0