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text/template: fix slice builtin for pointers to arrays

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The slice function now properly handles pointers to arrays by calling
indirect() to dereference pointers, matching the behavior of the index
function.

Fixes #39596

Change-Id: Id4920edbfd8fd3df3a181b59a61733f88b0f104d
Reviewed-on: https://go-review.googlesource.com/c/go/+/727400
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
Nathan Nguyen 2025-12-05 15:50:24 -05:00 committed by Sean Liao
parent 6713f46426
commit b7944a5f80
2 changed files with 10 additions and 1 deletions
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7
src/text/template/exec_test.go
View File

@ -43,7 +43,8 @@ type T struct {
SIEmpty []int
SB []bool
// Arrays
AI [3]int
AI [3]int
PAI *[3]int // pointer to array
// Maps
MSI map[string]int
MSIone map[string]int // one element, for deterministic output
@ -142,6 +143,7 @@ var tVal = &T{
SI: []int{3, 4, 5},
SICap: make([]int, 5, 10),
AI: [3]int{3, 4, 5},
PAI: &[3]int{3, 4, 5},
SB: []bool{true, false},
MSI: map[string]int{"one": 1, "two": 2, "three": 3},
MSIone: map[string]int{"one": 1},
@ -556,6 +558,9 @@ var execTests = []execTest{
{"array[:]", "{{slice .AI}}", "[3 4 5]", tVal, true},
{"array[1:]", "{{slice .AI 1}}", "[4 5]", tVal, true},
{"array[1:2]", "{{slice .AI 1 2}}", "[4]", tVal, true},
{"pointer to array[:]", "{{slice .PAI}}", "[3 4 5]", tVal, true},
{"pointer to array[1:]", "{{slice .PAI 1}}", "[4 5]", tVal, true},
{"pointer to array[1:2]", "{{slice .PAI 1 2}}", "[4]", tVal, true},
{"string[:]", "{{slice .S}}", "xyz", tVal, true},
{"string[0:1]", "{{slice .S 0 1}}", "x", tVal, true},
{"string[1:]", "{{slice .S 1}}", "yz", tVal, true},

4
src/text/template/funcs.go
View File

@ -244,6 +244,10 @@ func slice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error)
if !item.IsValid() {
return reflect.Value{}, fmt.Errorf("slice of untyped nil")
}
var isNil bool
if item, isNil = indirect(item); isNil {
return reflect.Value{}, fmt.Errorf("slice of nil pointer")
}
if len(indexes) > 3 {
return reflect.Value{}, fmt.Errorf("too many slice indexes: %d", len(indexes))
}