function/stdlib: "Substr" returns zero length string when length is zero

zclconf · Mar 9, 2020 · 9ae7dd9 · 9ae7dd9
1 parent 440c597
commit 9ae7dd9
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diff --git a/cty/function/stdlib/string.go b/cty/function/stdlib/string.go
@@ -144,8 +144,14 @@ var SubstrFunc = function.New(&function.Spec{
 			}
 
 			offset += totalLen
+		} else if length == 0 {
+			// Short circuit here, after error checks, because if a
+			// string of length 0 has been requested it will always
+			// be the empty string
+			return cty.StringVal(""), nil
 		}
 
+
 		sub := in
 		pos := 0
 		var i int

diff --git a/cty/function/stdlib/string_test.go b/cty/function/stdlib/string_test.go
@@ -323,6 +323,12 @@ func TestSubstr(t *testing.T) {
 			cty.NumberIntVal(10),
 			cty.StringVal(""),
 		},
+		{
+			cty.StringVal("hello"),
+			cty.NumberIntVal(0),
+			cty.NumberIntVal(0),
+			cty.StringVal(""),
+		},
 		{
 			cty.StringVal("noël"),
 			cty.NumberIntVal(0),