config/name_values: fix index out of range in looksLikeSentences

configs/named_values.go

@@ -399,7 +399,7 @@ func looksLikeSentences(s string) bool {
 	}
 	runes := []rune(s) // HCL guarantees that all strings are valid UTF-8
 	first := runes[0]
-	last := runes[len(s)-1]
+	last := runes[len(runes)-1]
 
 	// If the first rune is a letter then it must be an uppercase letter.
 	// (This will only see the first rune in a multi-rune combining sequence,

configs/named_values_test.go

@@ -0,0 +1,33 @@
+package configs
+
+import (
+	"testing"
+)
+
+func Test_looksLikeSentences(t *testing.T) {
+	tests := map[string]struct {
+		args string
+		want bool
+	}{
+		"empty sentence": {
+			args: "",
+			want: false,
+		},
+		"valid sentence": {
+			args: "A valid sentence.",
+			want: true,
+		},
+		"valid sentence with an accent": {
+			args: `A Valid sentence with an accent "é".`,
+			want: true,
+		},
+	}
+
+	for name, tt := range tests {
+		t.Run(name, func(t *testing.T) {
+			if got := looksLikeSentences(tt.args); got != tt.want {
+				t.Errorf("looksLikeSentences() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}