regexp: fix index panic in Replace
When using subexpressions ($1) as replacements, when they either don't exist or values weren't found causes a panic.
This patch ensures that the match location isn't -1, to prevent out of bounds errors.
Fixes #3816.
R=franciscossouza, rsc
CC=golang-dev
https://golang.org/cl/6931049
diff --git a/src/pkg/regexp/all_test.go b/src/pkg/regexp/all_test.go
index 3596573..9c4d64f 100644
--- a/src/pkg/regexp/all_test.go
+++ b/src/pkg/regexp/all_test.go
@@ -196,6 +196,10 @@
{"a+", "${oops", "aaa", "${oops"},
{"a+", "$$", "aaa", "$"},
{"a+", "$", "aaa", "$"},
+
+ // Substitution when subexpression isn't found
+ {"(x)?", "$1", "123", "123"},
+ {"abc", "$1", "123", "123"},
}
var replaceLiteralTests = []ReplaceTest{
