caddyfile: Fix `import` replacing unrelated placeholders (#4129)

* caddyfile: Fix `import` replacing unrelated placeholders

See https://caddy.community/t/snippet-issue-works-outside-snippet/12231

So it turns out that `NewReplacer()` gives a replacer with some global defaults (like `{env.*}` and some system and time placeholders), which is not ideal when running `import` because we just want to replace `{args.*}` only, and nothing else.

* caddyfile: Add test

1 files changed, 12 insertions, 0 deletions

diff --git a/replacer.go b/replacer.go
index 29d8e26a7..e6cfdede7 100644
--- a/replacer.go
+++ b/replacer.go
@@ -36,6 +36,18 @@ func NewReplacer() *Replacer {
 	return rep
 }
 
+// NewEmptyReplacer returns a new Replacer,
+// without the global default replacements.
+func NewEmptyReplacer() *Replacer {
+	rep := &Replacer{
+		static: make(map[string]interface{}),
+	}
+	rep.providers = []ReplacerFunc{
+		rep.fromStatic,
+	}
+	return rep
+}
+
 // Replacer can replace values in strings.
 // A default/empty Replacer is not valid;
 // use NewReplacer to make one.