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, 31 insertions, 0 deletions

diff --git a/caddytest/integration/caddyfile_adapt/import_args_snippet_env_placeholder.txt b/caddytest/integration/caddyfile_adapt/import_args_snippet_env_placeholder.txt
new file mode 100644
index 0000000..1bc907e
--- /dev/null
+++ b/caddytest/integration/caddyfile_adapt/import_args_snippet_env_placeholder.txt
@@ -0,0 +1,31 @@
+(foo) {
+	respond {env.FOO}
+}
+
+:80 {
+	import foo
+}
+----------
+{
+	"apps": {
+		"http": {
+			"servers": {
+				"srv0": {
+					"listen": [
+						":80"
+					],
+					"routes": [
+						{
+							"handle": [
+								{
+									"body": "{env.FOO}",
+									"handler": "static_response"
+								}
+							]
+						}
+					]
+				}
+			}
+		}
+	}
+}
\ No newline at end of file