From bd0776f89ebf49254c20951113f9b3b84d37514e Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sun, 15 May 2022 15:09:29 +0100
Subject: [PATCH] subst: Have substitutor handle any needle syntax

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 src/shapelib.rs | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/shapelib.rs b/src/shapelib.rs
index d0aa4e99..92a606db 100644
--- a/src/shapelib.rs
+++ b/src/shapelib.rs
@@ -1129,13 +1129,20 @@ impl<'i> Substituting<'i> {
       },
       Dollars::Text => { },
     }
-    let needle: Cow<str> = if self.do_dollars() {
-      let token = needle.strip_prefix('_')
-        .ok_or_else(|| self.internal_err("needle has no '_'"))?;
-      format!("${{{}}}", token).into()
-    } else {
-      needle
-    };
+    let needle: Cow<str> = (move || Some({
+      if let Some(rhs) = needle.strip_prefix("${") {
+        let token = rhs.strip_suffix("}")?;
+        if self.do_dollars() { needle.into() }
+        else { format!("_{}", token).into() }
+      } else if let Some(token) = needle.strip_prefix("_") {
+        if ! self.do_dollars() { needle.into() }
+        else { format!("${{{}}}", token).into() }
+      } else {
+        return None
+      }
+    }))()
+      .ok_or_else(|| self.internal_err("needle has no '_'"))?;
+
     let (r, count) = self.subst_general_precisely(&needle, replacement)?;
     (r, count, needle)
   }
-- 
2.30.2