From 3f10635c2118b447453f431220a268929d6be393 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Fri, 4 Nov 2022 13:25:05 +0200
Subject: Detect in build.sh if installation directory is inside source

---
 build.sh.in | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/build.sh.in b/build.sh.in
index f9279b7..3dfb5be 100644
--- a/build.sh.in
+++ b/build.sh.in
@@ -461,19 +461,30 @@ if test -z "$idir"; then
   if test -z "$sudo"; then
     sudo="sudo"
   fi
-elif test -n "$(echo "$idir" | sed -n 's#^[^/].*$#true#p')"; then
+else
+  if test -n "$(echo "$idir" | sed -n 's#^[^/].*$#true#p')"; then
+    if ! command -v realpath >/dev/null 2>&1; then
+      diag "error: unable to execute realpath: command not found"
+      diag "  info: specify absolute installation directory path"
+      exit 1
+    fi
 
-  if ! command -v realpath >/dev/null 2>&1; then
-    diag "error: unable to execute realpath: command not found"
-    diag "  info: specify absolute installation directory path"
-    exit 1
+    # Don't resolve symlinks and allow non-existent path components.
+    #
+    if ! idir="$(realpath -s -m "$idir" 2>/dev/null)"; then
+      diag "error: realpath does not recognize -s -m"
+      diag "  info: specify absolute installation directory path"
+      exit 1
+    fi
   fi
 
-  # Don't resolve symlinks and allow non-existent path components.
+  # Check that it's not inside the build directory (we assume nobody
+  # is going to specify a path containing `#` or other special sed
+  # characters).
   #
-  if ! idir="$(realpath -s -m "$idir" 2>/dev/null)"; then
-    diag "error: realpath does not recognize -s -m"
-    diag "  info: specify absolute installation directory path"
+  eowd="$(echo "$owd" | sed 's%\([#.*^$\\[\]]\)%\\\1%g')"
+  if test -n "$(echo "$idir/" | sed -n "s#^$eowd/.*#true#p")"; then
+    diag "error: installation directory is inside current directory"
     exit 1
   fi
 fi
-- 
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