patch-shebangs: respect cross compilation

This hopefully makes patchShebangs respect cross compilation. It
introduces the concept of the HOST_PATH. Nothing is ever executed on
it but instead used as a way to get the proper path using ‘command
-v’. Needs more testing.

/cc @Ericson2314 @dtzWill

Fixes NixOS#33956
Fixes NixOS#21138

(Modified backport of f069423. See
previous commit to understand the differences between this and the
original.)

pkgs/build-support/setup-hooks/patch-shebangs.sh

@@ -5,10 +5,32 @@
 # rewritten to /nix/store/<hash>/bin/python.  Interpreters that are
 # already in the store are left untouched.
 
-fixupOutputHooks+=('if [ -z "$dontPatchShebangs" -a -e "$prefix" ]; then patchShebangs "$prefix"; fi')
+fixupOutputHooks+=(patchShebangsAuto)
+
+# Run patch shebangs on a directory.
+# patchShebangs [--build | --host] directory
+
+# Flags:
+# --build : Lookup commands available at build-time
+# --host  : Lookup commands available at runtime
+
+# Example use cases,
+# $ patchShebangs --host /nix/store/...-hello-1.0/bin
+# $ patchShebangs --build configure
 
 patchShebangs() {
+    local pathName
+
+    if [ "$1" = "--host" ]; then
+        pathName=HOST_PATH
+        shift
+    elif [ "$1" = "--build" ]; then
+        pathName=PATH
+        shift
+    fi
+
     local dir="$1"
+
     header "patching script interpreter paths in $dir"
     local f
     local oldPath
@@ -27,6 +49,14 @@ patchShebangs() {
         oldInterpreterLine=$(head -1 "$f" | tail -c+3)
         read -r oldPath arg0 args <<< "$oldInterpreterLine"
 
+        if [ -z "$pathName" ]; then
+            if [[ "$f" = "$NIX_STORE"* ]]; then
+                pathName=HOST_PATH
+            else
+                pathName=PATH
+            fi
+        fi
+
         if $(echo "$oldPath" | grep -q "/bin/env$"); then
             # Check for unsupported 'env' functionality:
             # - options: something starting with a '-'
@@ -35,14 +65,17 @@ patchShebangs() {
                 echo "unsupported interpreter directive \"$oldInterpreterLine\" (set dontPatchShebangs=1 and handle shebang patching yourself)"
                 exit 1
             fi
-            newPath="$(command -v "$arg0" || true)"
+
+            newPath="$(PATH="${!pathName}" command -v "$arg0" || true)"
         else
             if [ "$oldPath" = "" ]; then
                 # If no interpreter is specified linux will use /bin/sh. Set
                 # oldpath="/bin/sh" so that we get /nix/store/.../sh.
                 oldPath="/bin/sh"
             fi
-            newPath="$(command -v "$(basename "$oldPath")" || true)"
+
+            newPath="$(PATH="${!pathName}" command -v "$(basename "$oldPath")" || true)"
+
             args="$arg0 $args"
         fi
 
@@ -65,3 +98,17 @@ patchShebangs() {
 
     stopNest
 }
+
+patchShebangsAuto () {
+    if [ -z "$dontPatchShebangs" -a -e "$prefix" ]; then
+
+        # Dev output will end up being run on the build platform. An
+        # example case of this is sdl2-config. Otherwise, we can just
+        # use the runtime path (--host).
+        if [ "$output" != out ] && [ "$output" = "${!outputDev}" ]; then
+            patchShebangs --build "$prefix"
+        else
+            patchShebangs --host "$prefix"
+        fi
+    fi
+}