test(pkg): PATH persists after initial env changed

test/blackbox-tests/test-cases/pkg/path-stability.t

@@ -0,0 +1,73 @@
+Test that package builds do not rebuild when PATH changes after initial build.
+This ensures builds are properly cached based on package content, not environment.
+
+  $ . ./helpers.sh
+
+Create a program that will be used during the build:
+
+  $ mkdir tool_v1
+  $ cat > tool_v1/mytool <<EOF
+  > #!/usr/bin/env sh
+  > echo "version1"
+  > EOF
+  $ chmod +x tool_v1/mytool
+
+Set up initial PATH and create a simple package:
+
+  $ export PATH="$PWD/tool_v1:$PATH"
+
+  $ make_lockdir
+  $ make_lockpkg foo <<EOF
+  > (version 0.0.1)
+  > (build
+  >  (progn
+  >   (system "mytool > output.txt")
+  >   (system "cat output.txt")))
+  > (install
+  >  (system "mkdir -p %{lib}/foo && cp output.txt %{lib}/foo/"))
+  > EOF
+
+Build the package for the first time:
+
+  $ build_pkg foo
+  version1
+
+Verify the installed file has the correct content:
+
+  $ prefix=$(get_build_pkg_dir foo)
+  $ cat "$prefix/target/lib/foo/output.txt"
+  version1
+
+Now create a different version of the tool:
+
+  $ mkdir tool_v2
+  $ cat > tool_v2/mytool <<EOF
+  > #!/usr/bin/env sh
+  > echo "version2"
+  > EOF
+  $ chmod +x tool_v2/mytool
+
+Change PATH to use the new tool:
+
+  $ export PATH="$PWD/tool_v2:$PATH"
+
+Verify the new tool is now in PATH:
+
+  $ which mytool
+  $TESTCASE_ROOT/tool_v2/mytool
+  $ mytool
+  version2
+
+Rebuild the package - it should use the cached build and NOT rebuild,
+so the output should still be version1:
+
+  $ build_pkg foo
+
+The installed file should still have the original version (not rebuilt):
+
+  $ cat "$prefix/target/lib/foo/output.txt"
+  version1
+
+  $ dune clean
+  $ build_pkg foo
+  version2