Ensure installed stdlib artefacts have correct case (#10301)

* Ensure installed stdlib artefacts have correct case

* Abort install if stale artefacts found

Changes

@@ -133,11 +133,12 @@ Working version
   (Gabriel Scherer, review by Nicolás Ojeda Bär, Alain Frisch, Xavier Leroy,
    Daniel Bünzli and Stephen Dolan)
 
-* #10169, #10270: Use capitalized module names in the Standard Library prefixing
-  scheme to match Dune, e.g. Stdlib__String instead of Stdlib__string. This is a
-  breaking change only to code which attempted to use the internal names before.
-  The Standard Library generated by the Dune rules is now equivalent to the main
-  build (the Dune rules still do not generate a distributable compiler).
+* #10169, #10270, #10301: Use capitalized module names in the Standard Library
+  prefixing scheme to match Dune, e.g. Stdlib__String instead of Stdlib__string.
+  This is a breaking change only to code which attempted to use the internal
+  names before. The Standard Library generated by the Dune rules is now
+  equivalent to the main build (the Dune rules still do not generate a
+  distributable compiler).
   (David Allsopp and Mark Shinwell, review by Gabriel Scherer)
 
 ### Other libraries:

stdlib/Makefile

@@ -56,6 +56,16 @@ allopt: stdlib.cmxa std_exit.cmx
 opt.opt: allopt
 
 .PHONY: install
+# Ensure any pre-4.13 lowercased artefacts are removed on macOS and Windows
+install::
+	stale="$(filter-out $(notdir $(wildcard stdlib__*.cmi)), \
+         $(notdir $(wildcard $(INSTALL_LIBDIR)/stdlib__*.cmi)))"; \
+  if test -n "$$stale" ; then \
+    echo "$(INSTALL_LIBDIR) contains stale stdlib artefacts"; \
+    echo "Please rm $(INSTALL_LIBDIR)/stdlib__*.cm* and re-run make install"; \
+    exit 1; \
+  fi
+
 install::
 	$(INSTALL_DATA) \
 	  stdlib.cma std_exit.cmo *.cmi camlheader_ur \
@@ -81,7 +91,17 @@ endif
 installopt: installopt-default
 
 .PHONY: installopt-default
-installopt-default:
+# Ensure any pre-4.13 lowercased artefacts are removed on macOS and Windows
+installopt-default::
+	stale="$(filter-out $(notdir $(wildcard stdlib__*.cmx)), \
+         $(notdir $(wildcard $(INSTALL_LIBDIR)/stdlib__*.cmx)))"; \
+  if test -n "$$stale" ; then \
+    echo "$(INSTALL_LIBDIR) contains stale stdlib artefacts"; \
+    echo "Please rm $(INSTALL_LIBDIR)/stdlib__*.cmx and re-run make install"; \
+    exit 1; \
+  fi
+
+installopt-default::
 	$(INSTALL_DATA) \
 	  stdlib.cmxa stdlib.$(A) std_exit.$(O) *.cmx \
 	  "$(INSTALL_LIBDIR)"