make: DESTDIR must be an absolute path

Clarify in the installation notes, and add a check in the makefile.

Closes PR 14935

INSTALL.txt

@@ -74,22 +74,24 @@ See "More Instructions: Building Racket" below for more information.
 Quick Instructions: Unix-style Install
 ======================================
 
-On Unix, `make unix-style PREFIX=<dir>' builds and installs into <dir>
-with binaries in "<dir>/bin", packages in "<dir>/share/racket/pkgs",
-documentation in "<dir>/share/racket/doc", etc.
+On Unix, `make unix-style PREFIX=<dir>' builds and installs into
+"<dir>" (which must be an absolute path) with binaries in "<dir>/bin",
+packages in "<dir>/share/racket/pkgs", documentation in
+"<dir>/share/racket/doc", etc.
 
 On Mac OS X, `make unix-style PREFIX=<dir>' builds and installs into
-"<dir>" with binaries in "<dir>/bin", packges in "<dir>/share/pkgs",
-documentation in "<dir>/doc", etc.
+"<dir>" (whichmust be an absolute path) with binaries in "<dir>/bin",
+packges in "<dir>/share/pkgs", documentation in "<dir>/doc", etc.
 
 On Windows, Unix-style install is not supported.
 
 A Unix-style install leaves no reference to this source directory.
 
 To split the build and install steps of a Unix-style installation,
 supply `DESTDIR=<dest-dir>' with `make unix-style PREFIX=<dir>', which
-assembles the installation in "<dest-dir>". Then, copy the content of
-"<dest-dir>" to the target root.
+assembles the installation in "<dest-dir>" (which must be an absolute
+path). Then, copy the content of "<dest-dir>" to the target root
+"<dir>".
 
 See "More Instructions: Building Racket" below for more information.
 

racket/src/Makefile.in

@@ -92,6 +92,11 @@ plain-install:
 	$(MAKE) plain-install-@MAIN_VARIANT@
 
 install-common-first:
+	if [ "$(DESTDIR)" != "" ]; then \
+          if [[ "$(DESTDIR)" != /* ]]; then \
+            echo "expected an absolute path for DESTDIR; given: $(DESTDIR)"; exit 1; \
+          fi; \
+        fi
 	mkdir -p $(ALLDIRINFO)
 
 install-common-middle:

racket/src/README

@@ -227,11 +227,12 @@ Detailed instructions:
     can find the installation directories.  At this stage, in case you
     are packaging an installation instead of installing directly, you
     can redirect the installation by setting the "DESTDIR" environment
-    variable.  For example, `make DESTDIR=/tmp/racket-build install'
-    places the installation into "/tmp/racket-build" instead of the
-    location originally specified with `--prefix'.  The resulting
-    installation will not work, however, until it is moved to the
-    location originally specified with `--prefix'.
+    variable to an absolute path for the packaging area. For example,
+    `make DESTDIR=/tmp/racket-build install' places the installation
+    into "/tmp/racket-build" instead of the location originally
+    specified with `--prefix'.  The resulting installation will not
+    work, however, until it is moved to the location originally
+    specified with `--prefix'.
 
     Finally, the `make install' step compiles ".zo" bytecode files for
     installed Racket source, generates launcher programs like