utils: Allow wrap-program to be called multiple times.

* guix/build/utils.scm (wrap-program): Multiple invocations of
  wrap-program for the same file create successive wrappers.  Adjust
  docstring.
* tests/build-utils.scm: Test new wrap-program behavior.
  (%store): New variable.

1 files changed, 32 insertions, 12 deletions

diff --git a/guix/build/utils.scm b/guix/build/utils.scm
index d169053c7b..7257b30dfd 100644
--- a/guix/build/utils.scm
+++ b/guix/build/utils.scm
@@ -687,8 +687,7 @@ known as `nuke-refs' in Nixpkgs."
                              result))))))
 
 (define* (wrap-program prog #:rest vars)
-  "Rename PROG to .PROG-real and make PROG a wrapper.  VARS should look like
-this:
+  "Make a wrapper for PROG.  VARS should look like this:
 
   '(VARIABLE DELIMITER POSITION LIST-OF-DIRECTORIES)
 
@@ -697,23 +696,44 @@ where DELIMITER is optional.  ':' will be used if DELIMITER is not given.
 For example, this command:
 
   (wrap-program \"foo\"
-                '(\"PATH\" \":\" = (\"/nix/.../bar/bin\"))
-                '(\"CERT_PATH\" suffix (\"/nix/.../baz/certs\"
+                '(\"PATH\" \":\" = (\"/gnu/.../bar/bin\"))
+                '(\"CERT_PATH\" suffix (\"/gnu/.../baz/certs\"
                                         \"/qux/certs\")))
 
 will copy 'foo' to '.foo-real' and create the file 'foo' with the following
 contents:
 
   #!location/of/bin/bash
-  export PATH=\"/nix/.../bar/bin\"
-  export CERT_PATH=\"$CERT_PATH${CERT_PATH:+:}/nix/.../baz/certs:/qux/certs\"
+  export PATH=\"/gnu/.../bar/bin\"
+  export CERT_PATH=\"$CERT_PATH${CERT_PATH:+:}/gnu/.../baz/certs:/qux/certs\"
   exec location/of/.foo-real
 
 This is useful for scripts that expect particular programs to be in $PATH, for
 programs that expect particular shared libraries to be in $LD_LIBRARY_PATH, or
-modules in $GUILE_LOAD_PATH, etc."
-  (let ((prog-real (string-append (dirname prog) "/." (basename prog) "-real"))
-        (prog-tmp  (string-append (dirname prog) "/." (basename prog) "-tmp")))
+modules in $GUILE_LOAD_PATH, etc.
+
+If PROG has previously been wrapped by wrap-program the wrapper will point to
+the previous wrapper."
+  (define (wrapper-file-name number)
+    (format #f "~a/.~a-wrap-~2'0d" (dirname prog) (basename prog) number))
+  (define (next-wrapper-number)
+    (let ((wrappers
+           (find-files (dirname prog)
+                       (string-append "\\." (basename prog) "-wrap-.*"))))
+      (if (null? wrappers)
+          0
+          (string->number (string-take-right (last wrappers) 2)))))
+  (define (wrapper-target number)
+    (if (zero? number)
+        (let ((prog-real (string-append (dirname prog) "/."
+                                        (basename prog) "-real")))
+          (copy-file prog prog-real)
+          prog-real)
+        (wrapper-file-name number)))
+  (let* ((number   (next-wrapper-number))
+         (target   (wrapper-target number))
+         (wrapper  (wrapper-file-name (1+ number)))
+         (prog-tmp (string-append target "-tmp")))
     (define (export-variable lst)
       ;; Return a string that exports an environment variable.
       (match lst
@@ -736,8 +756,6 @@ modules in $GUILE_LOAD_PATH, etc."
          (format #f "export ~a=\"$~a${~a:+:}~a\""
                  var var var (string-join rest ":")))))
 
-    (copy-file prog prog-real)
-
     (with-output-to-file prog-tmp
       (lambda ()
         (format #t
@@ -745,9 +763,11 @@ modules in $GUILE_LOAD_PATH, etc."
                 (which "bash")
                 (string-join (map export-variable vars)
                              "\n")
-                (canonicalize-path prog-real))))
+                (canonicalize-path target))))
 
     (chmod prog-tmp #o755)
+    (rename-file prog-tmp wrapper)
+    (symlink wrapper prog-tmp)
     (rename-file prog-tmp prog)))
 
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