guix: substitute: Report the last progress in the child process.

Fixes <https://bugs.gnu.org/28756>.

* guix/utils.scm (filtered-port): Close the 'input' port for the current
process, and close it upon exit in the child process.
* guix/scripts/substitute.scm (progress-substitution): Display "\n\n" after
the reporter has finished.

guix/scripts/substitute.scm

@@ -956,19 +956,22 @@ DESTINATION as a nar file.  Verify the substitute against ACL."
                                      #:abbreviation nar-uri-abbreviation)))
                      (progress-report-port reporter raw)))
                   ((input pids)
+                   ;; NOTE: This 'progress' port of current process will be
+                   ;; closed here, while the child process doing the
+                   ;; reporting will close it upon exit.
                    (decompressed-port (and=> (narinfo-compression narinfo)
                                              string->symbol)
                                       progress)))
       ;; Unpack the Nar at INPUT into DESTINATION.
       (restore-file input destination)
       (close-port input)
-      (close-port progress)
+
+      ;; Wait for the reporter to finish.
+      (every (compose zero? cdr waitpid) pids)
 
       ;; Skip a line after what 'progress-reporter/file' printed, and another
       ;; one to visually separate substitutions.
-      (display "\n\n" (current-error-port))
+      (display "\n\n" (current-error-port)))))
-
-      (every (compose zero? cdr waitpid) pids))))
 
 
 ;;;

guix/utils.scm

@@ -153,9 +153,11 @@ buffered data is lost."
                   (close-port in)
                   (dump-port input out))
                 (lambda ()
+                  (close-port input)
                   (false-if-exception (close out))
                   (primitive-_exit 0))))
              (child
+              (close-port input)
               (close-port out)
               (loop in (cons child pids)))))))))