[bug#50814] [PATCH 4/5] guix: Prepare the UI for continuable &warning exceptions.

[Attila Lendvai <attila@lendvai.name>]

* guix/store.scm (call-with-store): Use dynamic-wind so that continuable
exceptions are not broken by being re-raised as non-continuable.  This is
needed for a later commit that uses continuable exceptions from within
git-authenticate to signal warnings to the user.  The reason for this is that
this way tests can explicitly check that a warning was signalled in certain
situations.
* guix/ui.scm (call-with-error-handling): Handle &warning type exceptions by
printing them to the user, and then continuing at the place they were
signalled at.
* guix/diagnostics.scm (emit-formatted-warning): New exported
function.
---
 guix/diagnostics.scm |  4 ++++
 guix/store.scm       | 16 ++++++++++------
 guix/ui.scm          | 11 ++++++++++-
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/guix/diagnostics.scm b/guix/diagnostics.scm
index 6a792febd4..343213fb45 100644
--- a/guix/diagnostics.scm
+++ b/guix/diagnostics.scm
@@ -48,6 +48,7 @@
             formatted-message?
             formatted-message-string
             formatted-message-arguments
+            emit-formatted-warning
 
             &fix-hint
             fix-hint?
@@ -161,6 +162,9 @@ messages."
     (report-error args ...)
     (exit 1)))
 
+(define* (emit-formatted-warning fmt . args)
+  (emit-diagnostic fmt args #:prefix (G_ "warning: ") #:colors %warning-color))
+
 (define* (emit-diagnostic fmt args
                           #:key location (colors (color)) (prefix ""))
   "Report diagnostic message FMT with the given ARGS and the specified
diff --git a/guix/store.scm b/guix/store.scm
index 89a719bcfc..33d4039037 100644
--- a/guix/store.scm
+++ b/guix/store.scm
@@ -45,6 +45,8 @@
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
   #:use-module (srfi srfi-39)
+  #:use-module ((rnrs conditions)
+                #:select (warning?))
   #:use-module (ice-9 match)
   #:use-module (ice-9 vlist)
   #:use-module (ice-9 popen)
@@ -651,19 +653,21 @@ connection.  Use with care."
 
 (define (call-with-store proc)
   "Call PROC with an open store connection."
-  (let ((store (open-connection)))
+  (let ((store '()))
     (define (thunk)
       (parameterize ((current-store-protocol-version
                       (store-connection-version store)))
         (call-with-values (lambda () (proc store))
           (lambda results
-            (close-connection store)
             (apply values results)))))
 
-    (with-exception-handler (lambda (exception)
-                              (close-connection store)
-                              (raise-exception exception))
-      thunk)))
+    (dynamic-wind
+      (lambda ()
+        (set! store (open-connection)))
+      thunk
+      (lambda ()
+        (close-connection store)
+        (set! store '())))))
 
 (define-syntax-rule (with-store store exp ...)
   "Bind STORE to an open connection to the store and evaluate EXPs;
diff --git a/guix/ui.scm b/guix/ui.scm
index 1428c254b3..88940f99ef 100644
--- a/guix/ui.scm
+++ b/guix/ui.scm
@@ -69,6 +69,8 @@
   #:use-module (srfi srfi-31)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
+  #:use-module ((rnrs conditions)
+                #:select (warning?))
   #:autoload   (ice-9 ftw)  (scandir)
   #:use-module (ice-9 match)
   #:use-module (ice-9 format)
@@ -689,7 +691,14 @@ evaluating the tests and bodies of CLAUSES."
     (and (not (port-closed? port))
          (port-filename port)))
 
-  (guard* (c ((package-input-error? c)
+  (guard* (c ((warning? c)
+              (if (formatted-message? c)
+                  (apply emit-formatted-warning
+                         (formatted-message-string c)
+                         (formatted-message-arguments c))
+                  (emit-formatted-warning "~a" c))
+              '())
+             ((package-input-error? c)
               (let* ((package  (package-error-package c))
                      (input    (package-error-invalid-input c))
                      (location (package-location package))
-- 
2.33.0