Merge bitcoin/bitcoin#33073: guix: warn SOURCE_DATE_EPOCH set in guix-codesign

1bed0f7 guix: warn SOURCE_DATE_EPOCH set in guix-codesign (will)

Pull request description:

  #32678 added a sanity check for this environment variable when running `guix-build` but missed that `guix-codesign` also relies on `SOURCE_DATE_EPOCH`, which can result in non-determinism in the codesigning step: bitcoin-core/guix.sigs#1720 (comment)

  To avoid repeating the logic move common functionality into the prelude and call the function in both guix actions.

ACKs for top commit:
  fanquake:
    ACK 1bed0f7

Tree-SHA512: ad3de8ab06e7f4ffcee5c02e8185b20879d63a02a614a706ea54da5087cca4ba75817ca1aa95301572c34723317fcc44e4478261ac73dd223ee9fa827e6b35b3

Author: fanquake

contrib/guix/guix-build

@@ -73,19 +73,7 @@ mkdir -p "$VERSION_BASE"
 # SOURCE_DATE_EPOCH should not unintentionally be set
 ################
 
-if [ -n "$SOURCE_DATE_EPOCH" ] && [ -z "$FORCE_SOURCE_DATE_EPOCH" ]; then
-cat << EOF
-ERR: Environment variable SOURCE_DATE_EPOCH is set which may break reproducibility.
-
-     Aborting...
-
-Hint: You may want to:
-      1. Unset this variable: \`unset SOURCE_DATE_EPOCH\` before rebuilding
-      2. Set the 'FORCE_SOURCE_DATE_EPOCH' environment variable if you insist on
-         using your own epoch
-EOF
-exit 1
-fi
+check_source_date_epoch
 
 ################
 # Build directories should not exist

contrib/guix/guix-codesign

@@ -67,6 +67,12 @@ EOF
 exit 1
 fi
 
+################
+# SOURCE_DATE_EPOCH should not unintentionally be set
+################
+
+check_source_date_epoch
+
 ################
 # The codesignature git worktree should not be dirty
 ################

contrib/guix/libexec/prelude.bash

@@ -21,6 +21,26 @@ check_tools() {
     done
 }
 
+################
+# SOURCE_DATE_EPOCH should not unintentionally be set
+################
+
+check_source_date_epoch() {
+    if [ -n "$SOURCE_DATE_EPOCH" ] && [ -z "$FORCE_SOURCE_DATE_EPOCH" ]; then
+        cat << EOF
+ERR: Environment variable SOURCE_DATE_EPOCH is set which may break reproducibility.
+
+     Aborting...
+
+Hint: You may want to:
+      1. Unset this variable: \`unset SOURCE_DATE_EPOCH\` before rebuilding
+      2. Set the 'FORCE_SOURCE_DATE_EPOCH' environment variable if you insist on
+         using your own epoch
+EOF
+        exit 1
+    fi
+}
+
 check_tools cat env readlink dirname basename git
 
 ################