fix: better error reporting when ``shyaml`` fails not for syntax reasons.

bin/compose

@@ -2404,12 +2404,18 @@ debug "Found $WHITE$exname$NORMAL YAML file in '$COMPOSE_YML_FILE'."
 
 output=$(shyaml get-value < "$COMPOSE_YML_FILE" 2>&1)
 if [ "$?" != 0 ]; then
-    err "Invalid YAML in '$COMPOSE_YML_FILE':"
+    outputed_something=
     while IFS='' read -r line1 && IFS='' read -r line2; do
+        [ "$outputed_something" ] || err "Invalid YAML in '$COMPOSE_YML_FILE':"
+        outputed_something=true
         echo "$line1 $GRAY($line2)$NORMAL"
     done < <(echo "$output" | grep ^yaml.scanner -A 100 |
                     sed -r 's/^  in "<stdin>", //g' | sed -r 's/^yaml.scanner.[a-zA-Z]+: //g') |
         prefix "  $GRAY|$NORMAL "
+    [ "$outputed_something" ] || {
+        err "Unexpected error while running 'shyaml get-value' on '$COMPOSE_YML_FILE':"
+        echo "$output" | prefix "  $GRAY|$NORMAL "
+        }
     exit 1
 fi