From b5c4382bef8c688d0cf63f554a7d886faddc77cb Mon Sep 17 00:00:00 2001
From: Gilles Peskine <Gilles.Peskine@arm.com>
Date: Tue, 5 Apr 2022 14:08:09 +0200
Subject: [PATCH] check-generated-files.sh -u: don't update file timestamps

When running check-generated-files in update mode, all generated files were
regenerated. As a consequence,
```
tests/scripts/check-generated-files.sh -u && make
```
always caused most of the code to be rebuilt. Now, if a file hasn't changed,
preserve its original modification time (and other metadata), so the command
above doesn't rebuild anything that has actually not changed.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
---
 tests/scripts/check-generated-files.sh | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/tests/scripts/check-generated-files.sh b/tests/scripts/check-generated-files.sh
index 5e35be8f9..75730ba25 100755
--- a/tests/scripts/check-generated-files.sh
+++ b/tests/scripts/check-generated-files.sh
@@ -65,24 +65,25 @@ check()
     fi
 
     for FILE in "$@"; do
-        cp "$FILE" "$FILE.bak"
+        cp -p "$FILE" "$FILE.bak"
     done
 
     "$SCRIPT"
 
     # Compare the script output to the old files and remove backups
     for FILE in "$@"; do
-        if ! diff "$FILE" "$FILE.bak" >/dev/null 2>&1; then
+        if diff "$FILE" "$FILE.bak" >/dev/null 2>&1; then
+            # Move the original file back so that $FILE's timestamp doesn't
+            # change (avoids spurious rebuilds with make).
+            mv "$FILE.bak" "$FILE"
+        else
             echo "'$FILE' was either modified or deleted by '$SCRIPT'"
             if [ -z "$UPDATE" ]; then
                 exit 1
+            else
+                rm "$FILE.bak"
             fi
         fi
-        if [ -z "$UPDATE" ]; then
-            mv "$FILE.bak" "$FILE"
-        else
-            rm "$FILE.bak"
-        fi
     done
 
     if [ -n "$directory" ]; then