Git fetcher: Don't compute lastModified if it's already specified

Same as revCount.

Author: edolstra

src/libfetchers/fetchers.cc

@@ -276,15 +276,6 @@ void Input::checkLocks(Input specified, Input & result)
         }
     }
 
-    if (auto prevLastModified = specified.getLastModified()) {
-        if (result.getLastModified() != prevLastModified)
-            throw Error(
-                "'lastModified' attribute mismatch in input '%s', expected %d, got %d",
-                result.to_string(),
-                *prevLastModified,
-                result.getLastModified().value_or(-1));
-    }
-
     if (auto prevRev = specified.getRev()) {
         if (result.getRev() != prevRev)
             throw Error("'rev' attribute mismatch in input '%s', expected %s", result.to_string(), prevRev->gitRev());

src/libfetchers/git.cc

@@ -738,12 +738,14 @@ struct GitInputScheme : InputScheme
 
         auto rev = *input.getRev();
 
-        input.attrs.insert_or_assign("lastModified", getLastModified(settings, repoInfo, repoDir, rev));
+        /* Skip lastModified computation if it's already supplied by the caller.
+           We don't care if they specify an incorrect value; it doesn't
+           matter for security, unlike narHash. */
+        if (!input.attrs.contains("lastModified"))
+            input.attrs.insert_or_assign("lastModified", getLastModified(settings, repoInfo, repoDir, rev));
 
         if (!getShallowAttr(input)) {
-            /* Skip revCount computation if it's already supplied by the caller.
-               We don't care if they specify an incorrect value; it doesn't
-               matter for security, unlike narHash. */
+            /* Like lastModified, skip revCount if supplied by the caller. */
             if (!input.attrs.contains("revCount"))
                 input.attrs.insert_or_assign("revCount", getRevCount(settings, repoInfo, repoDir, rev));
         }