fix(users/edef/depot-scan): properly trace readFile/readDir r/1590

Change-Id: I493e7d20504d34f83a53db50b69e86668874756e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1651
Reviewed-by: edef <edef@edef.eu>
Tested-by: BuildkiteCI

3 files changed, 19 insertions, 2 deletions

diff --git a/users/edef/depot-scan-wrap.nix b/users/edef/depot-scan-wrap.nix
new file mode 100644
index 0000000000..52ea5cc852
--- /dev/null
+++ b/users/edef/depot-scan-wrap.nix
@@ -0,0 +1,17 @@
+# this wraps import to override readFile and readDir to trace the files it touches
+# technique inspired by lorri
+{ ... }:
+
+let
+
+  global = {
+    import = global.scopedImport {};
+    scopedImport = x: builtins.scopedImport (global // x);
+    builtins = builtins // {
+      inherit (global) import scopedImport;
+      readFile = path: builtins.trace "depot-scan '${toString path}'" (builtins.readFile path);
+      readDir  = path: builtins.trace "depot-scan '${toString path}'" (builtins.readDir  path);
+    };
+  };
+
+in global.import
diff --git a/users/edef/depot-scan.nix b/users/edef/depot-scan.nix
index ce0f8d9799..f0654188c8 100644
--- a/users/edef/depot-scan.nix
+++ b/users/edef/depot-scan.nix
@@ -8,5 +8,5 @@ pkgs.writeShellScriptBin "depot-scan" ''
   attr="''${path//\//.}"
   root="$(git rev-parse --show-toplevel)"
   echo "scanning //$path" >&2
-  nix-instantiate "$root" -A "$attr" -vv 2> >(${pkgs.perl}/bin/perl ${./depot-scan.pl}) >&2
+  nix-instantiate -E "import ${./depot-scan-wrap.nix} {} $root" -A "$attr" -vv 2> >(${pkgs.perl}/bin/perl ${./depot-scan.pl}) >&2
 ''
diff --git a/users/edef/depot-scan.pl b/users/edef/depot-scan.pl
index 39550d83c1..8808e2eb00 100755
--- a/users/edef/depot-scan.pl
+++ b/users/edef/depot-scan.pl
@@ -3,7 +3,7 @@ use strict;
 
 if (/^evaluating file '(.*)'$/ or
     /^copied source '(.*)' -> '.*'$/ or
-    /^trace: lorri read: '(.*)'$/) {
+    /^trace: depot-scan '(.*)'$/) {
     print $1;
     next;
 }