build-support: Use mktemp -d in nix-prefetch-*.

Instead of relying on $$ to not collide with an existing path.

Quoting the Bash manual about $$:

> Expands to the process ID of the shell. In a () subshell, it expands
> to the process ID of the current shell, not the subshell.

So, this is different from $BASHPID:

> Expands to the process ID of the current bash process. This differs
> from $$ under certain circumstances, such as subshells that do not
> require bash to be re-initialized.

But even $BASHPID is prone to race conditions if the process IDs wrap
around, so to be on the safe side, we're using mktemp here.

Closes #3784.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

1 files changed, 3 insertions, 4 deletions

diff --git a/pkgs/build-support/fetchsvn/nix-prefetch-svn b/pkgs/build-support/fetchsvn/nix-prefetch-svn
index a2ee3ac6052f..74de0a14c801 100755
--- a/pkgs/build-support/fetchsvn/nix-prefetch-svn
+++ b/pkgs/build-support/fetchsvn/nix-prefetch-svn
@@ -41,11 +41,10 @@ fi
 # If we don't know the hash or a path with that hash doesn't exist,
 # download the file and add it to the store.
 if test -z "$finalPath"; then
-    tmpPath=/tmp/svn-checkout-tmp-$$
-    tmpFile=$tmpPath/$dstFile
-    mkdir $tmpPath
+    tmpPath="$(mktemp --tmpdir -d svn-checkout-tmp-XXXXXXXX)"
+    trap "rm -rf \"$tmpPath\"" EXIT
 
-    trap "rm -rf $tmpPath" EXIT
+    tmpFile="$tmpPath/$dstFile"
 
     # Perform the checkout.
     if test "$NIX_PREFETCH_SVN_LEAVE_DOT_SVN" != 1