nix: properly throw away tix files for postgrest-watch, resolves #1807

nix/devtools.nix

@@ -23,6 +23,7 @@ let
               postgrest-watch postgrest-test-io
 
           '';
+        redirectTixFiles = false; # will be done by sub-command
         inRootDir = true;
       }
       ''

nix/overlays/checked-shell-script/checked-shell-script.nix

@@ -9,7 +9,7 @@
 , stdenv
 , writeTextFile
 }:
-{ name, docs, inRootDir ? false, withTmpDir ? false }: text:
+{ name, docs, inRootDir ? false, redirectTixFiles ? true, withTmpDir ? false }: text:
 # TODO: do something sensible with docs, e.g. provide automated --help
 let
   bin =
@@ -22,14 +22,12 @@ let
         ''
           #!${runtimeShell}
           set -euo pipefail
-
-          # make sure that no script creates conflicting tix files
-          # postgrest-coverage will override HPCTIXFILE to make proper use of it
-          if test ! -v HPCTIXFILE; then
-            hpctixdir=$(mktemp -d)
-            export HPCTIXFILE="$hpctixdir"/postgrest.tix
-            trap 'rm -rf $hpctixdir' EXIT
-          fi
+        ''
+        + lib.optionalString redirectTixFiles ''
+          # storing tix files in a temporary throw away directory avoids mix/tix conflicts after changes
+          hpctixdir=$(mktemp -d)
+          export HPCTIXFILE="$hpctixdir"/postgrest.tix
+          trap 'rm -rf $hpctixdir' EXIT
         ''
         + lib.optionalString inRootDir ''
           cd "$(${git}/bin/git rev-parse --show-toplevel)"

nix/tests.nix

@@ -174,6 +174,7 @@ let
         inherit name;
         docs = "Run spec and io tests while collecting hpc coverage data.";
         inRootDir = true;
+        redirectTixFiles = false;
         withTmpDir = true;
       }
       ''

nix/withtmpdb.nix

@@ -7,6 +7,7 @@ checkedShellScript
   name = "postgrest-test-withtmpdb-${postgresql.name}";
   docs = "Run the given command in a temporary database";
   inRootDir = true;
+  redirectTixFiles = false;
 }
   ''
     # avoid starting multiple layers of with_tmp_db