From f0e52f31cd33fd321f71eda0bc1d6cd965b5997c Mon Sep 17 00:00:00 2001
From: Profpatsch <mail@profpatsch.de>
Date: Thu, 5 May 2022 21:08:54 +0200
Subject: feat(users/Profpatsch/importDhall): print type annotation
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If no type annotation is given, debugging errors gets a lot harder
because there is nothing to compare it against.

But we can tell dhall to print the type first (this means double
evaluation, but that’s an optimization problem to be solved later).

Change-Id: Icf793828070cd6bb8daeb4c07de3162a5e064653
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5525
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>
---
 users/Profpatsch/importDhall.nix | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

(limited to 'users/Profpatsch')

diff --git a/users/Profpatsch/importDhall.nix b/users/Profpatsch/importDhall.nix
index 9713b2cfb8..bddfcc5b07 100644
--- a/users/Profpatsch/importDhall.nix
+++ b/users/Profpatsch/importDhall.nix
@@ -37,7 +37,8 @@ let
       cache = ".cache";
       cacheDhall = "${cache}/dhall";
 
-      typeAnnot = if type == null then "" else ": ${type}";
+      hadTypeAnnot = type != null;
+      typeAnnot = lib.optionalString hadTypeAnnot ": ${type}";
 
       convert = pkgs.runCommandLocal "dhall-to-nix" { inherit deps; } ''
         mkdir -p ${cacheDhall}
@@ -49,9 +50,19 @@ let
         # go into the source directory, so that the type can import files.
         # TODO: This is a bit of a hack hrm.
         cd "${src}"
-        printf '%s' ${lib.escapeShellArg "${src}/${main} ${typeAnnot}"} \
-          | ${pkgs.dhall-nix}/bin/dhall-to-nix \
-          > $out
+        ${if hadTypeAnnot then ''
+            printf '%s' ${lib.escapeShellArg "${src}/${main} ${typeAnnot}"} \
+              | ${pkgs.dhall-nix}/bin/dhall-to-nix \
+              > $out
+          ''
+          else ''
+            printf 'No type annotation given, the dhall expression type was:\n'
+            ${pkgs.dhall}/bin/dhall type --file "${src}/${main}"
+            printf '%s' ${lib.escapeShellArg "${src}/${main}"} \
+              | ${pkgs.dhall-nix}/bin/dhall-to-nix \
+              > $out
+          ''}
+
       '';
     in
     import convert;
-- 
cgit 1.4.1