From 8d4268d1901452164b3e666f2eb6bd6bf516493b Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Thu, 21 Jan 2021 00:27:36 +0100
Subject: Improve error formatting
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Changes:

* The divider lines are gone. These were in practice a bit confusing,
  in particular with --show-trace or --keep-going, since then there
  were multiple lines, suggesting a start/end which wasn't the case.

* Instead, multi-line error messages are now indented to align with
  the prefix (e.g. "error: ").

* The 'description' field is gone since we weren't really using it.

* 'hint' is renamed to 'msg' since it really wasn't a hint.

* The error is now printed *before* the location info.

* The 'name' field is no longer printed since most of the time it
  wasn't very useful since it was just the name of the exception (like
  EvalError). Ideally in the future this would be a unique, easily
  googleable error ID (like rustc).

* "trace:" is now just "…". This assumes error contexts start with
  something like "while doing X".

Example before:

  error: --- AssertionError ---------------------------------------------------------------------------------------- nix
  at: (7:7) in file: /home/eelco/Dev/nixpkgs/pkgs/applications/misc/hello/default.nix

       6|
       7|   x = assert false; 1;
        |       ^
       8|

  assertion 'false' failed
  ----------------------------------------------------- show-trace -----------------------------------------------------
  trace: while evaluating the attribute 'x' of the derivation 'hello-2.10'
  at: (192:11) in file: /home/eelco/Dev/nixpkgs/pkgs/stdenv/generic/make-derivation.nix

     191|         // (lib.optionalAttrs (!(attrs ? name) && attrs ? pname && attrs ? version)) {
     192|           name = "${attrs.pname}-${attrs.version}";
        |           ^
     193|         } // (lib.optionalAttrs (stdenv.hostPlatform != stdenv.buildPlatform && !dontAddHostSuffix && (attrs ? name || (attrs ? pname && attrs ? version)))) {

Example after:

  error: assertion 'false' failed

         at: (7:7) in file: /home/eelco/Dev/nixpkgs/pkgs/applications/misc/hello/default.nix

              6|
              7|   x = assert false; 1;
               |       ^
              8|

         … while evaluating the attribute 'x' of the derivation 'hello-2.10'

         at: (192:11) in file: /home/eelco/Dev/nixpkgs/pkgs/stdenv/generic/make-derivation.nix

            191|         // (lib.optionalAttrs (!(attrs ? name) && attrs ? pname && attrs ? version)) {
            192|           name = "${attrs.pname}-${attrs.version}";
               |           ^
            193|         } // (lib.optionalAttrs (stdenv.hostPlatform != stdenv.buildPlatform && !dontAddHostSuffix && (attrs ? name || (attrs ? pname && attrs ? version)))) {
---
 src/libutil/serialise.cc | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

(limited to 'src/libutil/serialise.cc')

diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 87c1099a1..d1a16b6ba 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -52,10 +52,7 @@ size_t threshold = 256 * 1024 * 1024;
 
 static void warnLargeDump()
 {
-    logWarning({
-        .name = "Large path",
-        .description = "dumping very large path (> 256 MiB); this may run out of memory"
-    });
+    warn("dumping very large path (> 256 MiB); this may run out of memory");
 }
 
 
@@ -306,8 +303,7 @@ Sink & operator << (Sink & sink, const Error & ex)
         << "Error"
         << info.level
         << info.name
-        << info.description
-        << (info.hint ? info.hint->str() : "")
+        << info.msg.str()
         << 0 // FIXME: info.errPos
         << info.traces.size();
     for (auto & trace : info.traces) {
@@ -374,12 +370,14 @@ Error readError(Source & source)
 {
     auto type = readString(source);
     assert(type == "Error");
-    ErrorInfo info;
-    info.level = (Verbosity) readInt(source);
-    info.name = readString(source);
-    info.description = readString(source);
-    auto hint = readString(source);
-    if (hint != "") info.hint = hintformat(std::move(format("%s") % hint));
+    auto level = (Verbosity) readInt(source);
+    auto name = readString(source);
+    auto msg = readString(source);
+    ErrorInfo info {
+        .level = level,
+        .name = name,
+        .msg = hintformat(std::move(format("%s") % msg)),
+    };
     auto havePos = readNum<size_t>(source);
     assert(havePos == 0);
     auto nrTraces = readNum<size_t>(source);
-- 
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