Improve error formatting

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)))) {

3 files changed, 8 insertions, 20 deletions

diff --git a/src/nix/daemon.cc b/src/nix/daemon.cc
index 204d4ce6b..a358cb0d9 100644
--- a/src/nix/daemon.cc
+++ b/src/nix/daemon.cc
@@ -258,8 +258,8 @@ static void daemonLoop()
             return;
         } catch (Error & error) {
             ErrorInfo ei = error.info();
-            ei.hint = std::optional(hintfmt("error processing connection: %1%",
-                (error.info().hint.has_value() ? error.info().hint->str() : "")));
+            // FIXME: add to trace?
+            ei.msg = hintfmt("error processing connection: %1%", ei.msg.str());
             logError(ei);
         }
     }
diff --git a/src/nix/upgrade-nix.cc b/src/nix/upgrade-nix.cc
index 299ea40aa..9cd567896 100644
--- a/src/nix/upgrade-nix.cc
+++ b/src/nix/upgrade-nix.cc
@@ -61,10 +61,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
 
         if (dryRun) {
             stopProgressBar();
-            logWarning({
-                .name = "Version update",
-                .hint = hintfmt("would upgrade to version %s", version)
-            });
+            warn("would upgrade to version %s", version);
             return;
         }
 
diff --git a/src/nix/verify.cc b/src/nix/verify.cc
index b2963cf74..9b04e032a 100644
--- a/src/nix/verify.cc
+++ b/src/nix/verify.cc
@@ -101,14 +101,10 @@ struct CmdVerify : StorePathsCommand
                     if (hash.first != info->narHash) {
                         corrupted++;
                         act2.result(resCorruptedPath, store->printStorePath(info->path));
-                        logError({
-                            .name = "Hash error - path modified",
-                            .hint = hintfmt(
-                                "path '%s' was modified! expected hash '%s', got '%s'",
-                                store->printStorePath(info->path),
-                                info->narHash.to_string(Base32, true),
-                                hash.first.to_string(Base32, true))
-                        });
+                        printError("path '%s' was modified! expected hash '%s', got '%s'",
+                            store->printStorePath(info->path),
+                            info->narHash.to_string(Base32, true),
+                            hash.first.to_string(Base32, true));
                     }
                 }
 
@@ -156,12 +152,7 @@ struct CmdVerify : StorePathsCommand
                     if (!good) {
                         untrusted++;
                         act2.result(resUntrustedPath, store->printStorePath(info->path));
-                        logError({
-                            .name = "Untrusted path",
-                            .hint = hintfmt("path '%s' is untrusted",
-                                store->printStorePath(info->path))
-                        });
-
+                        printError("path '%s' is untrusted", store->printStorePath(info->path));
                     }
 
                 }