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)))) {

1 files changed, 13 insertions, 22 deletions

diff --git a/src/libutil/tests/logging.cc b/src/libutil/tests/logging.cc
index 5b32c84a4..d990e5499 100644
--- a/src/libutil/tests/logging.cc
+++ b/src/libutil/tests/logging.cc
@@ -1,3 +1,5 @@
+#if 0
+
 #include "logging.hh"
 #include "nixexpr.hh"
 #include "util.hh"
@@ -41,8 +43,7 @@ namespace nix {
 
         makeJSONLogger(*logger)->logEI({
                 .name = "error name",
-                .description = "error without any code lines.",
-                .hint = hintfmt("this hint has %1% templated %2%!!",
+                .msg = hintfmt("this hint has %1% templated %2%!!",
                     "yellow",
                     "values"),
                 .errPos = Pos(foFile, problem_file, 02, 13)
@@ -62,7 +63,7 @@ namespace nix {
             throw TestError(e.info());
         } catch (Error &e) {
             ErrorInfo ei = e.info();
-            ei.hint = hintfmt("%s; subsequent error message.", normaltxt(e.info().hint ? e.info().hint->str() : ""));
+            ei.msg = hintfmt("%s; subsequent error message.", normaltxt(e.info().msg.str()));
 
             testing::internal::CaptureStderr();
             logger->logEI(ei);
@@ -95,7 +96,6 @@ namespace nix {
 
         logger->logEI({ .level = lvlInfo,
                         .name = "Info name",
-                        .description = "Info description",
             });
 
         auto str = testing::internal::GetCapturedStderr();
@@ -109,7 +109,6 @@ namespace nix {
 
         logger->logEI({ .level = lvlTalkative,
                         .name = "Talkative name",
-                        .description = "Talkative description",
             });
 
         auto str = testing::internal::GetCapturedStderr();
@@ -123,7 +122,6 @@ namespace nix {
 
         logger->logEI({ .level = lvlChatty,
                         .name = "Chatty name",
-                        .description = "Talkative description",
             });
 
         auto str = testing::internal::GetCapturedStderr();
@@ -137,7 +135,6 @@ namespace nix {
 
         logger->logEI({ .level = lvlDebug,
                         .name = "Debug name",
-                        .description = "Debug description",
             });
 
         auto str = testing::internal::GetCapturedStderr();
@@ -151,7 +148,6 @@ namespace nix {
 
         logger->logEI({ .level = lvlVomit,
                         .name = "Vomit name",
-                        .description = "Vomit description",
             });
 
         auto str = testing::internal::GetCapturedStderr();
@@ -167,7 +163,6 @@ namespace nix {
 
         logError({
                 .name = "name",
-                .description = "error description",
             });
 
         auto str = testing::internal::GetCapturedStderr();
@@ -182,8 +177,7 @@ namespace nix {
 
         logError({
                 .name = "error name",
-                .description = "error with code lines",
-                .hint = hintfmt("this hint has %1% templated %2%!!",
+                .msg = hintfmt("this hint has %1% templated %2%!!",
                     "yellow",
                     "values"),
                 .errPos = Pos(foString, problem_file, 02, 13),
@@ -200,8 +194,7 @@ namespace nix {
 
         logError({
                 .name = "error name",
-                .description = "error without any code lines.",
-                .hint = hintfmt("this hint has %1% templated %2%!!",
+                .msg = hintfmt("this hint has %1% templated %2%!!",
                     "yellow",
                     "values"),
                 .errPos = Pos(foFile, problem_file, 02, 13)
@@ -216,7 +209,7 @@ namespace nix {
 
         logError({
                 .name = "error name",
-                .hint = hintfmt("hint %1%", "only"),
+                .msg = hintfmt("hint %1%", "only"),
             });
 
         auto str = testing::internal::GetCapturedStderr();
@@ -233,8 +226,7 @@ namespace nix {
 
         logWarning({
                 .name = "name",
-                .description = "warning description",
-                .hint = hintfmt("there was a %1%", "warning"),
+                .msg = hintfmt("there was a %1%", "warning"),
             });
 
         auto str = testing::internal::GetCapturedStderr();
@@ -250,8 +242,7 @@ namespace nix {
 
         logWarning({
                 .name = "warning name",
-                .description = "warning description",
-                .hint = hintfmt("this hint has %1% templated %2%!!",
+                .msg = hintfmt("this hint has %1% templated %2%!!",
                     "yellow",
                     "values"),
                 .errPos = Pos(foStdin, problem_file, 2, 13),
@@ -274,8 +265,7 @@ namespace nix {
 
         auto e = AssertionError(ErrorInfo {
                 .name = "wat",
-                .description = "show-traces",
-                .hint = hintfmt("it has been %1% days since our last error", "zero"),
+                .msg = hintfmt("it has been %1% days since our last error", "zero"),
                 .errPos = Pos(foString, problem_file, 2, 13),
             });
 
@@ -301,8 +291,7 @@ namespace nix {
 
         auto e = AssertionError(ErrorInfo {
                 .name = "wat",
-                .description = "hide traces",
-                .hint = hintfmt("it has been %1% days since our last error", "zero"),
+                .msg = hintfmt("it has been %1% days since our last error", "zero"),
                 .errPos = Pos(foString, problem_file, 2, 13),
             });
 
@@ -377,3 +366,5 @@ namespace nix {
     }
 
 }
+
+#endif