lix/src/libutil/error.hh
Eelco Dolstra 8d4268d190 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)))) {
2021-01-21 11:02:09 +01:00

209 lines
4.8 KiB
C++

#pragma once
#include "ref.hh"
#include "types.hh"
#include "fmt.hh"
#include <cstring>
#include <list>
#include <memory>
#include <map>
#include <optional>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
/* Before 4.7, gcc's std::exception uses empty throw() specifiers for
* its (virtual) destructor and what() in c++11 mode, in violation of spec
*/
#ifdef __GNUC__
#if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 7)
#define EXCEPTION_NEEDS_THROW_SPEC
#endif
#endif
namespace nix {
/*
This file defines two main structs/classes used in nix error handling.
ErrorInfo provides a standard payload of error information, with conversion to string
happening in the logger rather than at the call site.
BaseError is the ancestor of nix specific exceptions (and Interrupted), and contains
an ErrorInfo.
ErrorInfo structs are sent to the logger as part of an exception, or directly with the
logError or logWarning macros.
See libutil/tests/logging.cc for usage examples.
*/
typedef enum {
lvlError = 0,
lvlWarn,
lvlNotice,
lvlInfo,
lvlTalkative,
lvlChatty,
lvlDebug,
lvlVomit
} Verbosity;
typedef enum {
foFile,
foStdin,
foString
} FileOrigin;
// the lines of code surrounding an error.
struct LinesOfCode {
std::optional<string> prevLineOfCode;
std::optional<string> errLineOfCode;
std::optional<string> nextLineOfCode;
};
// ErrPos indicates the location of an error in a nix file.
struct ErrPos {
int line = 0;
int column = 0;
string file;
FileOrigin origin;
operator bool() const
{
return line != 0;
}
// convert from the Pos struct, found in libexpr.
template <class P>
ErrPos& operator=(const P &pos)
{
origin = pos.origin;
line = pos.line;
column = pos.column;
// is file symbol null?
if (pos.file.set())
file = pos.file;
else
file = "";
return *this;
}
template <class P>
ErrPos(const P &p)
{
*this = p;
}
};
struct Trace {
std::optional<ErrPos> pos;
hintformat hint;
};
struct ErrorInfo {
Verbosity level;
string name; // FIXME: rename
hintformat msg;
std::optional<ErrPos> errPos;
std::list<Trace> traces;
static std::optional<string> programName;
};
std::ostream& showErrorInfo(std::ostream &out, const ErrorInfo &einfo, bool showTrace);
/* BaseError should generally not be caught, as it has Interrupted as
a subclass. Catch Error instead. */
class BaseError : public std::exception
{
protected:
mutable ErrorInfo err;
mutable std::optional<string> what_;
const string& calcWhat() const;
public:
unsigned int status = 1; // exit status
template<typename... Args>
BaseError(unsigned int status, const Args & ... args)
: err { .level = lvlError, .msg = hintfmt(args...) }
, status(status)
{ }
template<typename... Args>
BaseError(const std::string & fs, const Args & ... args)
: err { .level = lvlError, .msg = hintfmt(fs, args...) }
{ }
BaseError(hintformat hint)
: err { .level = lvlError, .msg = hint }
{ }
BaseError(ErrorInfo && e)
: err(std::move(e))
{ }
BaseError(const ErrorInfo & e)
: err(e)
{ }
virtual const char* sname() const { return "BaseError"; }
#ifdef EXCEPTION_NEEDS_THROW_SPEC
~BaseError() throw () { };
const char * what() const throw () { return calcWhat().c_str(); }
#else
const char * what() const noexcept override { return calcWhat().c_str(); }
#endif
const string & msg() const { return calcWhat(); }
const ErrorInfo & info() const { calcWhat(); return err; }
template<typename... Args>
BaseError & addTrace(std::optional<ErrPos> e, const string &fs, const Args & ... args)
{
return addTrace(e, hintfmt(fs, args...));
}
BaseError & addTrace(std::optional<ErrPos> e, hintformat hint);
bool hasTrace() const { return !err.traces.empty(); }
};
#define MakeError(newClass, superClass) \
class newClass : public superClass \
{ \
public: \
using superClass::superClass; \
virtual const char* sname() const override { return #newClass; } \
}
MakeError(Error, BaseError);
MakeError(UsageError, Error);
MakeError(UnimplementedError, Error);
class SysError : public Error
{
public:
int errNo;
template<typename... Args>
SysError(const Args & ... args)
: Error("")
{
errNo = errno;
auto hf = hintfmt(args...);
err.msg = hintfmt("%1%: %2%", normaltxt(hf.str()), strerror(errNo));
}
virtual const char* sname() const override { return "SysError"; }
};
}