374 lines
12 KiB
C++
374 lines
12 KiB
C++
#include "error.hh"
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#include "environment-variables.hh"
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#include "signals.hh"
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#include "terminal.hh"
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#include <iostream>
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#include <optional>
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#include "serialise.hh"
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#include <sstream>
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namespace nix {
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void BaseError::addTrace(std::shared_ptr<AbstractPos> && e, hintformat hint, bool frame)
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{
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err.traces.push_front(Trace { .pos = std::move(e), .hint = hint, .frame = frame });
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}
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void throwExceptionSelfCheck(){
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// This is meant to be caught in initLibUtil()
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throw SysError("C++ exception handling is broken. This would appear to be a problem with the way Nix was compiled and/or linked and/or loaded.");
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}
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// c++ std::exception descendants must have a 'const char* what()' function.
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// This stringifies the error and caches it for use by what(), or similarly by msg().
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const std::string & BaseError::calcWhat() const
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{
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if (what_.has_value())
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return *what_;
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else {
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std::ostringstream oss;
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showErrorInfo(oss, err, loggerSettings.showTrace);
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what_ = oss.str();
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return *what_;
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}
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}
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std::optional<std::string> ErrorInfo::programName = std::nullopt;
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std::ostream & operator <<(std::ostream & os, const hintformat & hf)
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{
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return os << hf.str();
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}
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std::ostream & operator <<(std::ostream & str, const AbstractPos & pos)
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{
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pos.print(str);
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str << ":" << pos.line;
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if (pos.column > 0)
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str << ":" << pos.column;
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return str;
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}
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std::optional<LinesOfCode> AbstractPos::getCodeLines() const
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{
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if (line == 0)
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return std::nullopt;
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if (auto source = getSource()) {
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std::istringstream iss(*source);
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// count the newlines.
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int count = 0;
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std::string curLine;
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int pl = line - 1;
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LinesOfCode loc;
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do {
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std::getline(iss, curLine);
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++count;
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if (count < pl)
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;
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else if (count == pl) {
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loc.prevLineOfCode = curLine;
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} else if (count == pl + 1) {
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loc.errLineOfCode = curLine;
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} else if (count == pl + 2) {
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loc.nextLineOfCode = curLine;
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break;
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}
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if (!iss.good())
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break;
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} while (true);
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return loc;
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}
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return std::nullopt;
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}
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// print lines of code to the ostream, indicating the error column.
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void printCodeLines(std::ostream & out,
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const std::string & prefix,
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const AbstractPos & errPos,
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const LinesOfCode & loc)
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{
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// previous line of code.
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if (loc.prevLineOfCode.has_value()) {
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out << std::endl
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<< fmt("%1% %|2$5d|| %3%",
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prefix,
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(errPos.line - 1),
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*loc.prevLineOfCode);
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}
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if (loc.errLineOfCode.has_value()) {
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// line of code containing the error.
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out << std::endl
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<< fmt("%1% %|2$5d|| %3%",
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prefix,
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(errPos.line),
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*loc.errLineOfCode);
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// error arrows for the column range.
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if (errPos.column > 0) {
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int start = errPos.column;
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std::string spaces;
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for (int i = 0; i < start; ++i) {
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spaces.append(" ");
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}
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std::string arrows("^");
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out << std::endl
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<< fmt("%1% |%2%" ANSI_RED "%3%" ANSI_NORMAL,
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prefix,
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spaces,
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arrows);
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}
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}
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// next line of code.
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if (loc.nextLineOfCode.has_value()) {
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out << std::endl
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<< fmt("%1% %|2$5d|| %3%",
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prefix,
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(errPos.line + 1),
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*loc.nextLineOfCode);
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}
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}
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static std::string indent(std::string_view indentFirst, std::string_view indentRest, std::string_view s)
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{
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std::string res;
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bool first = true;
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while (!s.empty()) {
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auto end = s.find('\n');
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if (!first) res += "\n";
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res += chomp(std::string(first ? indentFirst : indentRest) + std::string(s.substr(0, end)));
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first = false;
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if (end == s.npos) break;
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s = s.substr(end + 1);
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}
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return res;
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}
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/**
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* A development aid for finding missing positions, to improve error messages. Example use:
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*
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* NIX_DEVELOPER_SHOW_UNKNOWN_LOCATIONS=1 _NIX_TEST_ACCEPT=1 make tests/lang.sh.test
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* git diff -U20 tests
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*
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*/
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static bool printUnknownLocations = getEnv("_NIX_DEVELOPER_SHOW_UNKNOWN_LOCATIONS").has_value();
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/**
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* Print a position, if it is known.
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*
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* @return true if a position was printed.
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*/
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static bool printPosMaybe(std::ostream & oss, std::string_view indent, const std::shared_ptr<AbstractPos> & pos) {
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bool hasPos = pos && *pos;
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if (hasPos) {
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oss << "\n" << indent << ANSI_BLUE << "at " ANSI_WARNING << *pos << ANSI_NORMAL << ":";
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if (auto loc = pos->getCodeLines()) {
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oss << "\n";
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printCodeLines(oss, "", *pos, *loc);
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oss << "\n";
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}
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} else if (printUnknownLocations) {
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oss << "\n" << indent << ANSI_BLUE << "at " ANSI_RED << "UNKNOWN LOCATION" << ANSI_NORMAL << "\n";
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}
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return hasPos;
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}
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std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool showTrace)
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{
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std::string prefix;
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switch (einfo.level) {
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case Verbosity::lvlError: {
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prefix = ANSI_RED "error";
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break;
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}
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case Verbosity::lvlNotice: {
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prefix = ANSI_RED "note";
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break;
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}
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case Verbosity::lvlWarn: {
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prefix = ANSI_WARNING "warning";
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break;
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}
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case Verbosity::lvlInfo: {
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prefix = ANSI_GREEN "info";
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break;
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}
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case Verbosity::lvlTalkative: {
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prefix = ANSI_GREEN "talk";
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break;
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}
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case Verbosity::lvlChatty: {
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prefix = ANSI_GREEN "chat";
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break;
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}
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case Verbosity::lvlVomit: {
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prefix = ANSI_GREEN "vomit";
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break;
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}
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case Verbosity::lvlDebug: {
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prefix = ANSI_WARNING "debug";
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break;
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}
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default:
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assert(false);
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}
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// FIXME: show the program name as part of the trace?
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if (einfo.programName && einfo.programName != ErrorInfo::programName)
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prefix += fmt(" [%s]:" ANSI_NORMAL " ", einfo.programName.value_or(""));
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else
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prefix += ":" ANSI_NORMAL " ";
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std::ostringstream oss;
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/*
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* Traces
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* ------
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*
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* The semantics of traces is a bit weird. We have only one option to
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* print them and to make them verbose (--show-trace). In the code they
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* are always collected, but they are not printed by default. The code
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* also collects more traces when the option is on. This means that there
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* is no way to print the simplified traces at all.
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*
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* I (layus) designed the code to attach positions to a restricted set of
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* messages. This means that we have a lot of traces with no position at
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* all, including most of the base error messages. For example "type
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* error: found a string while a set was expected" has no position, but
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* will come with several traces detailing it's precise relation to the
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* closest know position. This makes erroring without printing traces
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* quite useless.
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*
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* This is why I introduced the idea to always print a few traces on
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* error. The number 3 is quite arbitrary, and was selected so as not to
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* clutter the console on error. For the same reason, a trace with an
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* error position takes more space, and counts as two traces towards the
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* limit.
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*
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* The rest is truncated, unless --show-trace is passed. This preserves
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* the same bad semantics of --show-trace to both show the trace and
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* augment it with new data. Not too sure what is the best course of
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* action.
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*
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* The issue is that it is fundamentally hard to provide a trace for a
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* lazy language. The trace will only cover the current spine of the
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* evaluation, missing things that have been evaluated before. For
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* example, most type errors are hard to inspect because there is not
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* trace for the faulty value. These errors should really print the faulty
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* value itself.
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*
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* In function calls, the --show-trace flag triggers extra traces for each
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* function invocation. These work as scopes, allowing to follow the
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* current spine of the evaluation graph. Without that flag, the error
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* trace should restrict itself to a restricted prefix of that trace,
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* until the first scope. If we ever get to such a precise error
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* reporting, there would be no need to add an arbitrary limit here. We
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* could always print the full trace, and it would just be small without
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* the flag.
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*
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* One idea I had is for XxxError.addTrace() to perform nothing if one
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* scope has already been traced. Alternatively, we could stop here when
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* we encounter such a scope instead of after an arbitrary number of
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* traces. This however requires to augment traces with the notion of
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* "scope".
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*
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* This is particularly visible in code like evalAttrs(...) where we have
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* to make a decision between the two following options.
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*
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* ``` long traces
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* inline void EvalState::evalAttrs(Env & env, Expr * e, Value & v, const Pos & pos, std::string_view errorCtx)
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* {
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* try {
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* e->eval(*this, env, v);
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* if (v.type() != nAttrs)
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* throwTypeError("value is %1% while a set was expected", v);
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* } catch (Error & e) {
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* e.addTrace(pos, errorCtx);
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* throw;
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* }
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* }
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* ```
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*
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* ``` short traces
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* inline void EvalState::evalAttrs(Env & env, Expr * e, Value & v, const Pos & pos, std::string_view errorCtx)
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* {
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* e->eval(*this, env, v);
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* try {
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* if (v.type() != nAttrs)
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* throwTypeError("value is %1% while a set was expected", v);
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* } catch (Error & e) {
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* e.addTrace(pos, errorCtx);
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* throw;
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* }
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* }
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* ```
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*
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* The second example can be rewritten more concisely, but kept in this
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* form to highlight the symmetry. The first option adds more information,
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* because whatever caused an error down the line, in the generic eval
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* function, will get annotated with the code location that uses and
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* required it. The second option is less verbose, but does not provide
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* any context at all as to where and why a failing value was required.
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*
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* Scopes would fix that, by adding context only when --show-trace is
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* passed, and keeping the trace terse otherwise.
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*
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*/
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// Enough indent to align with with the `... `
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// prepended to each element of the trace
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auto ellipsisIndent = " ";
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bool frameOnly = false;
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if (!einfo.traces.empty()) {
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size_t count = 0;
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for (const auto & trace : einfo.traces) {
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if (trace.hint.str().empty()) continue;
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if (frameOnly && !trace.frame) continue;
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if (!showTrace && count > 3) {
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oss << "\n" << ANSI_WARNING "(stack trace truncated; use '--show-trace' to show the full trace)" ANSI_NORMAL << "\n";
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break;
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}
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count++;
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frameOnly = trace.frame;
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oss << "\n" << "… " << trace.hint.str() << "\n";
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if (printPosMaybe(oss, ellipsisIndent, trace.pos))
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count++;
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}
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oss << "\n" << prefix;
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}
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oss << einfo.msg << "\n";
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printPosMaybe(oss, "", einfo.errPos);
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auto suggestions = einfo.suggestions.trim();
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if (!suggestions.suggestions.empty()) {
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oss << "Did you mean " <<
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suggestions.trim() <<
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"?" << std::endl;
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}
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out << indent(prefix, std::string(filterANSIEscapes(prefix, true).size(), ' '), chomp(oss.str()));
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return out;
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}
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}
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