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Unify and refactor value printing

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Previously, there were two mostly-identical value printers -- one in
`libexpr/eval.cc` (which didn't force values) and one in
`libcmd/repl.cc` (which did force values and also printed ANSI color
codes).

This PR unifies both of these printers into `print.cc` and provides a
`PrintOptions` struct for controlling the output, which allows for
toggling whether values are forced, whether repeated values are tracked,
and whether ANSI color codes are displayed.

Additionally, `PrintOptions` allows tuning the maximum number of
attributes, list items, and bytes in a string that will be displayed;
this makes it ideal for contexts where printing too much output (e.g.
all of Nixpkgs) is distracting. (As requested by @roberth in
https://github.com/NixOS/nix/pull/9554#issuecomment-1845095735)

Please read the tests for example output.

Future work:
- It would be nice to provide this function as a builtin, perhaps
  `builtins.toStringDebug` -- a printing function that never fails would
  be useful when debugging Nix code.
- It would be nice to support customizing `PrintOptions` members on the
  command line, e.g. `--option to-string-max-attrs 1000`.
This commit is contained in:
Rebecca Turner 2023-12-12 13:57:36 -08:00
parent c9125603a5
commit 0fa08b4516
No known key found for this signature in database
18 changed files with 1174 additions and 278 deletions
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158
src/libcmd/repl.cc
View file

@ -93,9 +93,17 @@ struct NixRepl
void evalString(std::string s, Value & v);
void loadDebugTraceEnv(DebugTrace & dt);
typedef std::set<Value *> ValuesSeen;
std::ostream & printValue(std::ostream & str, Value & v, unsigned int maxDepth);
std::ostream & printValue(std::ostream & str, Value & v, unsigned int maxDepth, ValuesSeen & seen);
void printValue(std::ostream & str,
Value & v,
unsigned int maxDepth = std::numeric_limits<unsigned int>::max())
{
::nix::printValue(*state, str, v, PrintOptions {
.ansiColors = true,
.force = true,
.derivationPaths = true,
.maxDepth = maxDepth
});
}
};
std::string removeWhitespace(std::string s)
@ -708,7 +716,8 @@ bool NixRepl::processLine(std::string line)
else if (command == ":p" || command == ":print") {
Value v;
evalString(arg, v);
printValue(std::cout, v, 1000000000) << std::endl;
printValue(std::cout, v);
std::cout << std::endl;
}
else if (command == ":q" || command == ":quit") {
@ -770,7 +779,8 @@ bool NixRepl::processLine(std::string line)
} else {
Value v;
evalString(line, v);
printValue(std::cout, v, 1) << std::endl;
printValue(std::cout, v, 1);
std::cout << std::endl;
}
}
@ -892,144 +902,6 @@ void NixRepl::evalString(std::string s, Value & v)
}
std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int maxDepth)
{
ValuesSeen seen;
return printValue(str, v, maxDepth, seen);
}
// FIXME: lot of cut&paste from Nix's eval.cc.
std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int maxDepth, ValuesSeen & seen)
{
str.flush();
checkInterrupt();
state->forceValue(v, v.determinePos(noPos));
switch (v.type()) {
case nInt:
str << ANSI_CYAN << v.integer << ANSI_NORMAL;
break;
case nBool:
str << ANSI_CYAN;
printLiteralBool(str, v.boolean);
str << ANSI_NORMAL;
break;
case nString:
str << ANSI_WARNING;
printLiteralString(str, v.string_view());
str << ANSI_NORMAL;
break;
case nPath:
str << ANSI_GREEN << v.path().to_string() << ANSI_NORMAL; // !!! escaping?
break;
case nNull:
str << ANSI_CYAN "null" ANSI_NORMAL;
break;
case nAttrs: {
seen.insert(&v);
bool isDrv = state->isDerivation(v);
if (isDrv) {
str << "«derivation ";
Bindings::iterator i = v.attrs->find(state->sDrvPath);
NixStringContext context;
if (i != v.attrs->end())
str << state->store->printStorePath(state->coerceToStorePath(i->pos, *i->value, context, "while evaluating the drvPath of a derivation"));
else
str << "???";
str << "»";
}
else if (maxDepth > 0) {
str << "{ ";
typedef std::map<std::string, Value *> Sorted;
Sorted sorted;
for (auto & i : *v.attrs)
sorted.emplace(state->symbols[i.name], i.value);
for (auto & i : sorted) {
printAttributeName(str, i.first);
str << " = ";
if (seen.count(i.second))
str << "«repeated»";
else
try {
printValue(str, *i.second, maxDepth - 1, seen);
} catch (AssertionError & e) {
str << ANSI_RED "«error: " << e.msg() << "»" ANSI_NORMAL;
}
str << "; ";
}
str << "}";
} else
str << "{ ... }";
break;
}
case nList:
seen.insert(&v);
str << "[ ";
if (maxDepth > 0)
for (auto elem : v.listItems()) {
if (seen.count(elem))
str << "«repeated»";
else
try {
printValue(str, *elem, maxDepth - 1, seen);
} catch (AssertionError & e) {
str << ANSI_RED "«error: " << e.msg() << "»" ANSI_NORMAL;
}
str << " ";
}
else
str << "... ";
str << "]";
break;
case nFunction:
if (v.isLambda()) {
std::ostringstream s;
s << state->positions[v.lambda.fun->pos];
str << ANSI_BLUE "«lambda @ " << filterANSIEscapes(s.str()) << "»" ANSI_NORMAL;
} else if (v.isPrimOp()) {
str << ANSI_MAGENTA "«primop»" ANSI_NORMAL;
} else if (v.isPrimOpApp()) {
str << ANSI_BLUE "«primop-app»" ANSI_NORMAL;
} else {
abort();
}
break;
case nFloat:
str << v.fpoint;
break;
case nThunk:
case nExternal:
default:
str << ANSI_RED "«unknown»" ANSI_NORMAL;
break;
}
return str;
}
std::unique_ptr<AbstractNixRepl> AbstractNixRepl::create(
const SearchPath & searchPath, nix::ref<Store> store, ref<EvalState> state,
std::function<AnnotatedValues()> getValues)