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Print top-level errors normally in nix repl

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Previously, errors while printing values in `nix repl` would be printed
in `«error: ...»` brackets rather than displayed normally:

```
nix-repl> legacyPackages.aarch64-darwin.pythonPackages.APScheduler
«error: Package ‘python-2.7.18.7’ in /nix/store/6s0m1qc31zw3l3kq0q4wd5cp3lqpkq0q-source/pkgs/development/interpreters/python/cpython/2.7/default.nix:335 is marked as insecure, refusing to evaluate.»
```

Now, errors will be displayed normally if they're emitted at the
top-level of an expression:

```
nix-repl> legacyPackages.aarch64-darwin.pythonPackages.APScheduler
error:
       … in the condition of the assert statement
         at /nix/store/6s0m1qc31zw3l3kq0q4wd5cp3lqpkq0q-source/lib/customisation.nix:268:17:
          267|     in commonAttrs // {
          268|       drvPath = assert condition; drv.drvPath;
             |                 ^
          269|       outPath = assert condition; drv.outPath;

       … in the left operand of the OR (||) operator
         at /nix/store/6s0m1qc31zw3l3kq0q4wd5cp3lqpkq0q-source/pkgs/development/interpreters/python/passthrufun.nix:28:45:
           27|         if lib.isDerivation value then
           28|           lib.extendDerivation (valid value || throw "${name} should use `buildPythonPackage` or `toPythonModule` if it is to be part of the Python packages set.") {} value
             |                                             ^
           29|         else

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: Package ‘python-2.7.18.7’ in /nix/store/6s0m1qc31zw3l3kq0q4wd5cp3lqpkq0q-source/pkgs/development/interpreters/python/cpython/2.7/default.nix:335 is marked as insecure, refusing to evaluate.
```

Errors emitted in nested structures (like e.g. when printing `nixpkgs`)
will still be printed in brackets.

Change-Id: I25aeddf08c017582718cb9772a677bf51b9fc2ad
This commit is contained in:
Rebecca Turner 2024-03-09 18:28:04 -08:00
parent 7e139c52dd
commit 9e7e927837
6 changed files with 120 additions and 62 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
doc/manual/rl-next/better-errors-in-nix-repl.md
View file

@ -1,6 +1,7 @@
---
synopsis: Concise error printing in `nix repl`
prs: 9928
cls: 811
---
Previously, if an element of a list or attribute set threw an error while

3
src/libcmd/repl.cc
View file

@ -167,7 +167,8 @@ struct NixRepl
.force = true,
.derivationPaths = true,
.maxDepth = maxDepth,
.prettyIndent = 2
.prettyIndent = 2,
.errors = ErrorPrintBehavior::ThrowTopLevel,
});
}
};

30
src/libexpr/print-options.hh
View file

@ -8,6 +8,29 @@
namespace nix {
/**
* How errors should be handled when printing values.
*/
enum class ErrorPrintBehavior {
/**
* Print the first line of the error in brackets: `«error: oh no!»`
*/
Print,
/**
* Throw the error to the code that attempted to print the value, instead
* of suppressing it it.
*/
Throw,
/**
* Only throw the error if encountered at the top level of the expression.
*
* This will cause expressions like `builtins.throw "uh oh!"` to throw
* errors, but will print attribute sets and other nested structures
* containing values that error (like `nixpkgs`) normally.
*/
ThrowTopLevel,
};
/**
* Options for printing Nix values.
*/
@ -68,6 +91,11 @@ struct PrintOptions
*/
size_t prettyIndent = 0;
/**
* How to handle errors encountered while printing values.
*/
ErrorPrintBehavior errors = ErrorPrintBehavior::Print;
/**
* True if pretty-printing is enabled.
*/
@ -86,7 +114,7 @@ static PrintOptions errorPrintOptions = PrintOptions {
.maxDepth = 10,
.maxAttrs = 10,
.maxListItems = 10,
.maxStringLength = 1024
.maxStringLength = 1024,
};
}

120
src/libexpr/print.cc
View file

@ -229,25 +229,21 @@ private:
void printDerivation(Value & v)
{
try {
Bindings::iterator i = v.attrs->find(state.sDrvPath);
NixStringContext context;
std::string storePath;
if (i != v.attrs->end())
storePath = state.store->printStorePath(state.coerceToStorePath(i->pos, *i->value, context, "while evaluating the drvPath of a derivation"));
Bindings::iterator i = v.attrs->find(state.sDrvPath);
NixStringContext context;
std::string storePath;
if (i != v.attrs->end())
storePath = state.store->printStorePath(state.coerceToStorePath(i->pos, *i->value, context, "while evaluating the drvPath of a derivation"));
if (options.ansiColors)
output << ANSI_GREEN;
output << "«derivation";
if (!storePath.empty()) {
output << " " << storePath;
}
output << "»";
if (options.ansiColors)
output << ANSI_NORMAL;
} catch (Error & e) {
printError_(e);
if (options.ansiColors)
output << ANSI_GREEN;
output << "«derivation";
if (!storePath.empty()) {
output << " " << storePath;
}
output << "»";
if (options.ansiColors)
output << ANSI_NORMAL;
}
bool shouldPrettyPrintAttrs(AttrVec & v)
@ -472,64 +468,68 @@ private:
output.flush();
checkInterrupt();
if (options.force) {
try {
try {
if (options.force) {
state.forceValue(v, v.determinePos(noPos));
} catch (Error & e) {
printError_(e);
return;
}
}
switch (v.type()) {
switch (v.type()) {
case nInt:
printInt(v);
break;
case nInt:
printInt(v);
break;
case nFloat:
printFloat(v);
break;
case nFloat:
printFloat(v);
break;
case nBool:
printBool(v);
break;
case nBool:
printBool(v);
break;
case nString:
printString(v);
break;
case nString:
printString(v);
break;
case nPath:
printPath(v);
break;
case nPath:
printPath(v);
break;
case nNull:
printNull();
break;
case nNull:
printNull();
break;
case nAttrs:
printAttrs(v, depth);
break;
case nAttrs:
printAttrs(v, depth);
break;
case nList:
printList(v, depth);
break;
case nList:
printList(v, depth);
break;
case nFunction:
printFunction(v);
break;
case nFunction:
printFunction(v);
break;
case nThunk:
printThunk(v);
break;
case nThunk:
printThunk(v);
break;
case nExternal:
printExternal(v);
break;
case nExternal:
printExternal(v);
break;
default:
printUnknown();
break;
default:
printUnknown();
break;
}
} catch (Error & e) {
if (options.errors == ErrorPrintBehavior::Throw
|| (options.errors == ErrorPrintBehavior::ThrowTopLevel
&& depth == 0)) {
throw;
}
printError_(e);
}
}

27
tests/functional/repl_characterization/data/errors.test Normal file
View file

@ -0,0 +1,27 @@
Errors at the top of an expression are printed normally:
nix-repl> builtins.throw "Evil puppy detected!!!"
error:
… while calling the 'throw' builtin
at «string»:1:1:
1| builtins.throw "Evil puppy detected!!!"
| ^
error: Evil puppy detected!!!
Errors in attribute values are printed inline, to make it easier to explore
values like nixpkgs where some parts of the value fail to evaluate:
nix-repl> { puppy = builtins.throw "This puppy is EVIL!!!"; puppy2 = "This puppy is GOOD :)"; }
{
puppy = «error: This puppy is EVIL!!!»;
puppy2 = "This puppy is GOOD :)";
}
Same for list values:
nix-repl> [ (builtins.throw "This puppy is EVIL!!!") ("This puppy is GOOD :)") ]
[
«error: This puppy is EVIL!!!»
"This puppy is GOOD :)"
]

1
tests/functional/repl_characterization/repl_characterization.cc
View file

@ -186,5 +186,6 @@ REPL_TEST(repl_overlays_destructure_without_formals_ok);
REPL_TEST(repl_overlays_error);
REPL_TEST(repl_printing);
REPL_TEST(stack_vars);
REPL_TEST(errors);
}; // namespace nix