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libexpr: Support structured error classes

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While preparing PRs like #9753, I've had to change error messages in
dozens of code paths. It would be nice if instead of

    EvalError("expected 'boolean' but found '%1%'", showType(v))

we could write

    TypeError(v, "boolean")

or similar. Then, changing the error message could be a mechanical
refactor with the compiler pointing out places the constructor needs to
be changed, rather than the error-prone process of grepping through the
codebase. Structured errors would also help prevent the "same" error
from having multiple slightly different messages, and could be a first
step towards error codes / an error index.

This PR reworks the exception infrastructure in `libexpr` to
support exception types with different constructor signatures than
`BaseError`. Actually refactoring the exceptions to use structured data
will come in a future PR (this one is big enough already, as it has to
touch every exception in `libexpr`).

The core design is in `eval-error.hh`. Generally, errors like this:

    state.error("'%s' is not a string", getAttrPathStr())
      .debugThrow<TypeError>()

are transformed like this:

    state.error<TypeError>("'%s' is not a string", getAttrPathStr())
      .debugThrow()

The type annotation has moved from `ErrorBuilder::debugThrow` to
`EvalState::error`.
This commit is contained in:
Rebecca Turner 2024-01-22 17:08:29 -08:00
parent c62c21e29a
commit c6a89c1a16
No known key found for this signature in database
40 changed files with 653 additions and 545 deletions
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30
src/libexpr/eval-cache.cc
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@ -491,7 +491,7 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErro
if (forceErrors)
debug("reevaluating failed cached attribute '%s'", getAttrPathStr(name));
else
throw CachedEvalError("cached failure of attribute '%s'", getAttrPathStr(name));
throw CachedEvalError(root->state, "cached failure of attribute '%s'", getAttrPathStr(name));
} else
return std::make_shared<AttrCursor>(root,
std::make_pair(shared_from_this(), name), nullptr, std::move(attr));
@ -500,7 +500,7 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErro
// evaluate to see whether 'name' exists
} else
return nullptr;
//throw TypeError("'%s' is not an attribute set", getAttrPathStr());
//error<TypeError>("'%s' is not an attribute set", getAttrPathStr()).debugThrow();
}
}
@ -508,7 +508,7 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErro
if (v.type() != nAttrs)
return nullptr;
//throw TypeError("'%s' is not an attribute set", getAttrPathStr());
//error<TypeError>("'%s' is not an attribute set", getAttrPathStr()).debugThrow();
auto attr = v.attrs->get(name);
@ -574,14 +574,14 @@ std::string AttrCursor::getString()
debug("using cached string attribute '%s'", getAttrPathStr());
return s->first;
} else
root->state.error("'%s' is not a string", getAttrPathStr()).debugThrow<TypeError>();
root->state.error<TypeError>("'%s' is not a string", getAttrPathStr()).debugThrow();
}
}
auto & v = forceValue();
if (v.type() != nString && v.type() != nPath)
root->state.error("'%s' is not a string but %s", getAttrPathStr()).debugThrow<TypeError>();
root->state.error<TypeError>("'%s' is not a string but %s", getAttrPathStr()).debugThrow();
return v.type() == nString ? v.c_str() : v.path().to_string();
}
@ -616,7 +616,7 @@ string_t AttrCursor::getStringWithContext()
return *s;
}
} else
root->state.error("'%s' is not a string", getAttrPathStr()).debugThrow<TypeError>();
root->state.error<TypeError>("'%s' is not a string", getAttrPathStr()).debugThrow();
}
}
@ -630,7 +630,7 @@ string_t AttrCursor::getStringWithContext()
else if (v.type() == nPath)
return {v.path().to_string(), {}};
else
root->state.error("'%s' is not a string but %s", getAttrPathStr()).debugThrow<TypeError>();
root->state.error<TypeError>("'%s' is not a string but %s", getAttrPathStr()).debugThrow();
}
bool AttrCursor::getBool()
@ -643,14 +643,14 @@ bool AttrCursor::getBool()
debug("using cached Boolean attribute '%s'", getAttrPathStr());
return *b;
} else
root->state.error("'%s' is not a Boolean", getAttrPathStr()).debugThrow<TypeError>();
root->state.error<TypeError>("'%s' is not a Boolean", getAttrPathStr()).debugThrow();
}
}
auto & v = forceValue();
if (v.type() != nBool)
root->state.error("'%s' is not a Boolean", getAttrPathStr()).debugThrow<TypeError>();
root->state.error<TypeError>("'%s' is not a Boolean", getAttrPathStr()).debugThrow();
return v.boolean;
}
@ -665,14 +665,14 @@ NixInt AttrCursor::getInt()
debug("using cached integer attribute '%s'", getAttrPathStr());
return i->x;
} else
throw TypeError("'%s' is not an integer", getAttrPathStr());
root->state.error<TypeError>("'%s' is not an integer", getAttrPathStr()).debugThrow();
}
}
auto & v = forceValue();
if (v.type() != nInt)
throw TypeError("'%s' is not an integer", getAttrPathStr());
root->state.error<TypeError>("'%s' is not an integer", getAttrPathStr()).debugThrow();
return v.integer;
}
@ -687,7 +687,7 @@ std::vector<std::string> AttrCursor::getListOfStrings()
debug("using cached list of strings attribute '%s'", getAttrPathStr());
return *l;
} else
throw TypeError("'%s' is not a list of strings", getAttrPathStr());
root->state.error<TypeError>("'%s' is not a list of strings", getAttrPathStr()).debugThrow();
}
}
@ -697,7 +697,7 @@ std::vector<std::string> AttrCursor::getListOfStrings()
root->state.forceValue(v, noPos);
if (v.type() != nList)
throw TypeError("'%s' is not a list", getAttrPathStr());
root->state.error<TypeError>("'%s' is not a list", getAttrPathStr()).debugThrow();
std::vector<std::string> res;
@ -720,14 +720,14 @@ std::vector<Symbol> AttrCursor::getAttrs()
debug("using cached attrset attribute '%s'", getAttrPathStr());
return *attrs;
} else
root->state.error("'%s' is not an attribute set", getAttrPathStr()).debugThrow<TypeError>();
root->state.error<TypeError>("'%s' is not an attribute set", getAttrPathStr()).debugThrow();
}
}
auto & v = forceValue();
if (v.type() != nAttrs)
root->state.error("'%s' is not an attribute set", getAttrPathStr()).debugThrow<TypeError>();
root->state.error<TypeError>("'%s' is not an attribute set", getAttrPathStr()).debugThrow();
std::vector<Symbol> attrs;
for (auto & attr : *getValue().attrs)