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Error Rewriting

When running Erde code directly (either via erde.load or the CLI), runtime errors will report line numbers and file names for the compiled Lua code:

myfile.erde
print('a' + 1)
stdout
[string "erde::1::test.erde"]:3: attempt to add a 'string' with a 'number'
stack traceback:
    [C]: in metamethod 'add'
    [string "erde::1::test.erde"]:3: in main chunk
    (...tail calls...)
    [C]: in ?

In order to report references back to the original Erde file, we need to rewrite the error. Erde originally tried to handle error rewriting automatically, but this has many shortcomings:

  1. It's not clear whether to use erde.rewrite or erde.traceback, as the former is more suitable for errors meant to be caught, but the latter is more suitable if the error is allowed to propogate.
  2. Errors may be rewritten multiple times, causing misleading stacktraces.
  3. Throwing rewritten errors affects users wanting to use xpcall themselves, since the stack will only "unwind" from the point that the error was rethrown, rather than from the point of the original error.
  4. It's very difficult to handle the case where an error-prone function is declared in Erde, but called in Lua.

There were multiple attempts to overcome these, but every solution had major flaws. Thus, to keep things simple and transparent, error rewriting is delegated to the user.

IMPORTANT

Erde leaves it up to the user to properly handle error rewriting.

Users will generally want to use xpcall with erde.rewrite or erde.traceback at the top level they wish to rewrite errors. For example:

init.lua
local erde = require('erde')
erde.load()

local ok, result = xpcall(function()
  require('my_erde_entry')
end, erde.rewrite)

if not ok then
  error(result)
end
info

If you are using the CLI (erde run), you probably do not need to manually handle error rewriting. See below.

Package Loader Error Rewriting​

When using the Erde package loader (erde.load), Lua's native debug.traceback function will be replaced with erde.traceback, a wrapper that handles error rewriting.

However, this only handles cases where debug.traceback would be called. For example, if a user explicitly calls error('my error'), the error will not be rewritten.

CLI Error Rewriting​

When running Erde files directly from the CLI (erde run xxx.erde), any top level errors will be rewritten before printing to stdout. Additionally, since erde run calls erde.load internally, debug.traceback will also be overridden.