commit ee99452158de5e2fa804bd10de7669848f3b3952
parent 127a8e80fe0d74efd26994b3877cdc77b712ea56
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Fri, 28 Feb 2025 14:53:31 -0300
Error object cannot be nil
Lua will change a nil as error object to a string message, so that it
never reports an error with nil as the error object.
Diffstat:
4 files changed, 23 insertions(+), 8 deletions(-)
diff --git a/ldebug.c b/ldebug.c
@@ -844,7 +844,9 @@ l_noret luaG_runerror (lua_State *L, const char *fmt, ...) {
va_start(argp, fmt);
msg = luaO_pushvfstring(L, fmt, argp); /* format message */
va_end(argp);
- if (msg != NULL && isLua(ci)) { /* Lua function? (and no error) */
+ if (msg == NULL) /* no memory to format message? */
+ luaD_throw(L, LUA_ERRMEM);
+ else if (isLua(ci)) { /* Lua function? */
/* add source:line information */
luaG_addinfo(L, msg, ci_func(ci)->p->source, getcurrentline(ci));
setobjs2s(L, L->top.p - 2, L->top.p - 1); /* remove 'msg' */
diff --git a/ldo.c b/ldo.c
@@ -112,12 +112,16 @@ void luaD_seterrorobj (lua_State *L, TStatus errcode, StkId oldtop) {
break;
}
default: {
- lua_assert(errorstatus(errcode)); /* real error */
- setobjs2s(L, oldtop, L->top.p - 1); /* error message on current top */
+ lua_assert(errorstatus(errcode)); /* must be a real error */
+ if (!ttisnil(s2v(L->top.p - 1))) { /* error object is not nil? */
+ setobjs2s(L, oldtop, L->top.p - 1); /* move it to 'oldtop' */
+ }
+ else /* change it to a proper message */
+ setsvalue2s(L, oldtop, luaS_newliteral(L, "<error object is nil>"));
break;
}
}
- L->top.p = oldtop + 1;
+ L->top.p = oldtop + 1; /* top goes back to old top plus error object */
}
diff --git a/manual/manual.of b/manual/manual.of
@@ -290,7 +290,9 @@ an @def{error object}
is propagated with information about the error.
Lua itself only generates errors whose error object is a string,
but programs can generate errors with
-any value as the error object.
+any value as the error object,
+except @nil.
+(Lua will change a @nil as error object to a string message.)
It is up to the Lua program or its host to handle such error objects.
For historical reasons,
an error object is often called an @def{error message},
@@ -8082,6 +8084,8 @@ multiple assignment:
The default for @id{a2} is @id{a1}.
The destination range can overlap with the source range.
The number of elements to be moved must fit in a Lua integer.
+If @id{f} is larger than @id{e},
+nothing is moved.
Returns the destination table @id{a2}.
@@ -9402,6 +9406,11 @@ declare a local variable with the same name in the loop body.
A chain of @id{__call} metamethods can have at most 15 objects.
}
+@item{
+In an error, a @nil as the error object is replaced by a
+string message.
+}
+
}
}
diff --git a/testes/errors.lua b/testes/errors.lua
@@ -46,7 +46,7 @@ end
assert(doit("error('hi', 0)") == 'hi')
-- test nil error message
-assert(doit("error()") == nil)
+assert(doit("error()") == "<error object is nil>")
-- test common errors/errors that crashed in the past
@@ -614,7 +614,7 @@ do
assert(not res and msg == t)
res, msg = pcall(function () error(nil) end)
- assert(not res and msg == nil)
+ assert(not res and msg == "<error object is nil>")
local function f() error{msg='x'} end
res, msg = xpcall(f, function (r) return {msg=r.msg..'y'} end)
@@ -634,7 +634,7 @@ do
assert(not res and msg == t)
res, msg = pcall(assert, nil, nil)
- assert(not res and msg == nil)
+ assert(not res and type(msg) == "string")
-- 'assert' without arguments
res, msg = pcall(assert)