error: assignment of read-only variable ‘const_a’

[stefanos82]

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---

Bug description

A clear and concise description of the bug you are experiencing.
Tell what you were trying to do and what happened instead.

The latest commit f448b29 breaks the code below.

$ nelua const.nelua 
C compilation for 'nelua_cache/const' failed:
nelua_cache/const.c: In function ‘nelua_main’:
nelua_cache/const.c:53:11: error: assignment of read-only variable ‘const_a’
   53 |   const_a = const_x;
      |           ^

Code example

Provide minimal reproduction code to test the bug.
Please, format the code properly and try to keep it as simple as possible, just focusing on the experienced bug.

local x <const> = 1
local a <const> = x
print(a) -- outputs: 1

-- uncommenting the following will trigger the compile error:
-- error: cannot assign a constant variable
-- a = 2

Expected behavior

A clear and concise description of what you expected to happen.

To see 1 as output

Environment

Provide relevant information about your environment:

• Nelua version (you can check with nelua -v).

Nelua 0.2.0-dev
Build number: 1155
Git date: 2021-07-15 17:28:09 -0300
Git hash: f448b29674a399600d4f1b19cd74b273233b5b36
Copyright (C) 2019-2021 Eduardo Bart (https://nelua.io/)

• Platform (e.g. Windows/MSYS2, Ubuntu Linux, MacOS)

OS: GNU / Linux Debian testing 64-bit

• C compiler if your bug has C compiler errors. (e.g. GCC 10.2, Clang 11)

gcc version 10.2.1 20210110 (Debian 10.2.1-6) 

[edubart]

Thanks for reporting! I've just fixed. In recent commits I've started to emit more const keyword in the C code generator and this happened. I've added your example to the test suite, so this regression should not happen again.

[stefanos82]

So local a <const> = x is not a const in C? 🤔

This is what I mean

[stefanos82]

lol forget what I wrote above; in my mind I saw them in reverse order 🤦

[edubart]

So local a <const> = x is not a const in C?

The <const> annotation is there to check at compile time for variable mutation (like in Lua), <const> in Nelua does not necessarily mean that the variable will be const in C. But some consts in Nelua depending on its semantics it will be const in C, note that this is usually not a problem because in C const does not impact performance, I've just added const in C code generator to suppress some warnings when dealing with const pointers, as side effect some integers are marked as const too and this is harmless, unless triggers a C compile error (this issue).

[stefanos82]

But some consts in Nelua depending on its semantics it will be const in C, note that this is usually not a problem because in C const does not impact performance, I've just added const in C code generator to suppress some warnings when dealing with const pointers, as side effect some integers are marked as const too and this is harmless, unless triggers a C compile error (this issue).

Ah OK, I see.