Hi,

I'm facing this error and I'm not sure why. For context, I'm trying to build a parser for simple mathematical expressions given as strings i.e. "1 + 2". My main experience is in Python and I wanted to explore the D language so I thought of doing this small project as an exercise. The source code is here.

NOTE: The error is happening when I'm using the SumType and I suspect that I'm using it incorrectly.

The error can be seen below:

❯ dub run --vverbose --config=executable
Using dub registry url 'https://code.dlang.org/'
'git --git-dir=/home/guacs/projects/meval/.git describe --long --tags' failed with exit code 128: fatal: No names found, cannot describe anything.
Determined package version using GIT: meval ~main
Collecting dependencies for meval
Scanning local packages...
iterating dir /home/guacs/.dub/packages/
iterating dir /home/guacs/.dub/packages/ entry libddoc-0.8.0
iterating dir /home/guacs/.dub/packages/ entry emsi_containers-0.9.0
iterating dir /home/guacs/.dub/packages/ entry libdparse-0.22.0
iterating dir /home/guacs/.dub/packages/ entry inifiled-1.3.3
iterating dir /home/guacs/.dub/packages/ entry silly-1.1.1
iterating dir /home/guacs/.dub/packages/ entry dunit-1.0.16
iterating dir /home/guacs/.dub/packages/ entry dcd-0.15.2
iterating dir /home/guacs/.dub/packages/ entry dscanner-0.14.0
  Found dependency silly 1.1.1
  Collecting dependencies for silly
Add config silly library
Add config meval unittest
Including meval unittest -> silly library
Add config meval executable
Including meval executable -> silly library
NON-PRIMARY: meval executable
Eliminating config executable for meval
    meval unittest -> silly library
Using configuration 'library' for silly
Using configuration 'unittest' for meval
Generating using build
Creating build generator.
Add config meval executable
Add config silly library
Add config meval unittest
Including meval unittest -> silly library
Including meval executable -> silly library
NON-PRIMARY: meval unittest
Eliminating config unittest for meval
    meval executable -> silly library
Using configuration 'executable' for meval
Using configuration 'library' for silly
Configuring target meval (executable /home/guacs/projects/meval meval)
deps: meval -> "silly"
  Configuring target without output silly
deps: silly ->
Configure dependencies of meval, deps:
Configuring dependent meval, deps:
    Starting Performing "debug" build using /home/guacs/dlang/dmd-2.102.1/linux/bin64/dmd for x86_64.
Target '/home/guacs/.dub/cache/meval/~main/build/executable-debug-linux.posix-x86_64-dmd_v2.102.1-BA8BA57C46223F272147C400395CD614568C52989F3A410949BE6AC73D142207/meval' doesn't exist, need rebuild.
    Building meval ~main: building configuration [executable]
[cwd=/home/guacs/projects/meval] /home/guacs/dlang/dmd-2.102.1/linux/bin64/dmd -c -of../../.dub/cache/meval/~main/build/executable-debug-linux.posix-x86_64-dmd_v2.102.1-BA8BA57C46223F272147C400395CD614568C52989F3A410949BE6AC73D142207/meval.o -debug -g -w -version=Have_meval -version=Have_silly -Isource/ -I../../.dub/packages/silly-1.1.1/silly source/app.d source/enums.d source/evaluator.d source/exceptions.d source/expr.d source/parser.d source/tokenizer.d source/utils.d ../../.dub/packages/silly-1.1.1/silly/silly.d -vcolumns
Error: unknown, please file report on issues.dlang.org
FAIL ../../.dub/cache/meval/~main/build/executable-debug-linux.posix-x86_64-dmd_v2.102.1-BA8BA57C46223F272147C400395CD614568C52989F3A410949BE6AC73D142207 meval executable
Error /home/guacs/dlang/dmd-2.102.1/linux/bin64/dmd failed with exit code 1.
Full exception: dub.compilers.compiler.CompilerInvocationException@source/dub/compilers/compiler.d(170): /home/guacs/dlang/dmd-2.102.1/linux/bin64/dmd failed with exit code 1.
----------------
??:? [0x5632bfdc21e6]
??:? [0x5632bfdc3cf6]
??:? [0x5632bfda4cef]
??:? [0x5632bfca798a]
??:? [0x5632bfc526ea]
??:? [0x5632bfc58b5a]
??:? [0x5632bfc2eefa]
??:? [0x5632bfc2cb79]
??:? [0x5632bfc2980f]
??:? [0x5632bfc28e41]
??:? [0x5632bfc27e05]
??:? [0x5632bfa5e1a4]
??:? [0x5632bfd3fcd2]
??:? [0x5632bfd40a3d]
??:? [0x5632bfd38b06]
??:? [0x5632bfda49db]
??:? [0x5632bfda48d5]
??:? [0x5632bfda472d]
??:? __libc_start_main [0x7f3bec33f082]
??:? [0x5632bfa25c49]

Compiler/DUB details:

❯ dub --version
DUB version 1.31.1, built on Feb 15 2023

❯ dmd --version
DMD64 D Compiler v2.102.1
Copyright (C) 1999-2023 by The D Language Foundation, All Rights Reserved written by Walter Bright

Also, I'm using WSL2 on Windows 10 and the Linux version is: Ubuntu 20.04.5 LTS

On Sunday, 26 February 2023 at 02:33:21 UTC, guacs wrote:

I am not sure whether this is the specific error that is causing your problem, but there is a mistake in your use of SumType in expr.d. [1]

On line 10, you declare

alias Expression = SumType!(Number, Binary, Unary, Group);

Later, you declare Binary and Unary like this:

struct Binary {
    Expression leftOperand;
    Expression rightOperand;
    Token operator;

    // etc.
}

struct Unary {
    Expression operand;
    Token operator;

    // etc.
}

Since Expression contains Binary and Unary, and Binary and Unary contain Expression, that means Expression contains itself--which is not allowed, because it would result in Expression.sizeof being infinite.

The fix is to change Binary and Unary so that they contain pointers to Expression, like this:

struct Binary {
    Expression* leftOperand;  // pointer
    Expression* rightOperand; // pointer
    Token operator;

    // etc.
}

struct Unary {
    Expression* operand; // pointer
    Token operator;

    // etc.
}

[1] https://github.com/VisakhChekur/meval/blob/error/source/expr.d

On Sunday, 26 February 2023 at 07:11:55 UTC, Paul Backus wrote:

It should display the proper error message then

On Sunday, 26 February 2023 at 14:17:50 UTC, ryuukk_ wrote:

Example of error message for this particular error with zig:

An error occurred:
/tmp/playground921468696/play.zig:4:20: error: union 'play.Expression' depends on itself
const Expression = union(enum) {
                   ^~~~~
/tmp/playground921468696/play.zig:23:5: note: while checking this field
    expr: Expression
    ^~~~~~~~~~~~~~~~
/tmp/playground921468696/play.zig:8:5: note: while checking this field
    group: Group,
    ^~~~~~~~~~~~
referenced by:
    callMain: /usr/local/bin/lib/std/start.zig:604:17
    initEventLoopAndCallMain: /usr/local/bin/lib/std/start.zig:548:51
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

I don't particularly enjoy zig, but they tell us how errors should be reported to the users, they do it very nicely

On Sunday, 26 February 2023 at 14:17:50 UTC, ryuukk_ wrote:

Normally when you do this you will get a proper error message. For example, attempting to compile the following program:

import std.sumtype;

alias Test = SumType!S;

struct S
{
    Test st;
}

...will give you this error message:

/usr/include/dmd/phobos/std/sumtype.d(309): Error: union `std.sumtype.SumType!(S).SumType.Storage` no size because of forward reference
forum.d(3): Error: template instance `std.sumtype.SumType!(S)` error instantiating

I'm not sure why OP didn't get a proper error message. It's possible that there's some other issue with their code that stops the error message from being printed. I did not attempt to reproduce their error myself.