Hi Dlang forums.
I ran into some problems when trying to cross compile. Hope this
clarifies the set-up for anyone with the same problems.
Additionally, perhaps these more explicit instructions / pitfalls
could be put into the official [wiki page about cross
compiling](https://wiki.dlang.org/Cross-compiling_with_LDC). As a
new user, this would have helped greatly.
# Guide
## Step 1: Obtain an LDC distribution compiled for the target
Prebuilt LDC binaries are found on the [LDC GitHub repo's
releases page](https://github.com/ldc-developers/ldc/releases/)
For a 64-bit windows target, download
`ldc2-<version>-windows-x64.7z`. (note that you may need to click
"see all releases", as some may be hidden by default).
Extract this archive.
Find the "lib" folder in the archive, then rename and move it to
a system-wide location. The wiki page recommends
`%%ldcbinarypath%%/../lib-win64`, which on my system is
equivalent to `/usr/lib-win64`
## Step 2: Tweak the LDC Configuration file
As per [Cross Compiling with
LDC](https://wiki.dlang.org/Cross-compiling_with_LDC), add your
target "triple" name to the `ldc2.conf` file, putting the path to
your target's "lib file" (the one that we extracted and moved in
step 1) inside `lib-dirs = [ ... ]`.
From my personal testing, lib-dirs allows absolute and relative
paths.
### Pitfall 1: Using the "wrong" LDC configuration file
Before tweaking the system-wide configuration in
`/etc/ldc2.conf`, I wanted to test one out in the current working
directory of my project, which according to [Using
LDC](https://wiki.dlang.org/Using_LDC), is one of valid places
that LDC will find a configuration file. I incorrectly assumed,
however, that ldc2 will read both the local and system-wide
config files.
So, I copied the the "Win64" configuration snippet from [Cross
Compiling with
LDC](https://wiki.dlang.org/Cross-compiling_with_LDC) into a
local `ldc2.conf` (into my project's root), and ran `ldc2
-mtriple=x86_64-windows-msvc source/app.d`, but received an error
```
Error: `object` not found. object.d may be incorrectly installed
or corrupt.
ldc2 might not be correctly installed.
Please check your ldc2.conf configuration file.
Installation instructions can be found at
http://wiki.dlang.org/LDC.
```
This happens because unlike our local configuration file, the
system wide one (at `/etc/ldc2.conf`) contains a line that tells
ldc2 where to find necessary files.
```
default:
{
// ...
post-switches = [
"-I/usr/include/dlang/ldc",
];
// ...
}
```
#### Solution 1: Use the system-wide ldc2.conf only
Copy your configuration to the system-wide `/etc/ldc2.conf`, then
**delete the `ldc2.conf` inside the poject directory**
#### Solution 2: Add post-switches to the local config
Add the following lines to your local `ldc2.conf`, under
`switches`. replace `-I/usr/include/dlang/ldc` with a different
ldc includes path if necessary.
```
post-switches = [
"-I/usr/include/dlang/ldc",
];
```
### Pitfall 2: Incorrect "lib-dirs" option
If you left your `lib-dirs` path as
`"%%ldcbinarypath%%/../lib-aarch64"`, it may be incorrect.
This value must reflect the location of the "lib" folder that we
extracted and moved in step 1.
## Step 3: Verify cross compilation is working
Compile a Dlang file for your target using ldc2. In my case, the
command was `ldc2 -mtriple=x86_64-windows-msvc source/app.d`
If everything is set up correctly, congratulations! We now know
how to cross compile with Dlang.
