Swift package manager unable to compile ncurses installed through Homebrew

Problem

The main problem are conflicts of the header files, since ncurses is also supplied in /Applications/Xcode.app/.../MacOSX10.14.sdk/usr/include.

A common pure C solution in such situations is to just specify the custom include and lib directories with -I repective -L and it would work, see my answer regarding C ncurses here: https://stackoverflow.com/a/56623033/2331445

This approach does not seem to work with the Swift package manager. But that doesn't mean it's not possible with a little effort.

Possible Solution

We need to make sure that the ncurses header files provided by the macOS SDK are ignored. We can do this by specifying the -Xcc -D__NCURSES_H parameter for the swift build command.

This works because in the header file, there is this typical:

#ifndef __NCURSES_H
#define __NCURSES_H
...
#endif

The problem, of course, is that our custom installation of ncurses using Brew is also affected. But we can work around it:

• copy the new ncurses header files into our Sources/Cncurses directory
• replace __NCURSES_H through something different, e.g. __CNCURSES_H (note leading 'C')
• then make sure that all further nested includes are first searched in our local include directory by replace the angle brackets of the includes with quotes, so e.g. instead of #include <ncursesw/unctrl.h> the form '#include "ncursesw/unctrl.h"' is used

This can actually be done with the following command line commands:

cd Sources/Cncurses
cp -r /usr/local/Cellar/ncurses/6.1/include include
find . -name '*.h' -exec sed -i ''  's/__NCURSES_H/__CNCURSES_H/g' {} \;
find . -name '*.h' -exec sed -i '' -E -e "s/<(.*(`find . -name '*.h' -exec basename {} \; |  paste -sd "|" -`))>/\"\1\"/g"  {} \;

The last statement may require some explanation. With the help of an echo command, you can look at the generated sed expression, i.e. if you execute

echo "s/<(.*(`find . -name '*.h' -exec basename {} \; |  paste -sd "|" -`))>/\"\1\"/g" 

you get the following output:

s/<(.*(termcap.h|form.h|term.h|panel.h|ncurses.h|termcap.h|cursesp.h|cursesf.h|etip.h|form.h|cursesw.h|nc_tparm.h|unctrl.h|cursesapp.h|term.h|cursslk.h|panel.h|ncurses.h|tic.h|eti.h|ncurses_dll.h|term_entry.h|menu.h|cursesm.h|curses.h|curses.h|cncurses.h))>/"\1"/g

As you can see, it searches and replaces only local available include files.

Test

For a test we need a simple ncurses example program. It should be built and we should make sure that the correct version of the library is used.

module.modulemap

My header file is called cncurses.h. The module.modulemap looks like this:

module cncurses [system] 
{
    umbrella header "cncurses.h"
    link "ncurses"
    export *
}

cncurses.h

cncurses.h is a one-liner, it imports our copied and customized ncurses.h file from our local include folder:

#include "include/ncurses.h"

main.swift

In the NcursesExample folder we have main.swift where we have a simple cncurses swift app:

import cncurses

initscr()
curs_set(0) 
move(5, 10)
addstr("NCURSES")
move(10, 10)
addstr("Hello World!")
refresh() 

select(0, nil, nil, nil, nil)

Package.swift

Please note here the pkgConfig: "ncurses" in the systemLibrary targets:

// swift-tools-version:5.0
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "NcursesExample",
    dependencies: [
    ],
    targets: [
        .systemLibrary(name: "cncurses", pkgConfig: "ncurses"),
        .target(name: "NcursesExample", dependencies: ["cncurses"]),
        .testTarget(
            name: "NcursesExampleTests",
            dependencies: ["NcursesExample"]),

    ]
)

Build

For pkg-config to do its job properly, we must first call the following:

export PKG_CONFIG_PATH="/usr/local/opt/ncurses/lib/pkgconfig"

Finally we initiate the build with:

swift build -Xcc -D__NCURSES_H 

So first we should test if the correct ncurses lib was used. We can do that with:

otool -L .build/x86_64-apple-macosx/debug/NcursesExample

Among other lines, the output contains this:

/usr/local/opt/ncurses/lib/libncursesw.6.dylib (compatibility version 6.0.0, current version 6.0.0)

which looks promising.

Finally calling the binary:

Xcode Project

If you want to generate a Xcode project, use the following command:

swift package generate-xcodeproj

Then load the project in Xcode and

• select the project node
• in Build settings enter Preprocessor in the search field in the upper right
• under Apple Clang - Preprocessing / Preprocess Macros add __NCURSES_H=1 for Debug and Release