mercury/Documentation/README.MSYS2.md

Mercury on MSYS2

This file documents the port of Mercury to Windows using the environments provided by the MSYS2 platform.

Note that MSYS2 is separate from the older MSYS / MinGW project. That older project is no longer maintained, and we do not recommend its use with Mercury.

Contents

• Overview
• MSYS2 environments
• Prerequisites
• Installing in the MSYS environment
• Installing in the UCRT64, MINGW64, MINGW32 or CLANG64 environments
• Installing the java grade in MSYS2
• Installing the csharp grade in MSYS2
• Using Mercury in the MSYS2 shell
• Using Mercury in the Windows Command Prompt
• Missing libwinpthread-1.dll

Overview

MSYS2 is a POSIX-like native build environment for Windows. It provides a package manager, and tools like bash, make and gcc (via the MinGW-w64 port).

You can use MSYS2 to build a native Windows Mercury compiler. This compiler generates executables that run on Windows directly. These executables do not need MSYS2 or Cygwin to run.

Alternatively, you can use the MSYS2 environment to install a Mercury compiler using the Cygwin port of GCC. This compiler only runs in the MSYS2 shell, but provides an experience closer to that on Unix-like systems.

Finally, you can use the MSYS2 environment to install a Mercury compiler using MSVC. See README.MS-VisualC.md for further details.

This document assumes you installed MSYS2 in C:\msys64. If you installed MSYS2 in a different directory, then use your specific installation path in the examples below.

MSYS2 Environments

An MSYS2 environment controls what architecture, C compiler, linker and system libraries are used. Further details can be found on the Environments page of the MSYS2 website.

To help you choose an MSYS2 environment, we list the properties of each environment that are relevant to Mercury in the following table.

MSYS2 Env.	64-bit?	C Compiler	C Runtime	Usage
MSYS	Yes	GCC/Clang (Cygwin)	msys-2.0.dll	Shell only
UCRT64	Yes	GCC (MinGW-w64)	UCRT	Shell, CMD, PS
MINGW64	Yes	GCC (MinGW-w64)	MSVCRT	Shell, CMD, PS
MINGW32	No	GCC (MinGW-w64)	MSVCRT	Shell, CMD, PS
CLANG64	Yes	Clang (MinGW-w64)	UCRT	Shell, CMD, PS

The MSYS2 Env. column contains the names of MSYS2 environments. These names correspond to the names of the launchers in the Windows Start Menu. For example, the launcher for the MSYS environment is named MSYS2 MSYS.

The 64-bit? column specifies whether 64-bit code is generated in the MSYS2 environment. If the entry is "No", then 32-bit code is generated.

The C Compiler column says which C compilers are available in the environment.

The C Runtime column says what C runtime library is used. The possible runtimes are:

• msys-2.0.dll - the MSYS2 runtime library.
• UCRT - the Universal C Runtime.
• MSVCRT - the Microsoft Visual C Runtime.

If you want to install a Mercury compiler that creates native Windows executables, then you must choose an environment that uses the UCRT or MSVCRT.

The Usage column says which environments you can use the Mercury compiler and executables generated by it in. The possible environments are:

• Shell - the MSYS2 shell.
• CMD - the Windows Command Prompt (cmd.exe).
• PS - PowerShell.

If you want to install a Mercury compiler that creates native 64-bit Windows executables, then we recommend using the UCRT64 environment. We do not recommend using the MINGW64 environment unless your code requires the MSVCRT (e.g. because it contains foreign code that depends on it). You should also note that the MSYS2 project considers the MINGW32 environment to be a legacy environment.

Aside from the above, there is also a CLANGARM64 MSYS2 environment. We have not tested Mercury in this environment. It may or may not work. Users who attempt to use the CLANGARM64 environment are encouraged to report their results.

Prerequisites

This section describes the packages that need to be installed in MSYS2 to build Mercury. Packages can be installed from the MSYS2 shell using the pacman package manager. See MSYS2 Package Management for further details.

Required Packages

For all choices of MSYS2 environment, the following packages must be installed in order to build Mercury:

• tar
• gzip (if you have the .tar.gz download)
• xz (if you have the .tar.xz download)
• make
• binutils
• diffutils

To install these packages do:

pacman -S tar gzip xz make binutils diffutils

C Compiler Toolchain Packages

Each MSYS2 environment has its own C compiler toolchain. You must install the correct package for your selected environment.

For the MSYS environment, the GCC package is gcc and the Clang package is clang. You can install GCC by doing:

pacman -S gcc

or:

pacman -S clang

For the UCRT64 environment, the GCC package is mingw-w64-ucrt64-x86_64-gcc. You can install it by doing:

pacman -S mingw-w64-ucrt64-x86_64-gcc

For the MINGW64 environment, the GCC package is mingw-w64-x86_64-gcc. You can install it by doing:

pacman -S mingw-w64-x86_64-gcc

For the MINGW32 environment, the GCC package is mingw-w64-i686-gcc. You can install it by doing:

pacman -S mingw-w64-i686-gcc

For the CLANG64 environment, the Clang package is mingw-w64-clang-x86_64-clang. You can install it by doing:

pacman -S mingw-w64-clang-x86_64-clang

Note that because of how MSYS2 environments manage the PATH variable, you might have multiple versions of gcc or clang in your PATH. In particular, the bin directory used by the MSYS environment is included in the PATH of all other MSYS2 environments. A common problem is accidentally using the MSYS compilers. This happens if you forgot to install the compiler package for your specific environment (e.g. UCRT64).

Documentation Packages

To build the Mercury documentation, you need the following packages:

• texinfo
• lynx (to convert HTML to plain text)

To install these packages do:

pacman -S texinfo lynx

Bootstrap Packages

To build Mercury directly from git, you also need the following packages:

• m4
• autoconf
• flex
• bison

To install these packages do:

pacman -S m4 autoconf flex bison

Building Mercury directly from git requires that you have an already installed Mercury compiler in the MSYS2 PATH to bootstrap from. You can obtain a bootstrap compiler by installing the source distribution using the standard instructions in this file. Aside from that, the other details are similar to what is described in this file.

See INSTALL.git and README.bootstrap for general advice on building Mercury from a git clone.

Installing in the MSYS environment

To install the Mercury source distribution in the MSYS2 MSYS environment, follow these steps:

1. Ensure that you are actually in the MSYS environment. For example, check that the value of the MSYSTEM environment variable is MSYS.

2. If you want to install the java grade, see below.

3. If you want to install the csharp grade, see below.

4. Unpack the Mercury source distribution:

    tar -xzf mercury-srcdist-VERSION.tar.gz
   

   or:

    tar -xJf mercury-srcdist-VERSION.tar.xz
   

   VERSION is the Mercury version number like 22.01 or rotd-2025-12-27.

5. Change into the Mercury source directory and run the configure script:

    ./configure --prefix=/mercury
   

   The --prefix option specifies the installation prefix. Its argument is the directory that Mercury will be installed into. In the MSYS2 MSYS environment, the value of the --prefix option must be a Unix-style path that uses forward slash, /, as the path separator. The value of the --prefix option must not be a Windows-style path beginning with a drive letter and colon (:) or use backslash (\), as a path separator.

   Correct installation prefix:

   ./configure --prefix=/c/mercury
   

   Incorrect installation prefixes:

   ./configure --prefix="C:/mercury" (Drive letter)
   ./configure --prefix=\c\mercury   (Backslash instead of forward slash)
   

   Note that the installation prefix used in the MSYS environment has a different form to the one used in the other MSYS2 environments.

   If you want to use clang as a C compiler instead of gcc, then pass the option --with-cc=clang to configure. For example:

   ./configure --prefix=/mercury --with-cc=clang
   

   Other options to the configure script behave as normal.

6. Run make and then make install. You can do a parallel build and install by doing make PARALLEL=-jN and make PARALLEL=-jN install, where N is the number of jobs to do in parallel.

Installing in the UCRT64, MINGW64, MINGW32 or CLANG64 environments

To install the Mercury source distribution in any of the MSYS2 UCRT64, MINGW64, MINGW32, CLANG64 environments, follow these steps:

1. Ensure that you are actually in the desired environment. For example, check that the value of the MSYSTEM environment variable is UCRT64, MINGW64, MINGW32 or CLANG64 as appropriate.

2. If you want to install the java grade, see below.

3. If you want to install the csharp grade, see below.

4. Unpack the Mercury source distribution:

   tar -xzf mercury-srcdist-VERSION.tar.gz
   

   or:

   tar -xJf mercury-srcdist-VERSION.tar.xz
   

   VERSION is the Mercury version number like 22.01 or rotd-2025-12-27.

5. Change into the Mercury source directory and run the configure script:

    ./configure --prefix="C:/mercury"
   

   The --prefix option specifies the installation prefix. Its argument is the directory that Mercury will be installed into (here C:/mercury). In the MSYS2 UCRT64, MINGW64, MINGW32 and CLANG64 environments, the value of the --prefix option must be a full Windows path beginning with a drive letter and colon (:). You must use forward slash (/) as the path separator, not backslash (\).

   Do NOT set the installation prefix to be a Unix-style path. That will not work because the MSYS2 shell and the generated executables each interpret it differently. Specifically, MSYS2 does path translation for Unix-style paths, whereas generated executables do not.

   Correct installation prefix:

   ./configure --prefix="C:/mercury" (Drive letter and forward slash)
   

   Incorrect installation prefixes:

   ./configure --prefix="C:\mercury" (Backslash instead of forward slash)
   ./configure --prefix=/c/mercury   (Unix-style path)
   

   Getting the form of the argument to the --prefix option wrong is the most common mistake made when installing Mercury in the MSYS2 environments. It will result in a Mercury installation that will not work.

   Note that the installation prefix used in the MSYS environment has a different form to the one used in the MSYS2 environments covered in this section.

   If you are using the CLANG64 environment, then add --with-cc=clang to the configure command to tell it that you want to use clang as the C compiler to build Mercury.

   ./configure --prefix="C:/mercury" --with-cc=clang
   

   Other options to the configure script behave as they do on other systems.

6. Run make and then make install. You can do a parallel build and install by doing make PARALLEL=-jN and make PARALLEL=-jN install, where N is the number of jobs to do in parallel.

Installing the java grade in MSYS2

To build and install the java grade with MSYS2, you require a Windows version of the JDK to be installed on your system. The following tools must be present in the MSYS2 PATH:

• The Java compiler (javac).
• The Java archive tool (jar).
• The Java runtime (java).

To add them to the MSYS2 PATH, do the following:

export PATH="/c/Program\ Files/Java/jdk-21/bin":$PATH

The details will vary depending on which distribution and version of Java you are using.

You can persist the above PATH changes across sessions by adding the above line to your ~/.bash_profile.

See README.Java.md for further details.

Installing the csharp grade in MSYS2

To build and install the csharp grade with MSYS2, you will require the Visual C# compiler to be installed on your system. The C# compiler (csc.exe) must be in the MSYS2 PATH.

To add it to the MSYS2 PATH, do the following:

export PATH="/c/WINDOWS/Microsoft.NET/Framework/v4.0.30319/":$PATH

The details will vary depending on which version of .NET you are using.

You can persist the above PATH changes across sessions by adding the above line to your ~/.bash_profile.

See README.CSharp.md for further details.

Using Mercury in the MSYS2 shell

This section describes how to use a Mercury compiler that was installed using the instructions in the previous section from within an MSYS2 environment. The MSYS2 environment that you run the compiler in must match the one it was built in (i.e. do not use a Mercury compiler built using the MINGW64 environment in the UCRT64 environment).

Add the Mercury bin directory to the MSYS2 PATH using a Unix-style path. For example, if Mercury is installed in "C:\mercury", then you would add /c/mercury/bin to the MSYS2 PATH. You cannot add a Windows-style path with a drive letter to the MSYS2 PATH since : is used as the path separator in MSYS2.

After the Mercury bin directory has been added to the MSYS2 PATH, then you should be able to use the compiler.

Note that while mmake does work in the MSYS2 shell, it is quite slow. This is largely due to the MSYS2 port of GNU cp being relatively slow on Windows filesystems. We suggest using mmc --make, which does not use cp by default, when possible.

Using Mercury in the Windows Command Prompt

This section describes how to use a Mercury compiler that was installed using the instructions above from the Windows Command Prompt (i.e. cmd.exe). Only Mercury compilers that are native Windows executables will work from the Windows Command Prompt or PowerShell. Mercury compilers built in the MSYS2 MSYS environment will not work from the Windows Command Prompt or PowerShell.

Ensure that the following directories are present in the Windows PATH:

1. The bin directory of the MSYS2 environment that you used to build Mercury.

   For the UCRT64 environment, this is C:\msys64\ucrt64\bin.
   For the MINGW64 environment, this is C:\msys64\mingw64\bin.
   For the MINGW32 environment, this is C:\msys64\mingw32\bin.
   For the CLANG64 environment, this is C:\msys64\clang64\bin.

2. The directory containing the Java toolchain (javac, jar and java), if the java grade was installed.

3. The directory containing the C# toolchain, if the csharp grade was installed.

4. The Mercury bin directory. For example, if Mercury is installed in C:\mercury, then you would add C:\mercury\bin to the Windows PATH.

Be careful about adding the above directories to the Windows System or User PATH. Doing so may result in conflicts between DLLs and executables in the MSYS2 bin directory and those installed elsewhere. A better approach is to create a batch file (e.g. mercury_env.bat) that sets the PATH for Mercury on a per-session basis.

You can then invoke the Mercury compiler using the command mercury. This is a batch file that is equivalent to mmc in other environments. We do not use mmc in the Windows Command Prompt because that name conflicts with the executable for the Microsoft Management Console.

For example, to build the "Hello, World" example in the samples directory of the Mercury distribution, do:

mercury hello.m

or, using the --make option:

mercury --make hello

Note that mmake is not supported in the Windows Command Prompt or PowerShell.

Missing libwinpthread-1.dll

This issue typically occurs when C grade executables are run outside of an MSYS2 shell (e.g. from cmd.exe or PowerShell). Executables run in cmd.exe may abort and display a Windows loader error dialog containing a message like the following:

The code execution cannot proceed because libwinpthread-1.dll was
not found. Reinstalling the program may fix this problem.

This happens because Windows cannot find libwinpthread-1.dll, which Mercury executables need. There are several possible resolutions:

1. Statically link against all libraries. This can be done by passing the option --linkage=static to the Mercury compiler. This will increase the size of the executables.

2. Modify the dynamic-link library search order on Windows to include the directory containing libwinpthread-1.dll. There are a lot of ways to do this, but the two simple ones are to either copy the file libwinpthread-1.dll into the same directory as the executable or to add the directory containing that DLL to the Windows PATH.

   For the UCRT64 MSYS2 environment, libwinpthread-1.dll is in the directory C:\msys64\ucrt64\bin. Add it to the Windows PATH by doing:

   set PATH=C:\msys64\ucrt64\bin;%PATH%
   

   For the MINGW64 MSYS2 environment, libwinpthread-1.dll is in the directory C:\msys64\mingw64\bin. Add it to the Windows PATH by doing:

   set PATH=C:\msys64\mingw64\bin;%PATH%
   

   For the MINGW32 MSYS2 environment, libwinpthread-1.dll is in the directory C:\msys64\mingw32\bin. Add it to the Windows PATH by doing:

   set PATH=C:\msys64\mingw32\bin;%PATH%
   

   For a more complete description of how Windows searches for DLLs, see the following documentation from Microsoft:

   https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-search-order

If you are running a Mercury executable from within PowerShell, then the same problem with a "missing" libwinpthread-1.dll can occur. In PowerShell, no error dialog is displayed. (PowerShell does not display the Windows loader error dialog for missing DLLs.) Instead, the value of the built-in variable $LASTEXITCODE is set to a non-zero value. This issue can be resolved in PowerShell using the same resolutions described above.

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