-- premake5.lua

-- This file describes the build configuration for Slang so
-- that premake can generate platform-specific build files
-- using Premake 5 (https://premake.github.io/).
--
-- To update the build files that are checked in to the Slang repository,
-- run a `premake5` binary and specify the appropriate action, e.g.:
--
--      premake5.exe --os=windows vs2015
--
-- If you are trying to build Slang on another platform, then you
-- can try invoking `premake5` for your desired OS and build format
-- and see what happens.
--
-- If you are going to modify this file to change/customize the Slang
-- buidl, then you may need to read up on Premake's approach and
-- how it uses/abuses Lua syntax. A few important things to note:
--
-- * Everything that *looks* like a declarative (e.g., `kind "SharedLib"`)
-- is actually a Lua function call (e.g., `kind("SharedLib")`) that
-- modifies the behind-the-scenes state that describes the build.
--
-- * Many of these function calls are "sticky" and affect subsequent
-- calls, so ordering matters a *lot*. This file uses indentation to
-- represent some of the flow of state, but it is important to recognize
-- that the indentation is not semantically significant.
--
-- * Because the configuration logic is just executable Lua code, we
-- can capture and re-use bits of configuration logic in ordinary
-- Lua subroutines.
--
-- Now let's move on to the actual build:

-- The "workspace" represents the overall build (the "solution" in
-- Visual Studio terms). It sets up basic build settings that will
-- apply across all projects.
--
workspace "slang"
    -- We will support debug/release configuration and x86/x64 builds.
    configurations { "Debug", "Release" }
    platforms { "x86", "x64" }

    -- The output binary directory will be derived from the OS
    -- and configuration options, e.g. `bin/windows-x64/debug/`
    targetdir "bin/%{cfg.system}-%{cfg.platform:lower()}/%{cfg.buildcfg:lower()}"

    -- The intermediate ("object") directory will use a similar
    -- naming scheme to the output directory, but will also use
    -- the project name to avoid cases where multiple projects
    -- have source files with the same name.
    objdir "intermediate/%{cfg.system}-%{cfg.platform:lower()}/%{cfg.buildcfg:lower()}/%{prj.name}"

    -- Statically link to the C/C++ runtime rather than create a DLL dependency.
    flags { "StaticRuntime" }

    -- Once we've set up the common settings, we will make some tweaks
    -- that only apply in a subset of cases. Each call to `filter()`
    -- changes the "active" filter for subsequent commands. In
    -- effect, those commands iwll be ignored when the conditions of
    -- the filter aren't satisfied.

    -- Our `x64` platform should (obviously) target the x64
    -- architecture and similarly for x86.
    filter { "platforms:x64" }
        architecture "x64"
    filter { "platforms:x86" }
        architecture "x86"

    -- When compiling the debug configuration, we want to turn
    -- optimization off, make sure debug symbols are output,
    -- and add the same preprocessor definition that VS
    -- would add by default.
    filter { "configurations:debug" }
        optimize "Off"
        symbols "On"
        defines { "_DEBUG" }

    -- For the release configuration we will turn optimizations on
    -- (we do not yet micro-manage the optimization settings)
    -- and set the preprocessor definition that VS would add by default.
    filter { "configurations:release" }
        optimize "On"
        defines { "NDEBUG" }

--
-- We are now going to start defining the projects, where
-- each project builds some binary artifact (an executable,
-- library, etc.).
--
-- All of our projects follow a common structure, so rather
-- than reiterate a bunch of build settings, we define
-- some subroutines that make the configuration as concise
-- as possible.
--
-- First, we will define a helper routine for adding all
-- the relevant files from a given directory path:
--
function addSourceDir(path)
    files
    {
        path .. "/*.cpp",       -- C++ source files
        path .. "/*.slang",     -- Slang files (for our stdlib)
        path .. "/*.h",         -- Header files
        path .. "/*.hpp",       -- C++ style headers (for glslang)
        path .. "/*.natvis",    -- Visual Studio debugger visualization files
    }
end
--
-- Next we will define a helper routine that all of our
-- projects will bottleneck through. Here `name` is
-- the name for the project (and the base name for
-- whatever output file it produces), while `baseDir`
-- is the parent directory of the project's directory.
--
-- E.g., for the `slangc` project, the source code
-- is nested in `source/`, so we'd (indirectly) call:
--
--      baseSlangProject("slangc", "source")
--
function baseSlangProject(name, baseDir)

    -- The project directory will be nested inside
    -- the base directory using the project's name.
    --
    local projectDir = baseDir .. "/" .. name

    -- Start a new project in premake. This switches
    -- the "current" project over to the newly created
    -- one, so that subsequent commands affect this project.
    --
    project(name)

    -- Set the location where the project file will be placed.
    -- We set the project files to reside in their source
    -- directory, because in Visual Studio the default
    -- working directory when launching a project in the
    -- debugger is its project directory. This ensures that
    -- examples will work as expected for VS users.
    --
    -- TODO: consider only setting this for examples, since
    -- it is less relevant to other projects.
    --
    location(projectDir)

    -- All of our projects are written in C++.
    --
    language "C++"

    -- Since we know the project directory, we can go ahead
    -- and add any source files locate there.
    --
    -- Note that we do *not* recurse into subdirectories,
    -- so projects that spread their source over multiple
    -- directories will need to take more steps.
    --
    addSourceDir(projectDir)

    -- By default, Premake generates VS project files that
    -- reflect the directory structure of the source code.
    -- While this is nice in principle, it creates messy
    -- results in practice for our projects.
    --
    -- Instead, we will use the `vpaths` feature to imitate
    -- the default VS behavior of grouping files into
    -- virtual subdirectories (VS calls them "filters") for
    -- header and source files respectively.
    --
    -- Note: We are setting `vpaths` using a list of key/value
    -- tables instead of just a key/value table, since this
    -- appears to be an (undocumented) way to fix the order
    -- in which the filters are tested. Otherwise we have
    -- issues where premake will nondeterministically decide
    -- the check something against the `**.cpp` filter first,
    -- and decide that a `foo.cpp.h` file should go into
    -- the `"Source Files"` vpath. That behavior seems buggy,
    -- but at least we appear to have a workaround.
    --
    vpaths {
       { ["Header Files"] = { "**.h", "**.hpp"} },
       { ["Source Files"] = { "**.cpp", "**.slang", "**.natvis" } },
    }
end

-- We can now use the `baseSlangProject()` subroutine to
-- define helpers for the different categories of project
-- in our source tree.
--
-- For example, the Slang project has several tools that
-- are used during building/testing, but don't need to
-- be distributed. These always have their source code in
-- `tools/<project-name>/`.
--
function tool(name)
    -- We use the `group` command here to specify that the
    -- next project we create shold be placed into a group
    -- named "tools" in a generated IDE solution/workspace.
    --
    -- This is used in the generated Visual Studio solution
    -- to group all the tools projects together in a logical
    -- sub-directory of the solution.
    --
    group "tools"

    -- Now we invoke our shared project configuration logic,
    -- specifying that the project lives under the `tools/` path.
    --
    baseSlangProject(name, "tools")

    -- Finally, we set the project "kind" to produce a console
    -- application. This is a reasonable default for tools,
    -- and it can be overriden because Premake is stateful,
    -- and a subsequent call to `kind()` would overwrite this
    -- default.
    --
    kind "ConsoleApp"
end

-- "Standard" projects will be those that go to make the binary
-- packages for slang: the shared libraries and executables.
--
function standardProject(name)
    -- Because Premake is stateful, any `group()` call by another
    -- project would still be in effect when we create a project
    -- here (e.g., if somebody had called `tool()` before
    -- `standardProject()`), so we are careful here to set the
    -- group to an emptry string, which Premake treats as "no group."
    --
    group ""

    -- A standard project has its code under `source/`
    --
    baseSlangProject(name, "source")
end

-- Finally we have the example programs that show how to use Slang.
--
function example(name)
    -- Example programs go into an "example" group
    group "examples"

    -- They have their source code under `examples/<project-name>/`
    baseSlangProject(name, "examples")

    -- By default, all of our examples are GUI applications. One some
    -- platforms there is no meaningful distinction between GUI and
    -- command-line applications, but it is significant on Windows and MacOS
    --
    kind "WindowedApp"

    -- Every example needs to be able to include the `slang.h` header
    -- if it is going to use Slang, so we might as well set up a suitable
    -- include path here rather than make each example do it.
    --
    includedirs { "." }

    -- The examples also need to link against the slang library,
    -- so we specify that here rather than in each example.
    links { "slang" }
end

--
-- With all of these helper routines defined, we can now define the
-- actual projects quite simply. For example, here is the entire
-- declaration of the "Hello, World" example project:
--
example "hello"
    uuid "E6385042-1649-4803-9EBD-168F8B7EF131"
--
-- Note how we are calling our custom `example()` subroutine with
-- the same syntax sugar that Premake usually advocates for their
-- `project()` function. This allows us to treat `example` as
-- a kind of specialized "subclass" of `project`
--
-- The call to `uuid()` in the definition of `hello` establishes
-- the UUID/GUID that will be used for the project in generated
-- formats that use these as unique identifiers (e.g., Visual
-- Studio solutions). Without this call, Premake will generate
-- a fresh UUID for a project each time its generation logic
-- runs, which can create spurious diffs.
--

-- Most of the other projects have more interesting configuration going
-- on, so let's walk through them in order of increasing complexity.
--
-- The `core` project is a static library that has all the basic types
-- and routines that get shared across both the Slang compiler/runtime
-- and the various tool projects. It's build is pretty simple:
--

standardProject "core"
    uuid "F9BE7957-8399-899E-0C49-E714FDDD4B65"
    kind "StaticLib"

    -- For our core implementation, we want to use the most
    -- aggressive warning level supported by the target, and
    -- to treat every warning as an error to make sure we
    -- keep our code free of warnings.
    --
    warnings "Extra"
    flags { "FatalWarnings" }


--
-- `slang-generate` is a tool we use for source code generation on
-- the compiler. It depends on the `core` library, so we need to
-- declare that:
--

tool "slang-generate"
    uuid "66174227-8541-41FC-A6DF-4764FC66F78E"
    links { "core" }


--
-- The `slang-test` test driver also uses the `core` library, and it
-- currently relies on include paths being set up so that it can find
-- the core headers:
--

tool "slang-test"
    uuid "0C768A18-1D25-4000-9F37-DA5FE99E3B64"
    includedirs { "." }
    links { "core" }

--
-- The reflection test harness `slang-reflection-test` is pretty
-- simple, in that it only needs to link against the slang library
-- to do its job:
--

tool "slang-reflection-test"
    uuid "22C45F4F-FB6B-4535-BED1-D3F5D0C71047"
    includedirs { "." }
    links { "slang" }

--
-- `slang-eval-test` is similarly easy to build:
--
-- Note: `slang-eval-test` will probably be deprecated and its functionality
-- folded into `render-test`, but we aren't ready for that just yet.
--

tool "slang-eval-test"
    uuid "205FCAB9-A13F-4980-86FA-F6221A7095EE"
    includedirs { "." }
    links { "core", "slang" }

--
-- The most complex testing tool we have is `render-test`, but from
-- a build perspective the most interesting thing about it is that for
-- our Windows build it requires a Windows 10 SDK.
--
-- TODO: Try to make the build not require a fixed version of the Windows SDK.
-- Ideally we should just specify a *minimum* version.
--
-- This test also requires Vulkan headers which we've placed in the
-- `external/` directory, and it also includes files from the `core`
-- library in ways that require us to set up `source/` as an include path.
--
-- TODO: Fix that requirement.
--

tool "render-test"
    uuid "96610759-07B9-4EEB-A974-5C634A2E742B"
    includedirs { ".", "external", "source" }
    links { "core", "slang" }
    filter { "system:windows" }
        systemversion "10.0.14393.0"

--
-- The `slangc` command-line application is just a very thin wrapper
-- around the Slang dynamic library, so its build is extermely simple.
-- One windows `slangc` uses the the `core` library for some UTF-16
-- to UTF-8 string conversion before calling into `slang.dll`, so
-- it also depends on `core`:
--

standardProject "slangc"
    uuid "D56CBCEB-1EB5-4CA8-AEC4-48EA35ED61C7"
    kind "ConsoleApp"
    links { "core", "slang" }

--
-- TODO: Slang's current `Makefile` build does some careful incantations
-- to make sure that the binaries it generates use a "relative `RPATH`"
-- for loading shared libraries, so that Slang is not dependent on
-- being installed to a fixed path on end-user machines. Before we
-- can use Premake for the Linux build (or evenatually MacOS) we would
-- need to figure out how to replicate this incantation in premake.
--

--
-- Now that we've gotten all the simple projects out of the way, it is time
-- to get into the more serious build steps.
--
-- First up is the `slang` dynamic library project:
--

standardProject "slang"
    uuid "DB00DA62-0533-4AFD-B59F-A67D5B3A0808"
    kind "SharedLib"
    links { "core" }
    warnings "Extra"
    flags { "FatalWarnings" }

    -- The way that we currently configure things through `slang.h`,
    -- we need to set a preprocessor definitions to ensure that
    -- we declare the Slang API functions for *export* and not *import*.
    --
    defines { "SLANG_DYNAMIC_EXPORT" }

    -- The `standardProject` operation already added all the code in
    -- `source/slang/*`, but we also want to incldue the umbrella
    -- `slang.h` header in this prject, so we do that manually here.
    files { "slang.h" }

    -- The most challenging part of building `slang` is that we need
    -- to invoke the `slang-generate` tool to generate the version
    -- of the Slang standard library that we embed into the compiler.
    --
    -- First, we need to ensure that `slang-generate` gets built
    -- before `slang`, so we declare a non-linking dependency between
    -- the projects here:
    --
    dependson { "slang-generate" }

    -- Next, we want to add a custom build rule for each of the
    -- files that makes up the standard library. Those are
    -- always named `*.meta.slang`, so we can select for them
    -- using a `filter` and then use Premake's support for
    -- defining custom build commands:
    --
    filter "files:**.meta.slang"
        -- Specify the "friendly" message that should print to the build log for the action
        buildmessage "slang-generate %{file.relpath}"

        -- Specify the actual command to run for this action.
        --
        -- Note that we use a single-quoted Lua string and wrap the path
        -- to the `slang-generate` command in double quotes to avoid
        -- confusing the Windows shell. It seems that Premake outputs that
        -- path with forward slashes, which confused the shell if we don't
        -- quote the executable path.
        --
        buildcommands { '"%{cfg.targetdir}/slang-generate" %{file.relpath}' }

        -- Given `foo.meta.slang` we woutput `foo.meta.slang.h`.
        -- This needs to be specified because the custom action will only
        -- run when this file needs to be generated.
        --
        buildoutputs { "%{file.relpath}.h" }

        -- We will specify an additional build input dependency on the `slang-generate`
        -- tool itself, so that changes to the code for the tool cause the generation
        -- step to be re-run.
        --
        -- In order to get the file name right, we need to know the executable suffix
        -- that the target platform will use. Premake might have a built-in way to
        -- query this, but I couldn't find it, so I am just winging it for now:
        --
        local executableSuffix = "";
        if(os.target() == "windows") then
            executableSuffix = ".exe";
        end
        --
        buildinputs { "%{cfg.targetdir}/slang-generate" .. executableSuffix }

--
-- The single most complicated part of our build is our custom version of glslang.
-- Is not really set up to produce a shared library with a usable API, so we have
-- our own custom shim API around it to invoke GLSL->SPIRV compilation.
--
-- Glslang normally relies on a CMake-based build process, and its code is spread
-- across multiple directories with implicit dependencies on certain command-line
-- definitions.
--
-- The following is a tailored build of glslang that pulls in the pieces we care
-- about whle trying to leave out the rest:
--
standardProject "slang-glslang"
    uuid "C495878A-832C-485B-B347-0998A90CC936"
    kind "SharedLib"
    includedirs { "external/glslang" }

    defines
    {
        -- `ENABLE_OPT` must be defined (to either zero or one) for glslang to compile at all
        "ENABLE_OPT=0",

        -- We want to build a version of glslang that supports every feature possible,
        -- so we will enable all of the supported vendor-specific extensions so
        -- that they can be used in Slang-generated GLSL code when required.
        --
        "AMD_EXTENSIONS",
        "NV_EXTENSIONS",
    }

    -- We will add source code from every directory that is required to get a
    -- minimal GLSL->SPIR-V compilation path working.
    addSourceDir("external/glslang/glslang/GenericCodeGen")
    addSourceDir("external/glslang/glslang/MachineIndependent")
    addSourceDir("external/glslang/glslang/MachineIndependent/preprocessor")
    addSourceDir("external/glslang/glslang/OSDependent")
    addSourceDir("external/glslang/OGLCompilersDLL")
    addSourceDir("external/glslang/SPIRV")
    addSourceDir("external/glslang/StandAlone")

    -- Unfortunately, blindly adding files like that also pulled in a declaration
    -- of a main entry point that we do *not* want, so we will specifically
    -- exclude that file from our build.
    removefiles { "external/glslang/StandAlone/StandAlone.cpp" }

    -- Glslang includes some platform-specific code around DLL setup/teardown
    -- and handling of thread-local storage for its multi-threaded mode. We
    -- don't really care about *any* of that, but we can't remove it from the
    -- build so we need to include the appropriate platform-specific sources.

    filter { "system:windows" }
        -- On Windows we need to add the platform-specific sources and then
        -- remove the `main.cpp` file since it tries to define a `DllMain`
        -- and we don't want the default glslang one.
        addSourceDir( "external/glslang/glslang/OSDependent/Windows" )
        removefiles { "external/glslang/glslang/OSDependent/Windows/main.cpp" }

    filter { "system:linux" }
        addSourceDir("external/glslang/glslang/OSDependent/Unix")

--
-- With glslang's build out of the way, we've now covered everything we have
-- to build to get Slang and its tools/examples built.
--
-- What is not included in this file yet is support for any custom `make`
-- targets for:
--
-- * Invoking the test runner
-- * Packaging up binaries
-- * "Installing" Slang on a user's machine
--