SConstruct not recognizing that a piped action requires a certain executable to run

[awa5114]

I have a directory with the following contents:

|   file.in
|   SConstruct.py
|   
\---modify
        modify.cpp
        SConscript.py

Here are the contents of each file:

file.in

in file

SConstruct.py

SConscript(["modify/SConscript.py"])


Command(
    "file.out",
    "file.in",
    action = [
        Copy("tempfile", "$SOURCE"),
        ".\modify.exe tempfile appendtext",
        Copy("$TARGET", "tempfile")
    ]
)

modify/modify.cpp

#include <iostream>
#include <fstream>
#include <filesystem>

int main(int argc, char* argv[])
{
    std::filesystem::path currentPath = std::filesystem::current_path();
    std::filesystem::path fullPath = currentPath / argv[1];
   
    if (!std::filesystem::exists(fullPath))
    {
        std::cout << "File doesn't exist, aborting" << std::endl;
        return 1;
    }

    std::ofstream outfile;
    outfile.open(fullPath.string(), std::ios_base::app);

    outfile << argv[2] << std::endl;

    return 0;
}

modify/SConscript.py

env = Environment(tools=["mingw"])

env.Program("modify.cpp")
Command("../modify.exe", "modify.exe", Copy("$TARGET", "$SOURCE"))

The idea here is to compile modify.cpp to modify.exe, copy modify.exe to the root folder and then run it against file.in to generate a new file. However when I run scons the SConstruct executes the Copy command first, and then naturally runs into a problem because modify.cpp has not been compiled yet:

scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
Copy("tempfile", "file.in")
.\modify.exe tempfile appendtext
'.\modify.exe' is not recognized as an internal or external command,
operable program or batch file.
scons: *** [file.out] Error 1
scons: building terminated because of errors.

What am I doing wrong here and why doesn't SCons recognize that Command needs modify.exe to be able to run? Thanks

[dmoody256]

I see a couple problems here:

1. you are using platform specific suffixes in your SConscript, now it is not portable. SCons will handle prefixes/suffixes for you automatically.
2. You have a directory which is potentially the same as a file target on linux (where program suffixes are nothing). In scons everything is a target and so there is no way differentiate a string target "modify" from the directory or file reference. You should change the name of your directory, something like modify_app or modify_tool. SCons could be made to work in this fashion but you will be hindering yourself because you will not be able to use the generic string target like modify.
3. The answer for the main question why doesn't SCons recognize that Command needs modify.exe is because it is not listed as a source. You can should add it as a source to your command.

Here are my suggested changes:

modify_app/SConscript.py

env = Environment(tools=["mingw"])

modify_node = env.Program(target='#/modify', source="modify.cpp")
Return("modify_node")

SConstruct.py

import os

env = Environment()

env['MODIFY'] = SConscript(["modify_app/SConscript"])

env['ENV']['PATH'] += f"{os.pathsep}." # so Command can execute 'modify'

env.Command(
    "file.out",
    ["$MODIFY", "file.in"],
    action = [
        Copy("tempfile", "${SOURCES[1]}"),
        "${SOURCES[0]} tempfile appendtext",
        Copy("$TARGET", "tempfile")
    ]
)