Hi, I think it would be interesting to have a compiler flag to inject imports into all compiling .d files.

This would be basically just extending the built-in implicit import object; that's in every non-betterC D file with any custom file you, or the build tool, might want to add.

Use cases:

• small application templates/modes with common imports set (like std.stdio, std.conv, std.algorithm, std.array, std.format) so you can more easily and quickly prototype (C# 10 / .NET 6 for example added this with implicit usings, though I'm not a fan because C# is just not that good at quick prototyping like D is)

• better DUB environment injection:

  • allow to pass in package version (usually built from git tag + commit hash, or when fetched the actual version) - this currently needs workarounds by invoking some preBuildCommands, which may not work on every target machine (e.g. DCD, D-Scanner, dfmt invoking rdmd, which is usually installed, but for example not on linux distros that package each tool individually)
  • allow to define manifest constants for different features (like build config name, configuration name, passed in architecture/triple, custom defined strings from dub.json)
  • possibility to publish packages that could have a flag to inject into the global namespace, for very common stuff or debugging stuff like custom asserts
  • additionally to the Have_xyz versions we could define enum string xyz_version = "1.2.3"; to allow dependencies to act differently based on package versions
    • we could additionally expose a dubHave("packageName", "minVersion") function for conditional compilation
  • expose build options, flags, requirements, toolchain info, etc.

• allows to define special UDAs as a kind of UDA stdlib that could be used for linting, auto completion hints, static analysis etc. Think of:

  • @nullable for reference types
  • standard @suppressWarning("...") for D-Scanner or other linters
  • common, interoperable @optional, @required UDAs for all serialization libraries (maybe as a library though)

Do you like this idea? Have any suggestions? Concerns?