Requirements

garyo edited this page Dec 13, 2014 · 1 revision
  • Allow installing external tools (pip install or ...)
    • scons --version (or similar) should list installed tools and toolchains
    • missing external tools should give sensible errors
  • Tool setup must happen before reading SConstruct somehow
    • DefaultEnvironment and all new Environments should know about all tools
    • alternative: lazy-construct DefaultEnvironment
    • user-specified tools and toolchains need to be specifiable at beginning of build
  • User should be able to set default tools and toolchains
    • unused tools shouldn't take any startup time
  • Lazy init of tools and chains
    • This is faster because unused tools don't matter
    • It allows missing unused tools to not give errors, but missing used tools can (and should)
    • But it makes configuring environments much harder for users, because they can't override or append to tool-provided variables until those exist. This would break a lot of existing SConstructs.
    • We need to find some kind of compromise here:
      • Explicitly list tools required by build (where?): this should work well because only the needed tools will be initialized
      • if nothing explicitly specified, fall back to current method
  • Within a tool:
    • specify dependencies on other tools
    • detect existence on system reliably, and without modifying env
      • need better error messaging: ability to probe silently, but also give sensible errors when needed
    • constructor needs to allow args: version, path, ABI, etc. (this is important)
    • allow for common setup (all C compilers, etc.) as now
    • tools should be versioned so user can check if up to date, etc.
    • Let a tool declare beforehand which variables it accepts and defines on any platform, without actually completely initializing the tool.
      • Allows to define additional flags even when unused on the current platform.
      • Improves auto-generated tool docs
  • Tool chains:
    • either-or
    • and
    • collections
  • Platform
    • How much do we need to know about the platform, for tools to initialize themselves?
    • Cross-compilation comes into this, but may be too much to include as a general part of this project.
    • It may be useful to define toolchains and enable/disable them by platform
    • Of course the default toolchains need to be different by platform
    • It may be possible for a default toolchain to just search for all tools in a particular order and pick the first, as long as the tool-dependency system is robust enough.
  • Usability
    • $CC etc. must never be left blank (without a prior tool-missing error message at least) - this is a common problem
    • Must be backward compatible, at least for all common cases.
    • Must not require any new user files (e.g. something in site_scons) for normal operation
    • Need a clear guide on requirements for new tools
      • how to make a a tool
      • how to include tests
  • Considerations
    • "batteries included?"
      • Each tool should do its best to set itself up, find executables, etc.
      • What about SCons policy of not relying on $PATH? Maybe we should relax that or have an option?
    • minimum magic, maximum flexibility
    • what about single tools? Should every tool be required to be part of a toolchain (even if it's just one tool)? Maybe this doesn't matter much.
  • Non-goals:
    • New command-line args like autotools (platform, install paths, etc.). We should build something that would enable that, but it's too much to bite off now.
    • Persistence -- remember configuration on disk between runs. This is a performance enhancement which we should address only once we know it's needed. Better if we can design a system that's fast without needing this.
  • References:
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