I don't think the SQLite authors actually edit the single giant source file directly. Their source control repository has the code split up into many separate files, which are combined into "the amalgamation" by a build script: https://github.com/sqlite/sqlite/tree/master/src
yeah i saw that afterwards. they do it to squeeze more optimization out of the compiler by putting everything in one compilation unit. given the prominence of the library i have to wonder if this was an input to zig's behind-the-scenes single compilation unit design choice...
