cached
A build script that lists a directory to decide what to build, and never tells Zig’s configure cache.
var dir = try b.root.openDir(b.graph.io, "test", .{ .iterate = true });
defer dir.close(b.graph.io);
var it = dir.iterate();
while (try it.next(b.graph.io)) |entry| { ... } // one addTest per file
Zig 0.17 caches the configure phase: when nothing it tracks has changed, zig build reuses the last build graph without running build(). A file added to test/ changes nothing it tracks, so its test is never built, and zig build test passes without running it, until something else invalidates the cache: an edit to build.zig, a new option. It compiles clean in every build mode, and works on every run that configures anew, such as the first one after a clone.
The fix is b.dependOnDirectoryContents(b.path("test")); next to the openDir, which makes the directory’s entries something the cache tracks, or b.graph.poisonCache(), which turns the cache off for the build. dependOnDirectoryContents is not recursive: a walk needs one for each directory it enters as well.
What cached reports
A call to openDir with .iterate = true in its options and b.root in it, in a function with a *std.Build parameter b: b.root.openDir(...), b.root.root_dir.handle.openDir(...), or cwd().openDir(io, try b.root.joinString(...), ...). It is reported when the function calls none of dependOnDirectoryContents, dependOnDirectoryMetadata and poisonCache; or, when it also calls walk or walkSelectively, which go into subdirectories, when no dependOnDirectory... call of it is in a loop, as one for each directory the walk enters is.
Not reported: b.build_root, the field of a Zig before 0.17, whose configure phase always runs; a directory opened by another path (cwd().openDir(io, "test", ...), openDirAbsolute), which the syntax cannot place in the build root or a Zig version; and a dependency the caller declares, which only the caller shows.
Found in real code
Over Zig 0.17.0’s standard library and compiler sources and the application repos, cached reports nothing. Over fourteen well-known public Zig projects, seven, all real, in a terminal emulator, an event loop library and a static site generator, whose build scripts list a directory of tests, examples or sources to decide what to build and never tell Zig 0.17’s configure cache.