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Write -betterC (@betterC) tests ​

@betterC marks a test as runnable without druntime. Such tests run normally under dub test, and --better-c additionally extracts them into a standalone program compiled with -betterC and executes it:

bash
dub test :base -- --better-c \
    --include-import=sparkles.base.text --include-import=std.ascii
console
 > text.readers.readInteger.advancesOnSuccess [libs/base/src/sparkles/base/text/readers.d:122]
 ...
7 @betterC tests passed

A failing assert aborts with the original file:line (the generated code carries #line directives):

console
betterc_tests: libs/base/src/.../readers.d:124: Assertion `r.hasValue' failed.

Wiring in the tested module ​

Import the attribute unconditionally (not under version (unittest)): the compiler resolves unittest UDAs even in builds that skip the bodies.

d
import sparkles.test_runner.attributes : betterC;

@("text.readers.tryConsume")
@betterC @safe pure nothrow @nogc
unittest { /* ... */ }

What an extracted test can use ​

The generated program imports the test's module and re-emits the test body as a named function, so the body can only reference:

  • the module's public symbols (module-scope private imports are invisible — add body-local imports for anything else);
  • templates and CTFE-able code by default — non-template functions live in object code that is not linked in;
  • non-template functions of modules explicitly compiled in with --include-import=<pattern> (maps to the compiler's -i=<pattern>). Included modules must be betterC-codegen-clean: no GC allocations, exceptions, or TypeInfo in any of their non-template functions.

There is deliberately no blanket "include everything" default: the moment any transitively imported module is not betterC-clean (e.g. anything touching std.uni), a blanket include breaks the build. Opt modules in precisely.

Toolchain ​

--compiler=<dc> (or $DC) picks the compiler; ldc2 then dmd from $PATH is the default. Import paths are derived from the discovered tests' module/file pairs plus a best-effort dub describe; add unusual roots with -I/--import-path. --keep preserves the generated program for inspection.