#19730 Introduce call-by-name syntax for `@rules` Issue created by stuhood (as motivated in #18905) Implementation: 1.

rule_graph

crate changes: • adjust the definition of

Get

(

DependencyKey

) for rule-graph solving to accept a fixed name/identifier for the rule to use, and some/all of its positional arguments • adjust graph solving to use the explicitly specified arguments to skip solving 2. syntax changes: • adjust the rule visitor (

AwaitableCollector

) to support extracting directly called

@rules

, in addition to the existing support for "rule helpers" • introduce an

implicitly(..)

builtin, which takes arguments similar to

Get(TypeName, ..)

• add support for positional arguments to

@rule

calls • implement support for call-by-name in

MultiGet

syntax • expose intrinsics as call-by-name (#20874) • determine new

@union

-usage syntax (or keep it type driven) 3. runtime changes: • adjust the

@rule

decorator such that when it has been called directly (i.e., not called with some secret-handshake), it trampolines back out to fill the additional positional arguments and to begin memoization • applies to both

async def

and

def

@rules

, since the act of memoizing can potentially mean blocking to wait for a result computed by another task • Use the

@rule

ids introduced in #19755 to drive

@rule

solving 4. deployment: • #20572 - add a

pants

-builtin goal which will execute a rewrite of one or more specified plugins or files from

await Get(TypeName, ..)

->

await rule_name(.., **implicitly(..))

• this requires rule-graph solving first (to select the

@rule

to use at each

Get

callsite), so the rewritten file must actually have been loaded • #21065 - migrate pants' code • Audit and change

@rule

names that are widely used in plugins/in-repo-backends in cases where they are not sufficiently descriptive. • Update docs for new syntax pantsbuild/pants