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Add an interface for initialization of vars without an explicit initializer (#6934)

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When a `var` is not explicitly given an initializer, initialize it in
one of two ways:

* If its type implements the new interface `Core.Default`, call
`Core.Default.Op` to initialize it.
* Otherwise, if its type implements `UnformedInit`, leave it in an
unformed state. For now, this is always an uninitialized state, but that
will change in the future.
* If neither of those apply, the `var` declaration is ill-formed.

This is a step towards implementing leads decision #6739 and proposals
#257 and #5913.

Assisted-by: Gemini 3.1 Pro via Antigravity

---------

Co-authored-by: Geoff Romer <gromer@google.com>
This commit is contained in:
Richard Smith
2026-03-19 23:46:06 +00:00
committed by GitHub
co-authored by Geoff Romer
parent fd2d210c63
commit ce50f181f1
146 changed files with 5226 additions and 3535 deletions
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toolchain/check/testdata/patterns/tuple.carbon
Vendored
+3 -2
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@@ -35,7 +35,7 @@ let (a: (), b: ()) = F();
library "[[@TEST_NAME]]";
var t: ((), ());
var t: ((), ()) = ((), ());
//@dump-sem-ir-begin
let (a: (), b: ()) = t;
//@dump-sem-ir-end
@@ -133,9 +133,9 @@ let (a: (), b: ()) = t;
// CHECK:STDOUT: %empty_tuple: %empty_tuple.type = tuple_value () [concrete]
// CHECK:STDOUT: %tuple.type: type = tuple_type (%empty_tuple.type, %empty_tuple.type) [concrete]
// CHECK:STDOUT: %pattern_type.5b8: type = pattern_type %tuple.type [concrete]
// CHECK:STDOUT: %pattern_type.cb1: type = pattern_type %empty_tuple.type [concrete]
// CHECK:STDOUT: %tuple.elem0: ref %empty_tuple.type = tuple_access file.%t.var, element0 [concrete]
// CHECK:STDOUT: %tuple.elem1: ref %empty_tuple.type = tuple_access file.%t.var, element1 [concrete]
// CHECK:STDOUT: %pattern_type.cb1: type = pattern_type %empty_tuple.type [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
@@ -164,6 +164,7 @@ let (a: (), b: ()) = t;
// CHECK:STDOUT:
// CHECK:STDOUT: fn @__global_init() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %t.ref: ref %tuple.type = name_ref t, file.%t [concrete = file.%t.var]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }