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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/interop/cpp/function/struct.carbon
Vendored
+34 -2
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@@ -651,6 +651,12 @@ fn F() {
// CHECK:STDOUT: %ptr.edf: type = ptr_type %S [concrete]
// CHECK:STDOUT: %foo__carbon_thunk.type: type = fn_type @foo__carbon_thunk [concrete]
// CHECK:STDOUT: %foo__carbon_thunk: %foo__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %DefaultOrUnformed.type: type = facet_type <@DefaultOrUnformed> [concrete]
// CHECK:STDOUT: %T: type = symbolic_binding T, 0 [symbolic]
// CHECK:STDOUT: %T.as.DefaultOrUnformed.impl.Op.type.6c6: type = fn_type @T.as.DefaultOrUnformed.impl.Op, @T.as.DefaultOrUnformed.impl(%T) [symbolic]
// CHECK:STDOUT: %T.as.DefaultOrUnformed.impl.Op.ae1: %T.as.DefaultOrUnformed.impl.Op.type.6c6 = struct_value () [symbolic]
// CHECK:STDOUT: %DefaultOrUnformed.impl_witness.590: <witness> = impl_witness imports.%DefaultOrUnformed.impl_witness_table, @T.as.DefaultOrUnformed.impl(%S) [concrete]
// CHECK:STDOUT: %DefaultOrUnformed.facet: %DefaultOrUnformed.type = facet_value %S, (%DefaultOrUnformed.impl_witness.590) [concrete]
// CHECK:STDOUT: %S.cpp_destructor.type: type = fn_type @S.cpp_destructor [concrete]
// CHECK:STDOUT: %S.cpp_destructor: %S.cpp_destructor.type = struct_value () [concrete]
// CHECK:STDOUT: }
@@ -672,6 +678,8 @@ fn F() {
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: %Core.import_ref.01d: @T.as.DefaultOrUnformed.impl.%T.as.DefaultOrUnformed.impl.Op.type (%T.as.DefaultOrUnformed.impl.Op.type.6c6) = import_ref Core//prelude/parts/default, loc{{\d+_\d+}}, loaded [symbolic = @T.as.DefaultOrUnformed.impl.%T.as.DefaultOrUnformed.impl.Op (constants.%T.as.DefaultOrUnformed.impl.Op.ae1)]
// CHECK:STDOUT: %DefaultOrUnformed.impl_witness_table = impl_witness_table (%Core.import_ref.01d), @T.as.DefaultOrUnformed.impl [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @F(%s.param: %S) {
@@ -687,7 +695,15 @@ fn F() {
// CHECK:STDOUT: %x.var_patt: %pattern_type.cd8 = var_pattern %x.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %x.var: ref %S = var %x.var_patt
// CHECK:STDOUT: %.loc10: type = splice_block %S.ref.loc10 [concrete = constants.%S] {
// CHECK:STDOUT: %DefaultOrUnformed.facet: %DefaultOrUnformed.type = facet_value constants.%S, (constants.%DefaultOrUnformed.impl_witness.590) [concrete = constants.%DefaultOrUnformed.facet]
// CHECK:STDOUT: %.loc10_24.1: %DefaultOrUnformed.type = converted constants.%S, %DefaultOrUnformed.facet [concrete = constants.%DefaultOrUnformed.facet]
// CHECK:STDOUT: %as_type: type = facet_access_type %.loc10_24.1 [concrete = constants.%S]
// CHECK:STDOUT: %.loc10_24.2: type = converted %.loc10_24.1, %as_type [concrete = constants.%S]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %.loc10_3: ref %S = splice_block %x.var {}
// CHECK:STDOUT: %T.as.DefaultOrUnformed.impl.Op.call: init %S to %.loc10_3 = call %T.as.DefaultOrUnformed.impl.Op.specific_fn()
// CHECK:STDOUT: assign %x.var, %T.as.DefaultOrUnformed.impl.Op.call
// CHECK:STDOUT: %.loc10_22: type = splice_block %S.ref.loc10 [concrete = constants.%S] {
// CHECK:STDOUT: %Cpp.ref.loc10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %N.ref.loc10: <namespace> = name_ref N, imports.%N [concrete = imports.%N]
// CHECK:STDOUT: %S.ref.loc10: type = name_ref S, imports.%S.decl [concrete = constants.%S]
@@ -757,6 +773,12 @@ fn F() {
// CHECK:STDOUT: %foo__carbon_thunk.type: type = fn_type @foo__carbon_thunk [concrete]
// CHECK:STDOUT: %foo__carbon_thunk: %foo__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %pattern_type.cff: type = pattern_type %O [concrete]
// CHECK:STDOUT: %DefaultOrUnformed.type: type = facet_type <@DefaultOrUnformed> [concrete]
// CHECK:STDOUT: %T: type = symbolic_binding T, 0 [symbolic]
// CHECK:STDOUT: %T.as.DefaultOrUnformed.impl.Op.type.6c6: type = fn_type @T.as.DefaultOrUnformed.impl.Op, @T.as.DefaultOrUnformed.impl(%T) [symbolic]
// CHECK:STDOUT: %T.as.DefaultOrUnformed.impl.Op.ae1: %T.as.DefaultOrUnformed.impl.Op.type.6c6 = struct_value () [symbolic]
// CHECK:STDOUT: %DefaultOrUnformed.impl_witness.938: <witness> = impl_witness imports.%DefaultOrUnformed.impl_witness_table, @T.as.DefaultOrUnformed.impl(%O) [concrete]
// CHECK:STDOUT: %DefaultOrUnformed.facet: %DefaultOrUnformed.type = facet_value %O, (%DefaultOrUnformed.impl_witness.938) [concrete]
// CHECK:STDOUT: %O.cpp_destructor.type: type = fn_type @O.cpp_destructor [concrete]
// CHECK:STDOUT: %O.cpp_destructor: %O.cpp_destructor.type = struct_value () [concrete]
// CHECK:STDOUT: }
@@ -774,6 +796,8 @@ fn F() {
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: %Core.import_ref.01d: @T.as.DefaultOrUnformed.impl.%T.as.DefaultOrUnformed.impl.Op.type (%T.as.DefaultOrUnformed.impl.Op.type.6c6) = import_ref Core//prelude/parts/default, loc{{\d+_\d+}}, loaded [symbolic = @T.as.DefaultOrUnformed.impl.%T.as.DefaultOrUnformed.impl.Op (constants.%T.as.DefaultOrUnformed.impl.Op.ae1)]
// CHECK:STDOUT: %DefaultOrUnformed.impl_witness_table = impl_witness_table (%Core.import_ref.01d), @T.as.DefaultOrUnformed.impl [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @F(%s.param: %S) {
@@ -789,7 +813,15 @@ fn F() {
// CHECK:STDOUT: %x.var_patt: %pattern_type.cff = var_pattern %x.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %x.var: ref %O = var %x.var_patt
// CHECK:STDOUT: %.loc9: type = splice_block %O.ref.loc9 [concrete = constants.%O] {
// CHECK:STDOUT: %DefaultOrUnformed.facet: %DefaultOrUnformed.type = facet_value constants.%O, (constants.%DefaultOrUnformed.impl_witness.938) [concrete = constants.%DefaultOrUnformed.facet]
// CHECK:STDOUT: %.loc9_22.1: %DefaultOrUnformed.type = converted constants.%O, %DefaultOrUnformed.facet [concrete = constants.%DefaultOrUnformed.facet]
// CHECK:STDOUT: %as_type: type = facet_access_type %.loc9_22.1 [concrete = constants.%O]
// CHECK:STDOUT: %.loc9_22.2: type = converted %.loc9_22.1, %as_type [concrete = constants.%O]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %.loc9_3: ref %O = splice_block %x.var {}
// CHECK:STDOUT: %T.as.DefaultOrUnformed.impl.Op.call: init %O to %.loc9_3 = call %T.as.DefaultOrUnformed.impl.Op.specific_fn()
// CHECK:STDOUT: assign %x.var, %T.as.DefaultOrUnformed.impl.Op.call
// CHECK:STDOUT: %.loc9_20: type = splice_block %O.ref.loc9 [concrete = constants.%O] {
// CHECK:STDOUT: %Cpp.ref.loc9: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %O.ref.loc9: type = name_ref O, imports.%O.decl [concrete = constants.%O]
// CHECK:STDOUT: }