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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/lower/testdata/interop/cpp/parameters.carbon
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+11
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@@ -114,6 +114,7 @@ fn PassValueExpr(y: Cpp.Y) {
// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
// CHECK:STDOUT:
// CHECK:STDOUT: @_Cc.Main = global i16 0
// CHECK:STDOUT: @llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 0, ptr @_C__global_init.Main, ptr null }]
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
// CHECK:STDOUT: define dso_local void @_Z11pass_signedasil.carbon_thunk(ptr noundef %0, ptr noundef %1, i32 noundef %2, i64 noundef %3) #0 {
@@ -224,6 +225,13 @@ fn PassValueExpr(y: Cpp.Y) {
// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #3
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define internal void @_C__global_init.Main() #2 !dbg !48 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: store i16 poison, ptr @_Cc.Main, align 2, !dbg !49
// CHECK:STDOUT: ret void, !dbg !50
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; uselistorder directives
// CHECK:STDOUT: uselistorder ptr @llvm.lifetime.start.p0, { 7, 6, 5, 4, 3, 2, 1, 0 }
// CHECK:STDOUT:
@@ -284,6 +292,9 @@ fn PassValueExpr(y: Cpp.Y) {
// CHECK:STDOUT: !45 = !DILocation(line: 19, column: 3, scope: !31)
// CHECK:STDOUT: !46 = !DILocation(line: 20, column: 3, scope: !31)
// CHECK:STDOUT: !47 = !DILocation(line: 16, column: 1, scope: !31)
// CHECK:STDOUT: !48 = distinct !DISubprogram(name: "__global_init", linkageName: "_C__global_init.Main", scope: null, file: !6, type: !22, spFlags: DISPFlagDefinition, unit: !5)
// CHECK:STDOUT: !49 = !DILocation(line: 14, column: 1, scope: !48)
// CHECK:STDOUT: !50 = !DILocation(line: 0, scope: !48)
// CHECK:STDOUT: ; ModuleID = 'import_struct.carbon'
// CHECK:STDOUT: source_filename = "import_struct.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"