[Tests] Update swiftinterface imports Swift 6 test

Update the test for imports defaulting to internal by adding the
explicit `public` modifier on all imports and the expected warnings.
Modernized a test somehow as it can't use previously shared files.

This revealed an issue with the warning about superfluous imports on
imports of submodules. I've marked one of them as a FIXME as it will
require a fix in the diagnostic.

Author: xymus

test/ModuleInterface/imports-swift6.swift

@@ -3,23 +3,47 @@
 // REQUIRES: asserts
 
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -emit-module -o %t/empty.swiftmodule %S/../Inputs/empty.swift
-// RUN: %target-swift-frontend -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -emit-module -o %t/emptyButWithLibraryEvolution.swiftmodule %S/../Inputs/empty.swift -enable-library-evolution
+// RUN: split-file --leading-lines %s %t
+// RUN: %target-swift-frontend -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -emit-module -o %t/nonResilient.swiftmodule %t/empty.swift
+// RUN: %target-swift-frontend -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -emit-module -o %t/resilient.swiftmodule %t/empty.swift -enable-library-evolution
 
-/// Swift 6 variant.
-// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %s %S/Inputs/imports-other.swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -I %S/Inputs/imports-clang-modules/ -I %t -verify -swift-version 6
+/// Check errors.
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %t/clientWithError.swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -I %t -verify -swift-version 6
+
+/// Check Swift 6 imports printed in swiftinterface from 2 source files.
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %t/main.swift %t/main-other.swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -I %S/Inputs/imports-clang-modules/ -I %t -verify -swift-version 6
 // RUN: %target-swift-typecheck-module-from-interface(%t.swiftinterface) -I %S/Inputs/imports-clang-modules/ -I %t
 // RUN: %FileCheck -implicit-check-not BAD -check-prefix CHECK-6 %s < %t.swiftinterface
 
-@_exported import empty // expected-warning {{module 'empty' was not compiled with library evolution support; using it means binary compatibility for 'main' can't be guaranteed}}
-@_exported import emptyButWithLibraryEvolution
-import B.B2
-import func C.c // expected-warning {{scoped imports are not yet supported in module interfaces}}
+//--- empty.swift
+
+//--- main.swift
+@_exported public import resilient // expected-warning {{public import of 'resilient' was not used in public declarations or inlinable code}}
+public import B.B2 // expected-warning {{public import of 'B2' was not used in public declarations or inlinable code}}
+// expected-warning @-1 {{public import of 'B' was not used in public declarations or inlinable code}}
+// FIXME: We don't want this last warning.
+
+public import func C.c // expected-warning {{public import of 'C' was not used in public declarations or inlinable code}}
+// expected-warning @-1 {{scoped imports are not yet supported in module interfaces}}
 import D
 @_implementationOnly import Secret_BAD
 
 @_implementationOnly import NotSoSecret // expected-note {{imported as implementation-only here}}
-import NotSoSecret2 // expected-warning {{'NotSoSecret2' inconsistently imported as implementation-only}}
+public import NotSoSecret2 // expected-warning {{'NotSoSecret2' inconsistently imported as implementation-only}}
+// expected-warning @-1 {{public import of 'NotSoSecret2' was not used in public declarations or inlinable code}}
+
+//--- main-other.swift
+public import A // expected-warning {{public import of 'A' was not used in public declarations or inlinable code}}
+public import B.B3 // expected-warning {{public import of 'B3' was not used in public declarations or inlinable code}}
+// expected-warning @-1 {{public import of 'B' was not used in public declarations or inlinable code}}
+public import D // expected-warning {{public import of 'D' was not used in public declarations or inlinable code}}
+
+public import NotSoSecret // expected-warning {{'NotSoSecret' inconsistently imported as implementation-only}}
+// expected-warning @-1 {{public import of 'NotSoSecret' was not used in public declarations or inlinable code}}
+@_implementationOnly import NotSoSecret2 // expected-note {{imported as implementation-only here}}
+//--- clientWithError.swift
+@_exported public import nonResilient // expected-error {{module 'nonResilient' was not compiled with library evolution support; using it means binary compatibility for 'clientWithError' can't be guaranteed}}
+// expected-warning @-1 {{public import of 'nonResilient' was not used in public declarations or inlinable code}}
 
 // CHECK-6-NOT: import
 // CHECK-6: {{^}}public import A{{$}}
@@ -31,6 +55,5 @@ import NotSoSecret2 // expected-warning {{'NotSoSecret2' inconsistently imported
 // CHECK-6-NEXT: {{^}}public import NotSoSecret{{$}}
 // CHECK-6-NEXT: {{^}}public import NotSoSecret2{{$}}
 // CHECK-6-NEXT: {{^}}public import Swift{{$}}
-// CHECK-6-NEXT: {{^}}@_exported public import empty{{$}}
-// CHECK-6-NEXT: {{^}}@_exported public import emptyButWithLibraryEvolution{{$}}
+// CHECK-6-NEXT: {{^}}@_exported public import resilient{{$}}
 // CHECK-6-NOT: import