cmTarget: Do not enforce CMP0111 on imported INTERFACE libraries

Fix logic added by commit 359c500a24 (cmTarget: Raise error if imported
target location is not set, 2020-08-08, v3.19.0-rc1~273^2) to exclude
INTERFACE libraries from the policy.  They have no location.

Fixes: #21470

Source/cmTarget.cxx

@@ -2045,35 +2045,37 @@ std::string cmTarget::ImportedGetFullPath(
   }
 
   if (result.empty()) {
-    auto message = [&]() -> std::string {
-      std::string unset;
-      std::string configuration;
-
-      if (artifact == cmStateEnums::RuntimeBinaryArtifact) {
-        unset = "IMPORTED_LOCATION";
-      } else if (artifact == cmStateEnums::ImportLibraryArtifact) {
-        unset = "IMPORTED_IMPLIB";
-      }
-
-      if (!config.empty()) {
-        configuration = cmStrCat(" configuration \"", config, "\"");
-      }
+    if (this->GetType() != cmStateEnums::INTERFACE_LIBRARY) {
+      auto message = [&]() -> std::string {
+        std::string unset;
+        std::string configuration;
+
+        if (artifact == cmStateEnums::RuntimeBinaryArtifact) {
+          unset = "IMPORTED_LOCATION";
+        } else if (artifact == cmStateEnums::ImportLibraryArtifact) {
+          unset = "IMPORTED_IMPLIB";
+        }
 
-      return cmStrCat(unset, " not set for imported target \"",
-                      this->GetName(), "\"", configuration, ".");
-    };
+        if (!config.empty()) {
+          configuration = cmStrCat(" configuration \"", config, "\"");
+        }
 
-    switch (this->GetPolicyStatus(cmPolicies::CMP0111)) {
-      case cmPolicies::WARN:
-        impl->Makefile->IssueMessage(
-          MessageType::AUTHOR_WARNING,
-          cmPolicies::GetPolicyWarning(cmPolicies::CMP0111) + "\n" +
-            message());
-        CM_FALLTHROUGH;
-      case cmPolicies::OLD:
-        break;
-      default:
-        impl->Makefile->IssueMessage(MessageType::FATAL_ERROR, message());
+        return cmStrCat(unset, " not set for imported target \"",
+                        this->GetName(), "\"", configuration, ".");
+      };
+
+      switch (this->GetPolicyStatus(cmPolicies::CMP0111)) {
+        case cmPolicies::WARN:
+          impl->Makefile->IssueMessage(
+            MessageType::AUTHOR_WARNING,
+            cmPolicies::GetPolicyWarning(cmPolicies::CMP0111) + "\n" +
+              message());
+          CM_FALLTHROUGH;
+        case cmPolicies::OLD:
+          break;
+        default:
+          impl->Makefile->IssueMessage(MessageType::FATAL_ERROR, message());
+      }
     }
 
     result = cmStrCat(this->GetName(), "-NOTFOUND");

Tests/RunCMake/CMP0111/CMP0111-Common.cmake

@@ -4,6 +4,7 @@ set(CMAKE_IMPORT_LIBRARY_SUFFIX "placeholder")
 add_library(unknown_lib UNKNOWN IMPORTED)
 add_library(static_lib STATIC IMPORTED)
 add_library(shared_lib SHARED IMPORTED)
+add_library(interface_lib INTERFACE IMPORTED)
 
-add_executable(executable main.cpp)
-target_link_libraries(executable unknown_lib static_lib shared_lib)
+add_library(module MODULE module.cpp)
+target_link_libraries(module unknown_lib static_lib shared_lib interface_lib)

Tests/RunCMake/CMP0111/main.cpp

@@ -1,3 +0,0 @@
-int main()
-{
-}

Tests/RunCMake/CMP0111/module.cpp

@@ -0,0 +1,4 @@
+int module()
+{
+  return 0;
+}