From 95b5df8646fa2b02c5eba175570f83fc6e2ece55 Mon Sep 17 00:00:00 2001
From: Brad King <brad.king@kitware.com>
Date: Wed, 22 Jul 2020 10:45:33 -0400
Subject: cmGeneratorTarget: Skip computing languages for custom targets

Targets created by `add_custom_target` do not compile any sources
and therefore have no languages.
---
 Source/cmGeneratorTarget.cxx | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index beafdea..554a954 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -7013,6 +7013,11 @@ std::string cmGeneratorTarget::GetDeprecation() const
 void cmGeneratorTarget::GetLanguages(std::set<std::string>& languages,
                                      const std::string& config) const
 {
+  // Targets that do not compile anything have no languages.
+  if (!this->CanCompileSources()) {
+    return;
+  }
+
   std::vector<cmSourceFile*> sourceFiles;
   this->GetSourceFiles(sourceFiles, config);
   for (cmSourceFile* src : sourceFiles) {
-- 
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