Genex: Optimize usage requirement TARGET_PROPERTY recursion

In large projects the generation process spends a lot of time evaluating
usage requirements through transitive interface properties on targets.
This can be seen in a contrived example with deep dependencies:

    set(prev "")
    foreach(i RANGE 1 500)
      add_library(a${i} a.c)
      target_compile_definitions(a${i} PUBLIC A${i})
      target_link_libraries(a${i} PUBLIC ${prev})
      set(prev a${i})
    endforeach()

For each usage requirement (such as `INTERFACE_COMPILE_DEFINITIONS` or
`INTERFACE_INCLUDE_DIRECTORIES`), the value of the generator expression
`$<TARGET_PROPERTY:target,prop>` includes the values of the same
property from the transitive closure of link libraries of the target.

Previously we computed this by constructing a generator expression
string like `$<TARGET_PROPERTY:lib,INTERFACE_COMPILE_DEFINITIONS>` and
recursively evaluating it with the generator expression engine.  Avoid
the string construction and parsing by creating and using a dedicated
evaluation method `cmGeneratorTarget::EvaluateInterfaceProperty` that
looks up the properties directly.

Issue: #18964, #18965

1 files changed, 7 insertions, 0 deletions

diff --git a/Source/cmGeneratorTarget.h b/Source/cmGeneratorTarget.h
index e86535d..b875c40 100644
--- a/Source/cmGeneratorTarget.h
+++ b/Source/cmGeneratorTarget.h
@@ -25,6 +25,9 @@ class cmMakefile;
 class cmSourceFile;
 class cmTarget;
 
+struct cmGeneratorExpressionContext;
+struct cmGeneratorExpressionDAGChecker;
+
 class cmGeneratorTarget
 {
 public:
@@ -674,6 +677,10 @@ public:
 
   class TargetPropertyEntry;
 
+  std::string EvaluateInterfaceProperty(
+    std::string const& prop, cmGeneratorExpressionContext* context,
+    cmGeneratorExpressionDAGChecker* dagCheckerParent) const;
+
   bool HaveInstallTreeRPATH(const std::string& config) const;
 
   bool GetBuildRPATH(const std::string& config, std::string& rpath) const;