find_library: Infer library prefix and suffix when in script mode

This aligns `find_library` with the documentation that states it
can be called from script mode. This is done by infering the
proper prefix and suffix values when `find_library` is called
when the `CMAKE_FIND_LIBRARY*` are not set. This also means that
`find_library` won't produce obscure error messages about unset
definitions.

Fixes: #22027

Source/cmFindLibraryCommand.cxx

@@ -259,6 +259,34 @@ struct cmFindLibraryHelper
   };
 };
 
+namespace {
+
+std::string const& get_prefixes(cmMakefile* mf)
+{
+#ifdef _WIN32
+  static std::string defaultPrefix = ";lib";
+#else
+  static std::string defaultPrefix = "lib";
+#endif
+  cmProp prefixProp = mf->GetDefinition("CMAKE_FIND_LIBRARY_PREFIXES");
+  return (prefixProp) ? *prefixProp : defaultPrefix;
+}
+
+std::string const& get_suffixes(cmMakefile* mf)
+{
+#ifdef _WIN32
+  static std::string defaultSuffix = ".lib;.dll.a;.a";
+#elif defined(__APPLE__)
+  static std::string defaultSuffix = ".tbd;.dylib;.so;.a";
+#elif defined(__hpux)
+  static std::string defaultSuffix = ".sl;.so;.a";
+#else
+  static std::string defaultSuffix = ".so;.a";
+#endif
+  cmProp suffixProp = mf->GetDefinition("CMAKE_FIND_LIBRARY_SUFFIXES");
+  return (suffixProp) ? *suffixProp : defaultSuffix;
+}
+}
 cmFindLibraryHelper::cmFindLibraryHelper(std::string debugName, cmMakefile* mf,
                                          cmFindBase const* base)
   : Makefile(mf)
@@ -268,10 +296,9 @@ cmFindLibraryHelper::cmFindLibraryHelper(std::string debugName, cmMakefile* mf,
   this->GG = this->Makefile->GetGlobalGenerator();
 
   // Collect the list of library name prefixes/suffixes to try.
-  std::string const& prefixes_list =
-    this->Makefile->GetRequiredDefinition("CMAKE_FIND_LIBRARY_PREFIXES");
-  std::string const& suffixes_list =
-    this->Makefile->GetRequiredDefinition("CMAKE_FIND_LIBRARY_SUFFIXES");
+  std::string const& prefixes_list = get_prefixes(this->Makefile);
+  std::string const& suffixes_list = get_suffixes(this->Makefile);
+
   cmExpandList(prefixes_list, this->Prefixes, true);
   cmExpandList(suffixes_list, this->Suffixes, true);
   this->RegexFromList(this->PrefixRegexStr, this->Prefixes);

Tests/RunCMake/find_library/FromScriptMode-stderr-darwin.txt

@@ -0,0 +1,4 @@
+.*find_library considered the following locations.*
+.*\(lib\)library_no_exist\(\\.tbd\|\\.dylib\|\\.so\|\\.a\).*
+.*The item was found at.*
+.*lib/libcreated.a.*

Tests/RunCMake/find_library/FromScriptMode-stderr-windows.txt

@@ -0,0 +1,4 @@
+.*find_library considered the following locations.*
+.*\(\|lib\)library_no_exist\(\\.lib\|\\.dll\\.a\|\\.a\).*
+.*The item was found at.*
+.*lib/libcreated.a.*

Tests/RunCMake/find_library/FromScriptMode-stderr.txt

@@ -0,0 +1,4 @@
+.*find_library considered the following locations.*
+.*\(lib\)library_no_exist\(\\.so\|\\.a\).*
+.*The item was found at.*
+.*lib/libcreated.a.*

Tests/RunCMake/find_library/FromScriptMode.cmake

@@ -0,0 +1,15 @@
+
+if(TEMP_DIR)
+  file(REMOVE_RECURSE "${TEMP_DIR}")
+  file(MAKE_DIRECTORY "${TEMP_DIR}")
+  file(MAKE_DIRECTORY "${TEMP_DIR}/lib")
+  file(WRITE "${TEMP_DIR}/lib/libcreated.a" "created")
+endif()
+
+set(CMAKE_FIND_DEBUG_MODE 1)
+find_library(CREATED_LIBRARY NAMES library_no_exist)
+
+set(CMAKE_PREFIX_PATH "${TEMP_DIR}")
+find_library(CREATED_LIBRARY NAMES created)
+message(STATUS "CREATED_LIBRARY='${CREATED_LIBRARY}'")
+set(CMAKE_FIND_DEBUG_MODE 0)

Tests/RunCMake/find_library/RunCMakeTest.cmake

@@ -10,3 +10,5 @@ endif()
 run_cmake(PrefixInPATH)
 run_cmake(Required)
 run_cmake(NO_CACHE)
+
+run_cmake_script(FromScriptMode "-DTEMP_DIR=${RunCMake_BINARY_DIR}/FromScriptMode-temp")