[cmake] Remove compression_default option

In theory, it provides the means to change the default compression
algorithm. This used to work when TFile defaulted to compress=1, only
specifying the compression level, but commit e9c4b2e in 2018 changed
the default to 101, including the compression algorithm. Moreover, lzma
wasn't implemented so the option didn't live up to its documentation.

Author: hahnjo

README/ReleaseNotes/v640/index.md

@@ -69,6 +69,7 @@ The following people have contributed to this new version:
      multiGraph->Add(static_cast<TGraph*>(gr->Clone()));
   }
   ```
+* The `compression_default` build option was removed. It was supposed to change the default compression algorithm, but didn't actually work with the default parameters of `TFile`.
 
 ## Build System
 

cmake/modules/RootBuildOptions.cmake

@@ -202,16 +202,6 @@ if(all AND minimal)
   message(FATAL_ERROR "The 'all' and 'minimal' options are mutually exclusive")
 endif()
 
-#--- Compression algorithms in ROOT-------------------------------------------------------------
-set(compression_default "zlib" CACHE STRING "Default compression algorithm (zlib (default), lz4, zstd or lzma)")
-string(TOLOWER "${compression_default}" compression_default)
-if("${compression_default}" MATCHES "zlib|lz4|lzma|zstd")
-  message(STATUS "ROOT default compression algorithm: ${compression_default}")
-else()
-  message(FATAL_ERROR "Unsupported compression algorithm: ${compression_default}\n"
-    "Known values are zlib, lzma, lz4, zstd (case-insensitive).")
-endif()
-
 #--- The 'all' option switches ON major options---------------------------------------------------
 if(all)
  set(arrow_defvalue ON)
@@ -381,8 +371,9 @@ endif()
 
 #---Removed options------------------------------------------------------------
 # Please notify SPI when adding to this list
-foreach(opt afdsmgrd afs alien bonjour builtin_afterimage builtin_davix castor chirp cxx11 cxx14 cxx17
-        cxxmodules exceptions geocad gfal glite globus gsl_shared hdfs html ios jemalloc krb5
+foreach(opt afdsmgrd afs alien bonjour builtin_afterimage builtin_davix castor chirp
+        compression_default cxx11 cxx14 cxx17 cxxmodules exceptions
+        geocad gfal glite globus gsl_shared hdfs html ios jemalloc krb5
         ldap memstat minuit2 monalisa oracle proof pyroot-python2 pyroot_legacy
         pythia6 pythia6_nolink python qt qtgsi qt5web rfio ruby sapdb srp table
         tcmalloc vmc xproofd mysql odbc pgsql)

cmake/modules/RootConfiguration.cmake

@@ -396,12 +396,6 @@ else()
   set(hasroot7 undef)
 endif()
 
-set(uselz4 undef)
-set(usezlib undef)
-set(uselzma undef)
-set(usezstd undef)
-set(use${compression_default} define)
-
 if(ZLIB_NG)
   set(usezlibng define)
 else()

config/RConfigure.in

@@ -53,10 +53,6 @@
 #@use_less_includes@ R__LESS_INCLUDES /**/
 #define R__HARDWARE_INTERFERENCE_SIZE @hardwareinterferencesize@ /*Determined at CMake configure to be stable across all TUs*/
 
-#@uselz4@ R__HAS_DEFAULT_LZ4  /**/
-#@usezlib@ R__HAS_DEFAULT_ZLIB  /**/
-#@uselzma@ R__HAS_DEFAULT_LZMA  /**/
-#@usezstd@ R__HAS_DEFAULT_ZSTD  /**/
 #@usezlibng@ R__HAS_ZLIB_NG /**/
 
 #@hastmvacpu@ R__HAS_TMVACPU /**/

core/zip/src/RZip.cxx

@@ -48,13 +48,7 @@ static void R__unzipZLIB(int *srcsize, const unsigned char *src, int *tgtsize, u
   is done.  LZ4 typically has the worst compression ratios, but much faster decompression
   speeds - sometimes by an order of magnitude.
 */
-#ifdef R__HAS_DEFAULT_ZSTD
-ROOT::RCompressionSetting::EAlgorithm::EValues R__ZipMode = ROOT::RCompressionSetting::EAlgorithm::EValues::kZSTD;
-#elif defined(R__HAS_DEFAULT_LZ4)
-ROOT::RCompressionSetting::EAlgorithm::EValues R__ZipMode = ROOT::RCompressionSetting::EAlgorithm::EValues::kLZ4;
-#else
 ROOT::RCompressionSetting::EAlgorithm::EValues R__ZipMode = ROOT::RCompressionSetting::EAlgorithm::EValues::kZLIB;
-#endif
 
 /* ===========================================================================
    Function to set the ZipMode