Better support of pre-2.7 ruby

configure.ac

@@ -27,6 +27,17 @@ if test -z "$RUBY"; then
   AC_CHECK_PROG(RUBY,[ruby],[ruby],[no])
   test "$RUBY" == "no" && AC_MSG_ERROR([Required program 'ruby' not found.])
 fi
+# iprof needs Ruby >= 2.7. It's a runtime dependency, but we assume people use
+# the same ruby version at compile and runtime. Will also be used to potentially
+# update other parts of the project.
+RUBY_MIN_VERSION=2.7.0
+AC_SUBST([RUBY_MIN_VERSION])
+AC_MSG_CHECKING([for ruby >= $RUBY_MIN_VERSION])
+RUBY_VERSION_FOUND=`$RUBY -e 'print RUBY_VERSION'`
+AX_COMPARE_VERSION([$RUBY_VERSION_FOUND], [ge], [$RUBY_MIN_VERSION],
+  [AC_MSG_RESULT([yes])],
+  [AC_MSG_RESULT([no])
+   AC_MSG_ERROR([ruby version $RUBY_VERSION_FOUND is too old, need >= $RUBY_MIN_VERSION])])
 if test -z "$ERB"; then
   AC_CHECK_PROG(ERB,[erb],[erb],[no])
   test "$ERB" == "no" && AC_MSG_ERROR([Required program 'erb' not found.])
@@ -155,6 +166,7 @@ AC_CONFIG_FILES([backends/mpi/tracer_mpi.sh], [chmod +x backends/mpi/tracer_mpi.
 AC_CONFIG_FILES([backends/itt/tracer_itt.sh], [chmod +x backends/itt/tracer_itt.sh])
 AC_CONFIG_FILES([utils/babeltrace_thapi], [chmod +x utils/babeltrace_thapi])
 AC_CONFIG_FILES([xprof/xprof.rb], [chmod +x xprof/xprof.rb])
+AC_CONFIG_FILES([xprof/iprof:xprof/xprof_wrapper.rb.in], [chmod +x xprof/iprof])
 AC_CONFIG_FILES([thapi.pc])
 
 AC_OUTPUT

integration_tests/old_ruby_frontend.bats

@@ -0,0 +1,34 @@
+bats_require_minimum_version 1.5.0
+
+# The `iprof` launcher must stay parseable by an old Ruby (the system default on
+# some machines) so that, on a too-old interpreter, it prints a friendly version
+# message instead of a raw SyntaxError. All modern-syntax logic lives in the
+# required `xprof.rb`, which is only parsed after the version gate passes.
+
+setup() {
+  # ruby CLI need a path
+  iprof_path=$(command -v iprof)
+
+  # Single source of truth: read the minimal ruby version baked into iprof itself
+  # (configure.ac may not be present, e.g. CI only ships the install tree). The
+  # value keeps its quotes, so it drops straight into the ruby below.
+  min_version=$(awk '/^THAPI_RUBY_MINIMAL_VERSION/ {print $3}' "${iprof_path}")
+
+  # The ruby to test against. Defaults to `ruby`; point THAPI_OLD_RUBY at an old
+  # interpreter to exercise this on a machine whose default ruby is recent.
+  old_ruby="${THAPI_OLD_RUBY:-ruby}"
+  if "${old_ruby}" -e "exit(Gem::Version.new(RUBY_VERSION) >= Gem::Version.new(${min_version}))"; then
+    skip "${old_ruby} is >= ${min_version}; set THAPI_OLD_RUBY to an older ruby to run this test"
+  fi
+}
+
+@test "frontend_parses_under_old_ruby" {
+  run -0 "${old_ruby}" -c "${iprof_path}"
+}
+
+@test "frontend_prints_friendly_message_under_old_ruby" {
+  run ! "${old_ruby}" "${iprof_path}" --help
+  [[ "${output}" == *"too old"* ]]
+  [[ "${output}" != *"SyntaxError"* ]]
+  [[ "${output}" != *"unexpected"* ]]
+}

xprof/Makefile.am

@@ -13,16 +13,20 @@ bin_SCRIPTS = \
 	iprof \
 	sync_daemon_fs
 
+# `iprof` is the old-Ruby-safe wrapper, generated from xprof_wrapper.rb.in by
+# configure (see configure.ac). It requires xprof.rb (the implementation) from
+# DATADIR at runtime, the same place as optparse_thapi.rb and version (see
+# utils/Makefile.am).
+data_DATA = \
+	xprof.rb
+
 if FOUND_MPI
   bin_SCRIPTS += sync_daemon_mpi
 endif
 
 sync_daemon_mpi: $(srcdir)/sync_daemon_mpi.cpp
 	$(MPICXX) $(CXXFLAGS) $(AM_CXXFLAGS) -I$(top_srcdir)/utils/include $< -o $@
 
-iprof: xprof.rb
-	cp xprof.rb $@
-
 xprof_utils.hpp: $(top_srcdir)/utils/xprof_utils.hpp
 	cp $< $@
 
@@ -227,7 +231,6 @@ EXTRA_DIST = \
 	sync_daemon_fs
 
 CLEANFILES = \
-	iprof \
 	xprof_utils.hpp \
 	perfetto_pruned.pb.h \
 	perfetto_pruned.pb.cc \

xprof/sync_daemon_fs

@@ -1,8 +1,9 @@
 #!/usr/bin/env ruby
 
-# Cannot use require_relative as iprof is not a rb file
-# Load MPITopo and related helpers
-load(File.join(__dir__, 'iprof'))
+# Load MPITopo and related helpers from the implementation (installed in
+# ../share), not the iprof wrapper, which would set $thapi_launch and run the
+# whole program instead of just defining helpers.
+require_relative File.join('..', 'share', 'xprof')
 
 require 'open3'
 require 'fileutils'
@@ -66,12 +67,11 @@ until msg == SyncDaemon::MSG_FINISH
   raise 'sync_daemon_fs: parent closed socket without sending FINISH' if msg.empty?
 
   case msg
-  when SyncDaemon::MSG_INIT then nil
+  when SyncDaemon::MSG_INIT, SyncDaemon::MSG_FINISH then nil
   when SyncDaemon::MSG_LOCAL_BARRIER
     local_barrier(local_barrier_count.to_s)
     local_barrier_count += 1
   when SyncDaemon::MSG_GLOBAL_BARRIER then global_barrier(global_handle)
-  when SyncDaemon::MSG_FINISH         then nil
   else
     warn("sync_daemon_fs: unknown message '#{msg}'")
     exit(1)

xprof/xprof.rb.in

@@ -1,11 +1,6 @@
 #!/usr/bin/env ruby
 
-# 2.7 for Lazy in Enumerable. 2.7 was released 25 Dec 2019
-THAPI_RUBY_MINIMAL_VERSION = '2.7.0'
-if Gem::Version.new(RUBY_VERSION) < Gem::Version.new(THAPI_RUBY_MINIMAL_VERSION)
-  warn("Your ruby version #{RUBY_VERSION} is too old. #{THAPI_RUBY_MINIMAL_VERSION} or newer required")
-  exit(1)
-end
+# This file doesn't do any ruby version check. All the check are done in `iprof`.
 
 # We Cannot use "@ .. @" for libdir, bindir, and datarootdir
 # as they will appear as bash "${exec_prefix}/lib"
@@ -1007,8 +1002,9 @@ def last_trace_saved
   Dir[File.join(thapi_trace_home, 'thapi*')].max_by { |f| File.mtime(f) }
 end
 
-# Avoid load problem
-if __FILE__ == $PROGRAM_NAME
+# Run when launched through the `iprof` wrapper (which sets $thapi_launch before
+# requiring this file) or when executed directly.
+if $thapi_launch || __FILE__ == $PROGRAM_NAME
   parser = OptionParserWithDefaultAndValidation.new
 
   parser.banner = "Usage: #{File.basename($PROGRAM_NAME)} [options] [--] [command]"

xprof/xprof_wrapper.rb.in

@@ -0,0 +1,18 @@
+#!/usr/bin/env ruby
+
+# User-facing `iprof` launcher. It MUST stay parseable by old Ruby: Ruby parses
+# the whole file before running any of it, so modern syntax here (endless ranges,
+# pattern matching, ...) would raise a raw SyntaxError before the version check
+# below could run. All real logic lives in xprof.rb, required only after the check
+# passes, so users on an old Ruby get the friendly message below instead.
+
+# Named constant (not inlined) so bats can grep the minimal version out of iprof.
+THAPI_RUBY_MINIMAL_VERSION = '@RUBY_MIN_VERSION@'
+if Gem::Version.new(RUBY_VERSION) < Gem::Version.new(THAPI_RUBY_MINIMAL_VERSION)
+  warn("Your ruby version #{RUBY_VERSION} is too old. #{THAPI_RUBY_MINIMAL_VERSION} or newer required")
+  exit(1)
+end
+
+$LOAD_PATH.unshift(File.join('@prefix@', 'share'))
+$thapi_launch = true
+require 'xprof'