new omp_set_nested_linter for C (#6347)

* Add a linter for calls to omp_set_num_threads

* simplify, comment

* refactor

* new omp_set_nested_linter

* #define in myomp.h is not needed since macro is not used

.ci/linters/c/omp_set_nested_linter.R

@@ -0,0 +1,11 @@
+# Ensure no calls to omp_set_nested() as
+#   i) it's hard to fully honor OMP_THREAD_LIMIT as required by CRAN, and
+#   ii) a simpler non-nested approach is always preferable if possible, as has been the case so far
+omp_set_nested_linter = function(c_obj) {
+  idx = grep("omp_set_nested", c_obj$lines, fixed=TRUE)
+  if (!length(idx)) return()
+  stop(sprintf(
+    "In %s, found omp_set_nested() usage, please reconsider:\n%s",
+    c_obj$path, paste0("  ", format(idx), ":", c_obj$lines[idx], collapse = "\n")
+  ))
+}

.dev/CRAN_Release.cmd

@@ -54,11 +54,6 @@ grep -RI --exclude-dir=".git" --exclude="*.md" --exclude="*~" --color='auto' -P
 # Unicode is now ok. This unicode in tests.Rraw is passing on CRAN.
 grep -RI --exclude-dir=".git" --exclude="*.md" --exclude="*~" --color='auto' -n "[\]u[0-9]" ./
 
-
-# Ensure no calls to omp_set_nested() as i) it's hard to fully honor OMP_THREAD_LIMIT as required by CRAN, and
-#                                        ii) a simpler non-nested approach is always preferable if possible, as has been the case so far
-grep omp_set_nested ./src/*.c
-
 # Ensure no calls to omp_get_max_threads() also since access should be via getDTthreads()
 grep --exclude="./src/openmp-utils.c" omp_get_max_threads ./src/*
 

src/myomp.h

@@ -23,7 +23,6 @@
   #define omp_get_max_threads()  1
   #define omp_get_thread_limit() 1
   #define omp_get_num_procs()    1
-  #define omp_set_nested(a)   // empty statement to remove the call
   #define omp_get_wtime()        0
   #define MY_OPENMP              0
 #endif