debug: initial global debug flag support (#24285)

The developer can export environment variables that
are seen by the compiler wrapper to then add the flags

lib/spack/docs/developer_guide.rst

@@ -785,6 +785,38 @@ Unit tests
 Unit testing
 ------------
 
+---------------------
+Developer environment
+---------------------
+
+.. warning::
+
+    This is an experimental feature. It is expected to change and you should
+    not use it in a production environment.
+
+
+When installing a package, we currently have support to export environment
+variables to specify adding debug flags to the build. By default, a package
+install will build without any debug flag. However, if you want to add them,
+you can export:
+
+.. code-block:: console
+
+   export SPACK_ADD_DEBUG_FLAGS=true
+   spack install zlib
+
+
+If you want to add custom flags, you should export an additional variable:
+
+.. code-block:: console
+
+   export SPACK_ADD_DEBUG_FLAGS=true
+   export SPACK_DEBUG_FLAGS="-g"
+   spack install zlib
+
+These environment variables will eventually be integrated into spack so
+they are set from the command line.
+
 ------------------
 Developer commands
 ------------------

lib/spack/env/cc

@@ -40,6 +40,14 @@ parameters=(
     SPACK_SYSTEM_DIRS
 )
 
+# Optional parameters that aren't required to be set
+
+# Boolean (true/false/custom) if we want to add debug flags
+# SPACK_ADD_DEBUG_FLAGS
+
+# If a custom flag is requested, it will be defined
+# SPACK_DEBUG_FLAGS
+
 # The compiler input variables are checked for sanity later:
 #   SPACK_CC, SPACK_CXX, SPACK_F77, SPACK_FC
 # The default compiler flags are passed from these variables:
@@ -87,6 +95,25 @@ for param in "${parameters[@]}"; do
     fi
 done
 
+# Check if optional parameters are defined
+# If we aren't asking for debug flags, don't add them
+if [[ -z ${SPACK_ADD_DEBUG_FLAGS+x} ]]; then
+    SPACK_ADD_DEBUG_FLAGS="false"
+fi
+
+# SPACK_ADD_DEBUG_FLAGS must be true/false/custom
+is_valid="false"
+for param in "true" "false" "custom"; do
+  if [ "$param" == "$SPACK_ADD_DEBUG_FLAGS" ];  then
+      is_valid="true"
+  fi
+done
+
+# Exit with error if we are given an incorrect value
+if [ "$is_valid" == "false" ]; then
+    die "SPACK_ADD_DEBUG_FLAGS, if defined, must be one of 'true' 'false' or 'custom'"
+fi
+
 # Figure out the type of compiler, the language, and the mode so that
 # the compiler script knows what to do.
 #
@@ -106,30 +133,35 @@ comp="CC"
 case "$command" in
     cpp)
         mode=cpp
+        debug_flags="-g"
         ;;
     cc|c89|c99|gcc|clang|armclang|icc|icx|pgcc|nvc|xlc|xlc_r|fcc)
         command="$SPACK_CC"
         language="C"
         comp="CC"
         lang_flags=C
+        debug_flags="-g"
         ;;
     c++|CC|g++|clang++|armclang++|icpc|icpx|pgc++|nvc++|xlc++|xlc++_r|FCC)
         command="$SPACK_CXX"
         language="C++"
         comp="CXX"
         lang_flags=CXX
+        debug_flags="-g"
         ;;
     ftn|f90|fc|f95|gfortran|flang|armflang|ifort|ifx|pgfortran|nvfortran|xlf90|xlf90_r|nagfor|frt)
         command="$SPACK_FC"
         language="Fortran 90"
         comp="FC"
         lang_flags=F
+        debug_flags="-g"
         ;;
     f77|xlf|xlf_r|pgf77)
         command="$SPACK_F77"
         language="Fortran 77"
         comp="F77"
         lang_flags=F
+        debug_flags="-g"
         ;;
     ld)
         mode=ld
@@ -415,6 +447,16 @@ done
 #
 flags=()
 
+# Add debug flags
+if [ "${SPACK_ADD_DEBUG_FLAGS}" == "true" ]; then
+    flags=("${flags[@]}" "${debug_flags}")
+
+# If a custom flag is requested, derive from environment
+elif [ "$SPACK_ADD_DEBUG_FLAGS" == "custom" ]; then
+    IFS=' ' read -ra SPACK_DEBUG_FLAGS <<< "$SPACK_DEBUG_FLAGS"
+    flags=("${flags[@]}" "${SPACK_DEBUG_FLAGS[@]}")
+fi
+
 # Fortran flags come before CPPFLAGS
 case "$mode" in
     cc|ccld)