pio: even shorter suffix for .ipp files

remove .cpp from the resulting suffix, since .ipp already implies it is c++
update comments once again

code/scripts/espurna_utils/build.py

@@ -76,35 +76,27 @@ def app_add_target_build_and_copy(env):
     env.Alias("build-and-copy", target)
 
 
-# TODO: *could* be a Builder object, just the same it will detect targets via src_suffix & suffix properties
-#       but, notice that:
-#       - constantly re-generating files in $project_dir only useful in development, as we need already
-#         'compiled' .re.cpp.ipp in the source at commit time
-#       - .cpp.re.ipp <-> .re dependency will be injected into the scons database of the *environment*,
-#         which may accidentally cause a rebuild when using 2 envs at the same time
-#       - .cpp file `#include`ing the .ipp file may be built before the file is actually generated by the re2c
-#         (or, it may happen in a parallel job)
-#         scons has a C source scanner that is tracking `#include` directives. but, file may *already* exist before the
-#         scanning phase even starts and it may be assumed something static during the build
-#         (since most include directives are for the system, sdk, and the build-tree headers)
+# NOTICE that .re <-> .re.ipp dependency is tricky, b/c we want these to exist *before* any source is built
+# (or, attempted to be built. `projenv` does not exist yet, and so there are no dependecies generated)
 
 
 def app_add_target_build_re2c(env):
     from SCons.Script import COMMAND_LINE_TARGETS
 
-    targets = [
-        env.File(target) for target in COMMAND_LINE_TARGETS if ".re.cpp.ipp" in target
-    ]
-    cmd = "re2c --no-generation-date --case-ranges -W -Werror -o {} {}"
+    targets = []
+
+    for target in COMMAND_LINE_TARGETS:
+        if target.endswith(".re.ipp"):
+            targets.append(target)
+
     if targets:
-        sources = [
-            target.File("{}".format(target.name.replace(".cpp.ipp", "")))
-            for target in targets
-        ]
-        for target, source in zip(targets, sources):
-            env.Execute(
-                env.VerboseAction(
-                    cmd.format(target, source), "Generating {}".format(target.name)
-                )
+        action = env.VerboseAction(
+            "re2c --no-generation-date --case-ranges -W -Werror -o $TARGET $SOURCE",
+            "Generating $TARGET",
+        )
+
+        for target in targets:
+            action(
+                [env.File(target)], [env.File(target.replace(".re.ipp", ".re"))], env
             )
         env.Exit(0)