add example demonstrating advanced PlatformIO environment inheritance

Adds a self-documented example demonstrating how a user can inherit from a core WLED configuration and add their own values without needing to copy all of the upstream values manually. This new method simplifies configuration maintenance for the users.

Author: Arcitec

platformio_override.sample.ini

@@ -536,3 +536,36 @@ extends = env:esp32dev
 build_flags = ${env:esp32dev.build_flags} -D USERMOD_RF433
 lib_deps = ${env:esp32dev.lib_deps}
   sui77/rc-switch @ 2.6.4
+
+# ------------------------------------------------------------------------------
+# Advanced example: Inheriting all settings from an upstream "base" config, and
+# adding/overriding specific build flags, which is useful if you want to base
+# your environment on a stable core env but just override certain WLED defaults.
+# ------------------------------------------------------------------------------
+
+[env:esp32_eth_custom]
+;; Inherit all settings from upstream config. We can then override specific settings.
+;; WARNING: The upstream environment's name, such as "esp32_eth" in this example,
+;; must also be specified in the other inherited settings (see example below).
+extends = env:esp32_eth
+
+;; Remove conflicting upstream flags to fix compiler "variable redefined" warnings.
+;; WARNING: Must specify the EXACT upstream "build_flags" flag VALUES to unset;
+;; because if we don't specify any value then it unsets ALL instances of the
+;; flag, meaning that it would erase our new values too.
+;; NOTE: If the upstream values are ever changed, the compiler will encounter
+;; duplicate values and complain about "variable redefined" again, meaning that
+;; these values will simply need to be revised. So maintenance is safe and easy.
+build_unflags = ${env:esp32_eth.build_unflags}
+  ;; Unset the old, conflicting flag values:
+  -D WLED_RELEASE_NAME=\"ESP32_Ethernet\"
+  -D RLYPIN=-1
+
+;; Inherit all upstream flags and then overwrite/append with some custom values.
+;; NOTE: You can add/modify ANY of the WLED build-time variables here (it doesn't
+;; have to be values that were in the original upstream config).
+build_flags = ${env:esp32_eth.build_flags}
+  ;; Set/add your new flag values:
+  -D WLED_RELEASE_NAME=\"ESP32_Ethernet_Custom\"
+  -D RLYPIN=24
+