cmake: Fix "make flash" & "ninja flash" targets

As reported on forum.

Requires a small CMake wrapper script to pick
up environment variables at flashing time.

components/esptool_py/project_include.cmake

@@ -43,9 +43,14 @@ add_custom_target(app ALL DEPENDS "${PROJECT_NAME}.bin")
 #
 function(esptool_py_custom_target target_name flasher_filename dependencies)
     add_custom_target(${target_name} DEPENDS ${dependencies}
-        COMMAND ${ESPTOOLPY} -p ${CONFIG_ESPTOOLPY_PORT} -b ${CONFIG_ESPTOOLPY_BAUD}
-        write_flash @flash_${flasher_filename}_args
-        WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
+        COMMAND ${CMAKE_COMMAND}
+        -D IDF_PATH="${IDF_PATH}"
+        -D ESPTOOLPY="${ESPTOOLPY}"
+        -D ESPTOOL_ARGS="write_flash;@flash_${flasher_filename}_args"
+        -D ESPTOOL_WORKING_DIR="${CMAKE_CURRENT_BINARY_DIR}"
+        -P run_esptool.cmake
+        WORKING_DIRECTORY ${CMAKE_CURRENT_LIST_DIR}
+        USES_TERMINAL
         )
 endfunction()
 

components/esptool_py/run_esptool.cmake

@@ -0,0 +1,45 @@
+# A CMake script to run esptool commands from within ninja or make
+# or another cmake-based build runner
+#
+# (Needed to expand environment variables, for backwards compatibility.)
+#
+# It is recommended to NOT USE this CMake script if you have the option of
+# running esptool.py directly. This script exists only for use inside CMake builds.
+#
+cmake_minimum_required(VERSION 3.5)
+
+if(NOT IDF_PATH OR NOT ESPTOOLPY OR NOT ESPTOOL_ARGS OR NOT ESPTOOL_WORKING_DIR)
+    message(FATAL_ERROR "IDF_PATH, ESPTOOLPY, ESPTOOL_ARGS, and ESPTOOL_WORKING_DIR must "
+        "be specified on the CMake command line. For direct esptool execution, it is "
+        "strongly recommended to run esptool.py directly.")
+endif()
+
+# Note: we can't expand these environment variables in the main IDF CMake build,
+# because we want to expand them at flashing time not at CMake runtime (so they can change
+# without needing a CMake re-run)
+if(NOT ENV{ESPPORT})
+    message("Note: esptool.py will search for a serial port. To specify a port, set the ESPPORT environment variable.")
+else()
+    set(port_arg "-p $ENV{ESPPORT}")
+endif()
+
+set(ESPBAUD $ENV{ESPBAUD})
+if(NOT ESPBAUD)
+    message("Note: Using default baud rate 460800. To modify, set ESPBAUD environment variable.")
+    set(ESPBAUD 460800)
+endif()
+
+include("${IDF_PATH}/tools/cmake/utilities.cmake")
+
+set(cmd "${ESPTOOLPY} ${port_arg} -b ${ESPBAUD} ${ESPTOOL_ARGS}")
+spaces2list(cmd)
+
+execute_process(COMMAND ${cmd}
+    WORKING_DIRECTORY "${ESPTOOL_WORKING_DIR}"
+    RESULT_VARIABLE result
+    )
+
+if(${result})
+    # No way to have CMake silently fail, unfortunately
+    message(FATAL_ERROR "esptool.py failed")
+endif()