Moved the BOARDS_TXT section and stop if BOARDS_TXT is not a file.

The section of Arduino.mk that calculates BOARDS_TXT was moved to just
before the point where it gets used for the first time (a call to
PARSE_BOARD). An error gets generated if BOARDS_TXT is not pointing to a
valid file, directly after the BOARDS_TXT calculation.

In addition, the PARSE_BOARD macro will now be bypassed if the
BOARDS_TXT variable points to a non-existing file. If a user makefile
uses PARSE_BOARD before including Arduino.mk, and the BOARDS_TXT is
wrong, the error will only be caught in the Arduino.mk file, which is
probably acceptable.

Author: wingunder

Arduino.mk

@@ -388,6 +388,55 @@ endif
 ########################################################################
 # Arduino and system paths
 
+# Third party hardware and core like ATtiny or ATmega 16
+ifdef ALTERNATE_CORE
+    $(call show_config_variable,ALTERNATE_CORE,[USER])
+
+    ifndef ALTERNATE_CORE_PATH
+        ALTERNATE_CORE_PATH = $(ARDUINO_SKETCHBOOK)/hardware/$(ALTERNATE_CORE)/$(ARCHITECTURE)
+    endif
+endif
+
+ifdef ALTERNATE_CORE_PATH
+
+    ifdef ALTERNATE_CORE
+        $(call show_config_variable,ALTERNATE_CORE_PATH,[COMPUTED], (from ARDUINO_SKETCHBOOK and ALTERNATE_CORE))
+    else
+        $(call show_config_variable,ALTERNATE_CORE_PATH,[USER])
+    endif
+
+    ifndef ARDUINO_VAR_PATH
+        ARDUINO_VAR_PATH  = $(ALTERNATE_CORE_PATH)/variants
+        $(call show_config_variable,ARDUINO_VAR_PATH,[COMPUTED],(from ALTERNATE_CORE_PATH))
+    endif
+
+    ifndef BOARDS_TXT
+        BOARDS_TXT  = $(ALTERNATE_CORE_PATH)/boards.txt
+        $(call show_config_variable,BOARDS_TXT,[COMPUTED],(from ALTERNATE_CORE_PATH))
+    endif
+
+else
+
+    ifndef ARDUINO_VAR_PATH
+        ARDUINO_VAR_PATH  = $(ARDUINO_DIR)/hardware/$(ARDMK_VENDOR)/$(ARCHITECTURE)/variants
+        $(call show_config_variable,ARDUINO_VAR_PATH,[COMPUTED],(from ARDUINO_DIR))
+    else
+        $(call show_config_variable,ARDUINO_VAR_PATH,[USER])
+    endif
+
+    ifndef BOARDS_TXT
+        BOARDS_TXT  = $(ARDUINO_DIR)/hardware/$(ARDMK_VENDOR)/$(ARCHITECTURE)/boards.txt
+        $(call show_config_variable,BOARDS_TXT,[COMPUTED],(from ARDUINO_DIR))
+    else
+        $(call show_config_variable,BOARDS_TXT,[USER])
+    endif
+
+endif
+
+ifeq (,$(wildcard $(BOARDS_TXT)))
+    $(error Currently BOARDS_TXT='$(BOARDS_TXT)', which is not an existing file or an invalid filename.)
+endif
+
 ifndef TOOL_PREFIX
     TOOL_PREFIX = avr
 endif
@@ -557,51 +606,6 @@ else
     $(call show_config_variable,ARDUINO_PLATFORM_LIB_PATH,[USER])
 endif
 
-# Third party hardware and core like ATtiny or ATmega 16
-ifdef ALTERNATE_CORE
-    $(call show_config_variable,ALTERNATE_CORE,[USER])
-
-    ifndef ALTERNATE_CORE_PATH
-        ALTERNATE_CORE_PATH = $(ARDUINO_SKETCHBOOK)/hardware/$(ALTERNATE_CORE)/$(ARCHITECTURE)
-    endif
-endif
-
-ifdef ALTERNATE_CORE_PATH
-
-    ifdef ALTERNATE_CORE
-        $(call show_config_variable,ALTERNATE_CORE_PATH,[COMPUTED], (from ARDUINO_SKETCHBOOK and ALTERNATE_CORE))
-    else
-        $(call show_config_variable,ALTERNATE_CORE_PATH,[USER])
-    endif
-
-    ifndef ARDUINO_VAR_PATH
-        ARDUINO_VAR_PATH  = $(ALTERNATE_CORE_PATH)/variants
-        $(call show_config_variable,ARDUINO_VAR_PATH,[COMPUTED],(from ALTERNATE_CORE_PATH))
-    endif
-
-    ifndef BOARDS_TXT
-        BOARDS_TXT  = $(ALTERNATE_CORE_PATH)/boards.txt
-        $(call show_config_variable,BOARDS_TXT,[COMPUTED],(from ALTERNATE_CORE_PATH))
-    endif
-
-else
-
-    ifndef ARDUINO_VAR_PATH
-        ARDUINO_VAR_PATH  = $(ARDUINO_DIR)/hardware/$(ARDMK_VENDOR)/$(ARCHITECTURE)/variants
-        $(call show_config_variable,ARDUINO_VAR_PATH,[COMPUTED],(from ARDUINO_DIR))
-    else
-        $(call show_config_variable,ARDUINO_VAR_PATH,[USER])
-    endif
-
-    ifndef BOARDS_TXT
-        BOARDS_TXT  = $(ARDUINO_DIR)/hardware/$(ARDMK_VENDOR)/$(ARCHITECTURE)/boards.txt
-        $(call show_config_variable,BOARDS_TXT,[COMPUTED],(from ARDUINO_DIR))
-    else
-        $(call show_config_variable,BOARDS_TXT,[USER])
-    endif
-
-endif
-
 ########################################################################
 # Miscellaneous
 

Common.mk

@@ -7,7 +7,13 @@ dir_if_exists = $(if $(wildcard $(1)$(2)),$(1))
 
 ifndef PARSE_BOARD
 # result = $(call READ_BOARD_TXT, 'boardname', 'parameter')
-PARSE_BOARD = $(shell grep -Ev '^\#' $(BOARDS_TXT) | grep -E "^[ \t]*$(1).$(2)=" | cut -d = -f 2 | cut -d : -f 2)
+PARSE_BOARD = $(shell if [ -f $(BOARDS_TXT) ]; \
+then \
+  grep -Ev '^\#' $(BOARDS_TXT) | \
+  grep -E "^[ \t]*$(1).$(2)=" | \
+  cut -d = -f 2 | \
+  cut -d : -f 2; \
+fi)
 endif
 
 # Run a shell script if it exists. Stops make on error.