[6/9] check-package: check *.mk files

diff --git a/support/scripts/checkpackagelib_mk.py b/support/scripts/checkpackagelib_mk.py
index 1ff0973dd..40574584a 100644
--- a/support/scripts/checkpackagelib_mk.py
+++ b/support/scripts/checkpackagelib_mk.py
@@ -4,8 +4,182 @@ 
 # menu options using "make menuconfig" and by running "make" with appropriate
 # packages enabled.
 
+import re
+
 # Notice: ignore 'imported but unused' from pyflakes for check functions.
 from checkpackagelib import check_consecutive_empty_lines
 from checkpackagelib import check_empty_last_line
 from checkpackagelib import check_newline_at_eof
 from checkpackagelib import check_trailing_space
+
+# used by more than one function
+ENDS_WITH_BACKSLASH = re.compile(r"^[^#].*\\$")
+
+COMMENT = re.compile("^\s*#")
+CONDITIONAL = re.compile("^\s*(ifeq|ifneq|endif)\s")
+END_DEFINE = re.compile("^\s*endef\s")
+MAKEFILE_TARGET = re.compile("^[^# \t]+:\s")
+START_DEFINE = re.compile("^\s*define\s")
+
+
+def check_indent(
+        fname, args, lineno=0, text=None, start=False, end=False):
+    if start:
+        check_indent.define = False
+        check_indent.backslash = False
+        check_indent.makefile_target = False
+        return
+    if end:
+        return
+
+    if START_DEFINE.search(text):
+        check_indent.define = True
+        return
+    if END_DEFINE.search(text):
+        check_indent.define = False
+        return
+
+    expect_tabs = False
+    if (check_indent.define or check_indent.backslash or
+            check_indent.makefile_target):
+        expect_tabs = True
+    if CONDITIONAL.search(text):
+        expect_tabs = False
+
+    # calculate for next line
+    if ENDS_WITH_BACKSLASH.search(text):
+        check_indent.backslash = True
+    else:
+        check_indent.backslash = False
+
+    if MAKEFILE_TARGET.search(text):
+        check_indent.makefile_target = True
+        return
+    if text.strip() == "":
+        check_indent.makefile_target = False
+        return
+
+    # comment can be indented or not inside define ... endef, so ignore it
+    if check_indent.define and COMMENT.search(text):
+        return
+
+    if expect_tabs:
+        if not text.startswith("\t"):
+            return ["{}:{}: expected indent with tabs"
+                    .format(fname, lineno),
+                    text]
+    else:
+        if text.startswith("\t"):
+            return ["{}:{}: unexpected indent with tabs"
+                    .format(fname, lineno),
+                    text]
+
+
+def check_package_header(
+        fname, args, lineno=0, text=None, start=False, end=False):
+    if start:
+        check_package_header.skip = False
+        return
+    if end or check_package_header.skip or lineno > 6:
+        return
+
+    if lineno in [1, 5]:
+        if lineno == 1 and text.startswith("include "):
+            check_package_header.skip = True
+            return
+        if text.rstrip() != "#" * 80:
+            return ["{}:{}: should be 80 hashes ({}#writing-rules-mk)"
+                    .format(fname, lineno, args.manual_url),
+                    text,
+                    "#" * 80]
+    elif lineno in [2, 4]:
+        if text.rstrip() != "#":
+            return ["{}:{}: should be 1 hash ({}#writing-rules-mk)"
+                    .format(fname, lineno, args.manual_url),
+                    text]
+    elif lineno == 6:
+        if text.rstrip() != "":
+            return ["{}:{}: should be a blank line ({}#writing-rules-mk)"
+                    .format(fname, lineno, args.manual_url),
+                    text]
+
+
+TAB_OR_MULTIPLE_SPACES_BEFORE_BACKSLASH = re.compile(r"^.*(  |\t)\\$")
+
+
+def check_space_before_backslash(
+        fname, args, lineno=0, text=None, start=False, end=False):
+    if start or end:
+        return
+
+    if TAB_OR_MULTIPLE_SPACES_BEFORE_BACKSLASH.match(text.rstrip()):
+        return ["{}:{}: use only one space before backslash"
+                .format(fname, lineno),
+                text]
+
+
+def check_trailing_backslash(
+        fname, args, lineno=0, text=None, start=False, end=False):
+    if start:
+        check_trailing_backslash.backslash = False
+        return
+    if end:
+        return
+
+    last_line_ends_in_backslash = check_trailing_backslash.backslash
+
+    # calculate for next line
+    if ENDS_WITH_BACKSLASH.search(text):
+        check_trailing_backslash.backslash = True
+        check_trailing_backslash.lastline = text
+        return
+    check_trailing_backslash.backslash = False
+
+    if last_line_ends_in_backslash and text.strip() == "":
+        return ["{}:{}: remove trailing backslash"
+                .format(fname, lineno - 1),
+                check_trailing_backslash.lastline]
+
+
+DEFAULT_AUTOTOOLS_FLAG = re.compile("^.*{}".format("|".join([
+    "_AUTORECONF\s*=\s*NO",
+    "_LIBTOOL_PATCH\s*=\s*YES"])))
+DEFAULT_GENERIC_FLAG = re.compile("^.*{}".format("|".join([
+    "_INSTALL_IMAGES\s*=\s*NO",
+    "_INSTALL_REDISTRIBUTE\s*=\s*YES",
+    "_INSTALL_STAGING\s*=\s*NO",
+    "_INSTALL_TARGET\s*=\s*YES"])))
+END_CONDITIONAL = re.compile("^\s*(endif)")
+START_CONDITIONAL = re.compile("^\s*(ifeq|ifneq)")
+
+
+def check_useless_flag(
+        fname, args, lineno=0, text=None, start=False, end=False):
+    if start:
+        check_useless_flag.conditional = 0
+        return
+    if end:
+        return
+
+    if START_CONDITIONAL.search(text):
+        check_useless_flag.conditional += 1
+        return
+    if END_CONDITIONAL.search(text):
+        check_useless_flag.conditional -= 1
+        return
+
+    # allow non-default conditionally overridden by default
+    if check_useless_flag.conditional > 0:
+        return
+
+    if DEFAULT_GENERIC_FLAG.search(text):
+        return ["{}:{}: useless default value "
+                "({}#_infrastructure_for_packages_with_specific_build_systems)"
+                .format(fname, lineno, args.manual_url),
+                text]
+
+    if DEFAULT_AUTOTOOLS_FLAG.search(text):
+        return ["{}:{}: useless default value "
+                "({}#_infrastructure_for_autotools_based_packages)"
+                .format(fname, lineno, args.manual_url),
+                text]