Merge #12757: Clarify include guard naming convention

3bcc0059b8 Add lint-include-guards.sh which checks include guard consistency (practicalswift)
8fd6af89a0 Fix missing or inconsistent include guards (practicalswift)
8af65d96f4 Document include guard convention (practicalswift)

Pull request description:

  * **Documentation**: Document include guard convention
  * **Fix**: Fix missing or inconsistent include guards
  * **Regression test**: Add `lint-include-guards.sh` which checks include guard consistency

Tree-SHA512: 8171878f60fd08ccbea943a11e835195750592abb9d7ab74eaa4265ae7fac523b1da9d31ca13d6ab73dd596e49986bfb7593c696e5f39567c93e610165bc2acc

contrib/devtools/lint-include-guards.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+#
+# Copyright (c) 2018 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#
+# Check include guards.
+
+HEADER_ID_PREFIX="BITCOIN_"
+HEADER_ID_SUFFIX="_H"
+
+REGEXP_EXCLUDE_FILES_WITH_PREFIX="src/(crypto/ctaes/|leveldb/|secp256k1/|tinyformat.h|univalue/)"
+
+EXIT_CODE=0
+for HEADER_FILE in $(git ls-files -- "*.h" | grep -vE "^${REGEXP_EXCLUDE_FILES_WITH_PREFIX}")
+do
+    HEADER_ID_BASE=$(cut -f2- -d/ <<< "${HEADER_FILE}" | sed "s/\.h$//g" | tr / _ | tr "[:lower:]" "[:upper:]")
+    HEADER_ID="${HEADER_ID_PREFIX}${HEADER_ID_BASE}${HEADER_ID_SUFFIX}"
+    if [[ $(grep -cE "^#(ifndef|define) ${HEADER_ID}" "${HEADER_FILE}") != 2 ]]; then
+        echo "${HEADER_FILE} seems to be missing the expected include guard:"
+        echo "  #ifndef ${HEADER_ID}"
+        echo "  #define ${HEADER_ID}"
+        echo "  ..."
+        echo "  #endif // ${HEADER_ID}"
+        echo
+        EXIT_CODE=1
+    fi
+done
+exit ${EXIT_CODE}