Fix style script and add comment to failing blocks (#1045)

[skip appveyor]

tools/check-style.sh

 #!/bin/bash
-# 
+#
 # Script to check include/test code for common pybind11 code style errors.
-# 
+#
 # This script currently checks for
 #
 # 1. use of tabs instead of spaces
@@ -11,72 +11,60 @@
 # 5. Missing space between right parenthesis and brace, e.g. 'for (...){'
 # 6. opening brace on its own line. It should always be on the same line as the
 #    if/while/for/do statment.
-# 
+#
 # Invoke as: tools/check-style.sh
 #
 
-errors=0
+check_style_errors=0
 IFS=$'\n'
-found=
-# The mt=41 sets a red background for matched tabs:
-GREP_COLORS='mt=41' GREP_COLOR='41' grep $'\t' include tests/*.{cpp,py,h} docs/*.rst -rn --color=always |
-        while read f; do
-    if [ -z "$found" ]; then
-        echo -e '\033[31m\033[01mError: found tabs instead of spaces in the following files:\033[0m'
-        found=1
-        errors=1
-    fi
-
-    echo "    $f"
-done
-
-found=
-grep -IUlr $'\r' include tests/*.{cpp,py,h} docs/*.rst --color=always |
-        while read f; do
-    if [ -z "$found" ]; then
-        echo -e '\033[31m\033[01mError: found CRLF characters in the following files:\033[0m'
-        found=1
-        errors=1
-    fi
-
-    echo "    $f"
-done
 
-found=
-# The mt=41 sets a red background for matched trailing spaces
-GREP_COLORS='mt=41' GREP_COLOR='41' grep '[[:blank:]]\+$' include tests/*.{cpp,py,h} docs/*.rst -rn --color=always |
-        while read f; do
-    if [ -z "$found" ]; then
-        echo -e '\033[31m\033[01mError: found trailing spaces in the following files:\033[0m'
-        found=1
-        errors=1
-    fi
+found="$( GREP_COLORS='mt=41' GREP_COLOR='41' grep $'\t' include tests/*.{cpp,py,h} docs/*.rst -rn --color=always )"
+if [ -n "$found" ]; then
+    # The mt=41 sets a red background for matched tabs:
+    echo -e '\033[31;01mError: found tab characters in the following files:\033[0m'
+    check_style_errors=1
+    echo "$found" | sed -e 's/^/    /'
+fi
 
-    echo "    $f"
-done
 
-found=
-grep '\<\(if\|for\|while\|catch\)(\|){' include tests/*.{cpp,py,h} -rn --color=always |
-        while read line; do
-    if [ -z "$found" ]; then
-        echo -e '\033[31m\033[01mError: found the following coding style problems:\033[0m'
-        found=1
-        errors=1
-    fi
+found="$( grep -IUlr $'\r' include tests/*.{cpp,py,h} docs/*.rst --color=always )"
+if [ -n "$found" ]; then
+    echo -e '\033[31;01mError: found CRLF characters in the following files:\033[0m'
+    check_style_errors=1
+    echo "$found" | sed -e 's/^/    /'
+fi
 
-    echo "    $line"
-done
+found="$(GREP_COLORS='mt=41' GREP_COLOR='41' grep '[[:blank:]]\+$' include tests/*.{cpp,py,h} docs/*.rst -rn --color=always )"
+if [ -n "$found" ]; then
+    # The mt=41 sets a red background for matched trailing spaces
+    echo -e '\033[31;01mError: found trailing spaces in the following files:\033[0m'
+    check_style_errors=1
+    echo "$found" | sed -e 's/^/    /'
+fi
 
-found=
-GREP_COLORS='mt=41' GREP_COLOR='41' grep '^\s*{\s*$' include docs/*.rst -rn --color=always |
-        while read f; do
-    if [ -z "$found" ]; then
-        echo -e '\033[31m\033[01mError: braces should occur on the same line as the if/while/.. statement. Found issues in the following files: \033[0m'
-        found=1
-        errors=1
-    fi
+found="$(grep '\<\(if\|for\|while\|catch\)(\|){' include tests/*.{cpp,h} -rn --color=always)"
+if [ -n "$found" ]; then
+    echo -e '\033[31;01mError: found the following coding style problems:\033[0m'
+    check_style_errors=1
+    echo "$found" | sed -e 's/^/    /'
+fi
 
-    echo "    $f"
-done
+found="$(awk '
+function prefix(filename, lineno) {
+    return "    \033[35m" filename "\033[36m:\033[32m" lineno "\033[36m:\033[0m"
+}
+function mark(pattern, string) { sub(pattern, "\033[01;31m&\033[0m", string); return string }
+last && /^\s*{/ {
+    print prefix(FILENAME, FNR-1) mark("\\)\\s*$", last)
+    print prefix(FILENAME, FNR)   mark("^\\s*{", $0)
+    last=""
+}
+{ last = /(if|for|while|catch|switch)\s*\(.*\)\s*$/ ? $0 : "" }
+' $(find include -type f) tests/*.{cpp,h} docs/*.rst)"
+if [ -n "$found" ]; then
+    check_style_errors=1
+    echo -e '\033[31;01mError: braces should occur on the same line as the if/while/.. statement. Found issues in the following files:\033[0m'
+    echo "$found"
+fi
 
-exit $errors
+exit $check_style_errors