Add realpath support to pkg (#7981)

* Add realpath support to pkg

The `pkg` script (along with our build scripts) makes use of `realpath`.
But unlike the build scripts, `pkg` does not have a backup `realpath`
function if the host OS does not have `realpath`.
#7981 adds a backup `realpath` function to the
`pkg` script.

* realpath -e -> realpath

* Improve realpath function and detection

* Use GNU realpath if realpath -e does not work

If realpath -e oes not work, the `realpath` binary is probably BSD
realpath.

* Add grealpath to paths to check for macOS/FreeBSD support

build/functions.sh

@@ -13,16 +13,44 @@
 #
 # shellcheck shell=ash
 
-if ! type -p realpath; then
-	# by default, macOS does not have realpath
-	realpath() {
-		ls "$(
-			cd "$(dirname "$0")"
-			pwd -P # -P resolves symlinks
-		)/$(basename "$0")"
-	}
-	export -f realpath
-fi;
+# macOS's version of realpath does not resolve symlinks, so we add a function
+# for it.
+get_realpath() {
+	local bin
+	local found=''
+	first_realpath="$(type -P realpath)"
+	for bin in $(type -aP grealpath realpath | uniq); do
+		if "$bin" -e . >/dev/null 2>&1; then
+			found=y
+			break
+		fi
+	done
+	if [[ -n "$found" ]]; then
+		if [[ "$first_realpath" == "$bin" ]]; then
+			# Default realpath works.
+			return
+		fi
+		realpath_path="$bin"
+		# by default, macOS does not have realpath
+		eval "$(<<FUNCTION cat
+		realpath() {
+			"$realpath_path" "\$@"
+		}
+FUNCTION
+		)"
+		export -f realpath
+	else
+			cat <<'MESSAGE'
+GNU realpath is required to build Apache Traffic Control if your
+realpath binary does not support the -e flag, as is the case on BSD-like
+operating systems like macOS. Install it by running the following
+command:
+    brew install coreutils
+MESSAGE
+			exit 1
+	fi
+}
+get_realpath
 
 if { ! stat -c%u . >/dev/null && stat -f%u .; } >/dev/null 2>&1; then
 	#BSD stat uses -f as its formatting flag instead of -c

docs/source/development/building.rst

@@ -168,8 +168,8 @@ Install the Dependencies
 	+---------------------------------+---------------------+----------------------------+------------------------+---------------------------+---------------------------+--------------------------+----------+------------------------------+--------------------------+
 	| OS/Package Manager              | Common dependencies | :ref:`dev-traffic-monitor` | :ref:`dev-traffic-ops` | :ref:`dev-traffic-portal` | :ref:`dev-traffic-router` | :ref:`dev-traffic-stats` | Grove    | Grove TC Config (grovetccfg) | :ref:`Docs <docs-guide>` |
 	+=================================+=====================+============================+========================+===========================+===========================+==========================+==========+==============================+==========================+
-	| macOS\ [#mac-jdk]_              | - rpm               | - go                       | - go                   | - npm                     | - maven                   | - go                     | - go     | - go                         | - python3                |
-	| (homebrew_)                     |                     |                            |                        | - grunt-cli               |                           |                          |          |                              |                          |
+	| macOS\ [#mac-jdk]_              | - coreutils         | - go                       | - go                   | - npm                     | - maven                   | - go                     | - go     | - go                         | - python3                |
+	| (homebrew_)                     | - rpm               |                            |                        | - grunt-cli               |                           |                          |          |                              |                          |
 	+---------------------------------+---------------------+----------------------------+------------------------+---------------------------+---------------------------+--------------------------+----------+------------------------------+--------------------------+
 	| Rocky\ Linux\ [#rocky-go]_,     | - git               |                            |                        | - epel-release            | - java-11-openjdk         |                          |          |                              | - python3-devel          |
 	| Red Hat,                        | - rpm-build         |                            |                        | - npm                     | - maven                   |                          |          |                              | - gcc                    |

pkg

@@ -12,6 +12,45 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# macOS's version of realpath does not resolve symlinks, so we add a function
+# for it.
+get_realpath() {
+	local bin
+	local found=''
+	first_realpath="$(type -P realpath)"
+	for bin in $(type -aP grealpath realpath | uniq); do
+		if "$bin" -e . >/dev/null 2>&1; then
+			found=y
+			break
+		fi
+	done
+	if [[ -n "$found" ]]; then
+		if [[ "$first_realpath" == "$bin" ]]; then
+			# Default realpath works.
+			return
+		fi
+		realpath_path="$bin"
+		# by default, macOS does not have realpath
+		eval "$(<<FUNCTION cat
+		realpath() {
+			"$realpath_path" "\$@"
+		}
+FUNCTION
+		)"
+		export -f realpath
+	else
+			cat <<'MESSAGE'
+GNU realpath is required to build Apache Traffic Control if your
+realpath binary does not support the -e flag, as is the case on BSD-like
+operating systems like macOS. Install it by running the following
+command:
+    brew install coreutils
+MESSAGE
+			exit 1
+	fi
+}
+get_realpath
+
 # Files are relative to this script directory.
 SELF="${BASH_SOURCE[0]}"
 cd "$( dirname "${BASH_SOURCE[0]}" )"