add shortenPerlShebang function

This setup hook modifies a Perl script so that any "-I" flags in its shebang
line are rewritten into a "use lib ..." statement on the next line. This gets
around a limitation in Darwin, which will not properly handle a script whose
shebang line exceeds 511 characters.

1 files changed, 88 insertions, 0 deletions

diff --git a/pkgs/build-support/setup-hooks/shorten-perl-shebang.sh b/pkgs/build-support/setup-hooks/shorten-perl-shebang.sh
new file mode 100644
index 00000000000..4bf7c0ff1af
--- /dev/null
+++ b/pkgs/build-support/setup-hooks/shorten-perl-shebang.sh
@@ -0,0 +1,88 @@
+# This setup hook modifies a Perl script so that any "-I" flags in its shebang
+# line are rewritten into a "use lib ..." statement on the next line. This gets
+# around a limitation in Darwin, which will not properly handle a script whose
+# shebang line exceeds 511 characters.
+#
+# Each occurrence of "-I /path/to/lib1" or "-I/path/to/lib2" is removed from
+# the shebang line, along with the single space that preceded it. These library
+# paths are placed into a new line of the form
+#
+#     use lib "/path/to/lib1", "/path/to/lib2";
+#
+# immediately following the shebang line. If a library appeared in the original
+# list more than once, only its first occurrence will appear in the output
+# list. In other words, the libraries are deduplicated, but the ordering of the
+# first appearance of each one is preserved.
+#
+# Any flags other than "-I" in the shebang line are left as-is, and the
+# interpreter is also left alone (although the script will abort if the
+# interpreter does not seem to be either "perl" or else "env" with "perl" as
+# its argument). Each line after the shebang line is left unchanged. Each file
+# is modified in place.
+#
+# Usage:
+#     shortenPerlShebang SCRIPT...
+
+shortenPerlShebang() {
+    while [ $# -gt 0 ]; do
+        _shortenPerlShebang "$1"
+        shift
+    done
+}
+
+_shortenPerlShebang() {
+    local program="$1"
+
+    echo "shortenPerlShebang: rewriting shebang line in $program"
+
+    if ! isScript "$program"; then
+        die "shortenPerlShebang: refusing to modify $program because it is not a script"
+    fi
+
+    local temp="$(mktemp)"
+
+    gawk '
+        (NR == 1) {
+            if (!($0 ~ /\/(perl|env +perl)\>/)) {
+                print "shortenPerlShebang: script does not seem to be a Perl script" > "/dev/stderr"
+                exit 1
+            }
+            idx = 0
+            while (match($0, / -I ?([^ ]+)/, pieces)) {
+                matches[idx] = pieces[1]
+                idx++
+                $0 = gensub(/ -I ?[^ ]+/, "", 1, $0)
+            }
+            print $0
+            if (idx > 0) {
+                prefix = "use lib "
+                for (idx in matches) {
+                    path = matches[idx]
+                    if (!(path in seen)) {
+                        printf "%s\"%s\"", prefix, path
+                        seen[path] = 1
+                        prefix = ", "
+                    }
+                }
+                print ";"
+            }
+        }
+        (NR > 1 ) {
+            print
+        }
+    ' "$program" > "$temp" || die
+	# Preserve the mode of the original file
+	cp --preserve=mode --attributes-only "$program" "$temp"
+	mv "$temp" "$program"
+
+    # Measure the new shebang line length and make sure it's okay. We subtract
+    # one to account for the trailing newline that "head" included in its
+    # output.
+    local new_length=$(( $(head -n 1 "$program" | wc -c) - 1 ))
+
+    # Darwin is okay when the shebang line contains 511 characters, but not
+    # when it contains 512 characters.
+    if [ $new_length -ge 512 ]; then
+        die "shortenPerlShebang: shebang line is $new_length characters--still too long for Darwin!"
+    fi
+}