lang: Add fuzz target to lang Makefile

lang/fuzz/.gitignore

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+corpus/
+crashers/
+suppressions/
+fuzz-fuzz.zip

lang/fuzz/Makefile

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+# Mgmt
+# Copyright (C) 2013-2020+ James Shubin and the project contributors
+# Written by James Shubin <james@shubin.ca> and the project contributors
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+SHELL = /usr/bin/env bash
+.PHONY: all fuzz
+
+all: fuzz
+
+fuzz:
+	mkdir -p corpus
+	find ../.. -name \*.mcl -exec cp {} corpus \;
+	go-fuzz-build
+	go-fuzz -bin=./lang-fuzz.zip -workdir=.

lang/fuzz/fuzz.go

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+// Mgmt
+// Copyright (C) 2013-2020+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package fuzz
+
+import (
+	"bytes"
+
+	"github.com/purpleidea/mgmt/lang"
+)
+
+// Fuzz is repeatedly called by go-fuzz with semi-random inputs in an attempt to
+// make the Lexer/Parser crash. From the go-fuzz docs: Data is a random input
+// generated by go-fuzz, note that in most cases it is invalid. The function
+// must return 1 if the fuzzer should increase priority of the given input
+// during subsequent fuzzing (for example, the input is lexically correct and
+// was parsed successfully); -1 if the input must not be added to corpus even if
+// gives new coverage; and 0 otherwise; other values are reserved for future
+// use.
+func Fuzz(data []byte) int {
+	ast, err := lang.LexParse(bytes.NewReader(data))
+	if err != nil {
+		if ast != nil {
+			panic("ast != nil on error")
+		}
+		return 0
+	}
+	return 1
+}