fuzz: add zkas_compile.rs libfuzzer fuzz harness

This should have been done in an earlier commit
(a0e78b576abfb3d408777c44d7bd77cdedf242d5)
but I forgot to add the file.

fuzz/fuzz_targets/zkas_compile.rs

@@ -0,0 +1,84 @@
+/* This file is part of DarkFi (https://dark.fi)
+ *
+ * Copyright (C) 2020-2023 Dyne.org foundation
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+// See also honggfuzz/zkas_compile.rs
+
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use darkfi::zkas::{Lexer, Parser, Compiler, Analyzer};
+use std::str;
+
+fuzz_target!(|data: &[u8]| {
+    // The lex, parse, compile code below is taken from bin/zkas/src/main.rs
+
+    // Use only inputs that can be encoded as .chars(), as this is what the
+    // zkas binary uses
+    let chars = match str::from_utf8(data) {
+        Ok(v) => v.chars(),
+        Err(_e) => return,
+    };
+
+    let filename = "/dev/null";
+    let lexer = Lexer::new(filename, chars.clone());
+    let tokens = match lexer.lex() {
+        Ok(v) => v,
+        Err(_) => return,
+    };
+
+    // The parser goes over the tokens provided by the lexer and builds
+    // the initial AST, not caring much about the semantics, just enforcing
+    // syntax and general structure.
+    let parser = Parser::new(filename, chars.clone(), tokens);
+    let (namespace, k, constants, witnesses, statements) = match parser.parse() {
+        Ok(v) => v,
+        Err(_) => return,
+    };
+
+    // The analyzer goes through the initial AST provided by the parser and
+    // converts return and variable types to their correct forms, and also
+    // checks that the semantics of the ZK script are correct.
+    let mut analyzer = Analyzer::new(filename, chars.clone(), constants, witnesses, statements);
+    if analyzer.analyze_types().is_err() {
+        return
+    }
+
+
+    // Skip this section because it automatically pauses on output which is probably
+    // preventing coverage
+    // if analyzer.analyze_semantic().is_err() {
+    //     return
+    // }
+
+    let compiler = Compiler::new(
+        filename,
+        chars.clone(),
+        namespace,
+        k,
+        analyzer.constants,
+        analyzer.witnesses,
+        analyzer.statements,
+        analyzer.literals,
+        false, // no debug info
+    );
+
+    match compiler.compile() {
+        Ok(v) => v,
+        Err(_) => return,
+    };
+
+});