Address review remarks

docker/download.sh

@@ -1,5 +1,22 @@
 #!/bin/bash
 
+if [[ $# -ne 2 ]] ; then 
+    echo "The $0 utility requires two input arguments:"
+    echo "- Arch for compilers to download. See https://github.com/ethereum/solc-bin for available archs."
+    echo "- Target directory to store the downloaded compilers."
+    echo ""
+    echo "Note that to use custom compiler cache path, the env variable SOL_AST_COMPILER_CACHE should be set."
+    echo "See README.md for the details."
+    echo ""
+    echo "Example:"
+    echo ""
+    echo "$0 'wasm' path/to/compiler/cache"
+    echo "export SOL_AST_COMPILER_CACHE=path/to/compiler/cache"
+    echo "sol-ast-compile --locate-compiler-cache"
+
+    exit 1;
+fi
+
 ARCH="${1}"
 CACHE_DIR="${2}"
 TARGET_DIR="$CACHE_DIR/$ARCH"

src/compile/kinds/compiler.ts

@@ -142,12 +142,12 @@ export async function getCompilerForVersion<T extends CompilerMapping>(
         );
 
         /**
-         * Native compilers are exeсutable files, so give them valid permissions.
-         * WASM compilers are loaded by NodeJS, so write them as common files.
+         * Native compilers are exeсutable files, so give them proper permissions.
+         * WASM compilers are loaded by NodeJS, so write them as readonly common files.
          */
-        const options = kind === CompilerKind.Native ? { mode: 0o555 } : undefined;
+        const permissions = kind === CompilerKind.Native ? 0o555 : 0o444;
 
-        await fse.writeFile(compilerLocalPath, response.data, options);
+        await fse.writeFile(compilerLocalPath, response.data, { mode: permissions });
     }
 
     if (kind === CompilerKind.Native) {