[decompiler] Downgrade to bytecode v6 for Revela (aptos-labs#15597)

Since the bytecode version default is v7, Revela cannot be used at all anymore. This PR attempts to downgrade to v6 before calling Revela, if possible. This allows to continue to work with Revela until the new decompiler is available.

Author: wrwg

crates/aptos/CHANGELOG.md

@@ -3,6 +3,7 @@
 All notable changes to the Aptos CLI will be captured in this file. This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html) and the format set out by [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 # Unreleased
+- Downgrade bytecode version to v6 before calling the Revela decompiler, if possible, i.e. no enum types are used. This allows to continue to use Revela until the new decompiler is ready.
 
 ## [5.0.0] - 2024/12/11
 - [**Breaking Change**] `aptos init` and `aptos account fund-with-faucet` no longer work directly with testnet, you must now use the minting page at the [Aptos dev docs](https://aptos.dev/network/faucet). 

crates/aptos/src/move_tool/bytecode.rs

@@ -20,7 +20,8 @@ use async_trait::async_trait;
 use clap::{Args, Parser};
 use itertools::Itertools;
 use move_binary_format::{
-    binary_views::BinaryIndexedView, file_format::CompiledScript, CompiledModule,
+    binary_views::BinaryIndexedView, file_format::CompiledScript, file_format_common,
+    CompiledModule,
 };
 use move_bytecode_source_map::{mapping::SourceMapping, utils::source_map_from_file};
 use move_command_line_common::files::{
@@ -37,6 +38,7 @@ use std::{
     process::Command,
     str,
 };
+use tempfile::NamedTempFile;
 
 const DISASSEMBLER_EXTENSION: &str = "mv.asm";
 const DECOMPILER_EXTENSION: &str = "mv.move";
@@ -323,7 +325,14 @@ impl BytecodeCommand {
         let exe = get_revela_path()?;
         let to_cli_error = |e| CliError::IO(exe.display().to_string(), e);
         let mut cmd = Command::new(exe.as_path());
-        cmd.arg(format!("--bytecode={}", bytecode_path.display()));
+        // WORKAROUND: if the bytecode is v7, try to downgrade to v6 since Revela
+        // does not support v7
+        let v6_temp_file = self.downgrade_to_v6(bytecode_path)?;
+        if let Some(file) = &v6_temp_file {
+            cmd.arg(format!("--bytecode={}", file.path().display()));
+        } else {
+            cmd.arg(format!("--bytecode={}", bytecode_path.display()));
+        }
         if self.is_script {
             cmd.arg("--script");
         }
@@ -343,4 +352,49 @@ impl BytecodeCommand {
             )))
         }
     }
+
+    fn downgrade_to_v6(&self, file_path: &Path) -> Result<Option<NamedTempFile>, CliError> {
+        let error_explanation = || {
+            format!(
+                "{} in `{}` contains Move 2 features (e.g. enum types) \
+                types which are not yet supported by the decompiler",
+                if self.is_script { "script " } else { "module" },
+                file_path.display()
+            )
+        };
+        let create_new_bytecode = |bytes: &[u8]| -> Result<NamedTempFile, CliError> {
+            let temp_file = NamedTempFile::new()
+                .map_err(|e| CliError::IO("creating v6 temp file".to_string(), e))?;
+            fs::write(temp_file.path(), bytes)
+                .map_err(|e| CliError::IO("writing v6 temp file".to_string(), e))?;
+            Ok(temp_file)
+        };
+        let bytes = read_from_file(file_path)?;
+        if self.is_script {
+            let script = CompiledScript::deserialize(&bytes).map_err(|e| {
+                CliError::UnableToParse("script", format!("cannot deserialize: {}", e))
+            })?;
+            if script.version < file_format_common::VERSION_7 {
+                return Ok(None);
+            }
+            let mut new_bytes = vec![];
+            script
+                .serialize_for_version(Some(file_format_common::VERSION_6), &mut new_bytes)
+                // The only reason why this can fail is because of Move 2 features
+                .map_err(|_| CliError::UnexpectedError(error_explanation()))?;
+            Ok(Some(create_new_bytecode(&new_bytes)?))
+        } else {
+            let module = CompiledModule::deserialize(&bytes).map_err(|e| {
+                CliError::UnableToParse("script", format!("cannot deserialize: {}", e))
+            })?;
+            if module.version < file_format_common::VERSION_7 {
+                return Ok(None);
+            }
+            let mut new_bytes = vec![];
+            module
+                .serialize_for_version(Some(file_format_common::VERSION_6), &mut new_bytes)
+                .map_err(|_| CliError::UnexpectedError(error_explanation()))?;
+            Ok(Some(create_new_bytecode(&new_bytes)?))
+        }
+    }
 }