Use structopt instead of docopt.

This commit refactors the Wasmtime CLI tools to use `structopt` instead of
`docopt`.

The `wasmtime` tool now has the following subcommands:

* `config new` - creates a new Wasmtime configuration file.
* `run` - runs a WebAssembly module.
* `wasm2obj` - translates a Wasm module to native object file.
* `wast` - runs a test script file.

If no subcommand is specified, the `run` subcommand is used. Thus,
`wasmtime foo.wasm` should continue to function as expected.

The `wasm2obj` and `wast` tools still exist, but delegate to the same
implementation as the `wasmtime` subcommands.  The standalone `wasm2obj` and
`wast` tools may be removed in the future in favor of simply using `wasmtime`.

Included in this commit is a breaking change to the default Wasmtime
configuration file: it has been renamed from `wasmtime-cache-config.toml` to
simply `config.toml`.  The new name is less specific which will allow for
additional (non-cache-related) settings in the future.

There are some breaking changes to improve command line UX:

* The `--cache-config` option has been renamed to `--config`.
* The `--create-config-file` option has moved to the `config new` subcommand.
As a result, the `wasm2obj` and `wast` tools cannot be used to create a new
config file.
* The short form of the `--optimize` option has changed from
`-o` to `-O` for consistency.
* The `wasm2obj` command takes the output object file as a
required positional argument rather than the former required output *option*
(e.g. `wasmtime wasm2obj foo.wasm foo.obj`).

src/commands/wasm2obj.rs

@@ -0,0 +1,205 @@
+//! The module that implements the `wasmtime wasm2obj` command.
+
+use crate::{init_file_per_thread_logger, pick_compilation_strategy, CommonOptions};
+use anyhow::{anyhow, bail, Context as _, Result};
+use faerie::Artifact;
+use std::{
+    fmt::Write,
+    fs::File,
+    path::{Path, PathBuf},
+    str::FromStr,
+};
+use structopt::{clap::AppSettings, StructOpt};
+use target_lexicon::Triple;
+use wasmtime::Strategy;
+use wasmtime_debug::{emit_debugsections, read_debuginfo};
+#[cfg(feature = "lightbeam")]
+use wasmtime_environ::Lightbeam;
+use wasmtime_environ::{
+    cache_init, entity::EntityRef, settings, settings::Configurable, wasm::DefinedMemoryIndex,
+    Compiler, Cranelift, ModuleEnvironment, ModuleVmctxInfo, Tunables, VMOffsets,
+};
+use wasmtime_jit::native;
+use wasmtime_obj::emit_module;
+
+/// The after help text for the `wasm2obj` command.
+pub const WASM2OBJ_AFTER_HELP: &str =
+    "The translation is dependent on the environment chosen.\n\
+     The default is a dummy environment that produces placeholder values.";
+
+fn parse_target(s: &str) -> Result<Triple> {
+    Triple::from_str(&s).map_err(|e| anyhow!(e))
+}
+
+/// Translates a WebAssembly module to native object file
+#[derive(StructOpt)]
+#[structopt(
+    name = "wasm2obj",
+    version = env!("CARGO_PKG_VERSION"),
+    setting = AppSettings::ColoredHelp,
+    after_help = WASM2OBJ_AFTER_HELP,
+)]
+pub struct WasmToObjCommand {
+    #[structopt(flatten)]
+    common: CommonOptions,
+
+    /// The path of the WebAssembly module to translate
+    #[structopt(index = 1, value_name = "MODULE_PATH", parse(from_os_str))]
+    module: PathBuf,
+
+    /// The path of the output object file
+    #[structopt(index = 2, value_name = "OUTPUT_PATH")]
+    output: String,
+
+    /// The target triple; default is the host triple
+    #[structopt(long, value_name = "TARGET", parse(try_from_str = parse_target))]
+    target: Option<Triple>,
+}
+
+impl WasmToObjCommand {
+    /// Executes the command.
+    pub fn execute(&self) -> Result<()> {
+        let log_config = if self.common.debug {
+            pretty_env_logger::init();
+            None
+        } else {
+            let prefix = "wasm2obj.dbg.";
+            init_file_per_thread_logger(prefix);
+            Some(prefix)
+        };
+
+        let errors = cache_init(
+            !self.common.disable_cache,
+            self.common.config.as_ref(),
+            log_config,
+        );
+
+        if !errors.is_empty() {
+            let mut message = String::new();
+            writeln!(message, "Cache initialization failed. Errors:")?;
+            for e in errors {
+                writeln!(message, "  -> {}", e)?;
+            }
+            bail!(message);
+        }
+
+        self.handle_module()
+    }
+
+    fn handle_module(&self) -> Result<()> {
+        let strategy = pick_compilation_strategy(self.common.cranelift, self.common.lightbeam)?;
+
+        let data = wat::parse_file(&self.module).context("failed to parse module")?;
+
+        let isa_builder = match self.target.as_ref() {
+            Some(target) => native::lookup(target.clone())?,
+            None => native::builder(),
+        };
+        let mut flag_builder = settings::builder();
+
+        // There are two possible traps for division, and this way
+        // we get the proper one if code traps.
+        flag_builder.enable("avoid_div_traps").unwrap();
+
+        if self.common.enable_simd {
+            flag_builder.enable("enable_simd").unwrap();
+        }
+
+        if self.common.optimize {
+            flag_builder.set("opt_level", "speed").unwrap();
+        }
+
+        let isa = isa_builder.finish(settings::Flags::new(flag_builder));
+
+        let mut obj = Artifact::new(isa.triple().clone(), self.output.clone());
+
+        // TODO: Expose the tunables as command-line flags.
+        let tunables = Tunables::default();
+
+        let (
+            module,
+            module_translation,
+            lazy_function_body_inputs,
+            lazy_data_initializers,
+            target_config,
+        ) = {
+            let environ = ModuleEnvironment::new(isa.frontend_config(), tunables);
+
+            let translation = environ
+                .translate(&data)
+                .context("failed to translate module")?;
+
+            (
+                translation.module,
+                translation.module_translation.unwrap(),
+                translation.function_body_inputs,
+                translation.data_initializers,
+                translation.target_config,
+            )
+        };
+
+        // TODO: use the traps information
+        let (compilation, relocations, address_transform, value_ranges, stack_slots, _traps) =
+            match strategy {
+                Strategy::Auto | Strategy::Cranelift => Cranelift::compile_module(
+                    &module,
+                    &module_translation,
+                    lazy_function_body_inputs,
+                    &*isa,
+                    self.common.debug_info,
+                ),
+                #[cfg(feature = "lightbeam")]
+                Strategy::Lightbeam => Lightbeam::compile_module(
+                    &module,
+                    &module_translation,
+                    lazy_function_body_inputs,
+                    &*isa,
+                    generate_debug_info,
+                ),
+                #[cfg(not(feature = "lightbeam"))]
+                Strategy::Lightbeam => bail!("lightbeam support not enabled"),
+                other => bail!("unsupported compilation strategy {:?}", other),
+            }
+            .context("failed to compile module")?;
+
+        let module_vmctx_info = {
+            let ofs = VMOffsets::new(target_config.pointer_bytes(), &module);
+            let memory_offset =
+                ofs.vmctx_vmmemory_definition_base(DefinedMemoryIndex::new(0)) as i64;
+            ModuleVmctxInfo {
+                memory_offset,
+                stack_slots,
+            }
+        };
+
+        emit_module(
+            &mut obj,
+            &module,
+            &compilation,
+            &relocations,
+            &lazy_data_initializers,
+            &target_config,
+        )
+        .map_err(|e| anyhow!(e))
+        .context("failed to emit module")?;
+
+        if self.common.debug_info {
+            let debug_data = read_debuginfo(&data);
+            emit_debugsections(
+                &mut obj,
+                &module_vmctx_info,
+                target_config,
+                &debug_data,
+                &address_transform,
+                &value_ranges,
+            )
+            .context("failed to emit debug sections")?;
+        }
+
+        // FIXME: Make the format a parameter.
+        let file = File::create(Path::new(&self.output)).context("failed to create object file")?;
+        obj.write(file).context("failed to write object file")?;
+
+        Ok(())
+    }
+}