Patract's modification with Debug feature

* feat(build/debug): Add debug flag for embedding debuginfo

* retain Custom/Name Section in wasm for debug mode

* when in debug, wasm-opt default use `OptimizationPasses::Zero`

* feat(doc/installation): add installation guide to README

src/cmd/build.rs

@@ -88,6 +88,9 @@ pub struct BuildCommand {
     ///   The CLI argument always takes precedence over the profile value.
     #[structopt(long = "optimization-passes")]
     optimization_passes: Option<OptimizationPasses>,
+    /// Enable debug info in the wasm bundle, will contain the Custom Section and Name Section.
+    #[structopt(short = "d", long = "debug")]
+    debug: bool,
 }
 
 impl BuildCommand {
@@ -106,7 +109,13 @@ impl BuildCommand {
                 match manifest.get_profile_optimization_passes() {
                     // if no setting is found, neither on the cli nor in the profile,
                     // then we use the default
-                    None => OptimizationPasses::default(),
+                    None => {
+                        if self.debug {
+                            OptimizationPasses::Zero
+                        } else {
+                            OptimizationPasses::default()
+                        }
+                    },
                     Some(opt_passes) => opt_passes,
                 }
             }
@@ -118,6 +127,7 @@ impl BuildCommand {
             self.build_artifact,
             unstable_flags,
             optimization_passes,
+            self.debug,
         )
     }
 }
@@ -146,6 +156,7 @@ impl CheckCommand {
             BuildArtifacts::CheckOnly,
             unstable_flags,
             OptimizationPasses::Zero,
+            false,
         )
     }
 }
@@ -171,15 +182,23 @@ fn exec_cargo_for_wasm_target(
     command: &str,
     verbosity: Verbosity,
     unstable_flags: &UnstableFlags,
+    debug: bool,
 ) -> Result<()> {
     util::assert_channel()?;
 
     // set linker args via RUSTFLAGS.
     // Currently will override user defined RUSTFLAGS from .cargo/config. See https://github.com/paritytech/cargo-contract/issues/98.
+    if debug {
+        std::env::set_var(
+            "RUSTFLAGS",
+            "-C link-arg=-z -C link-arg=stack-size=65536 -C link-arg=--import-memory -C opt-level=1 -C debuginfo=2",
+        );
+    } else {
     std::env::set_var(
         "RUSTFLAGS",
         "-C link-arg=-z -C link-arg=stack-size=65536 -C link-arg=--import-memory",
     );
+    }
 
     let cargo_build = |manifest_path: &ManifestPath| {
         let target_dir = &crate_metadata.target_directory;
@@ -269,8 +288,14 @@ fn strip_custom_sections(module: &mut Module) {
     });
 }
 
+fn strip_reloc_section(module: &mut Module) {
+    module
+        .sections_mut()
+        .retain(|section| !matches!(section, Section::Reloc(_)));
+}
+
 /// Performs required post-processing steps on the wasm artifact.
-fn post_process_wasm(crate_metadata: &CrateMetadata) -> Result<()> {
+fn post_process_wasm(crate_metadata: &CrateMetadata, debug: bool) -> Result<()> {
     // Deserialize wasm module from a file.
     let mut module =
         parity_wasm::deserialize_file(&crate_metadata.original_wasm).context(format!(
@@ -286,7 +311,11 @@ fn post_process_wasm(crate_metadata: &CrateMetadata) -> Result<()> {
         anyhow::bail!("Optimizer failed");
     }
     ensure_maximum_memory_pages(&mut module, MAX_MEMORY_PAGES)?;
+    if debug {
+        strip_reloc_section(&mut module);
+    } else {
     strip_custom_sections(&mut module);
+    }
 
     validate_wasm::validate_import_section(&module)?;
 
@@ -306,6 +335,7 @@ fn post_process_wasm(crate_metadata: &CrateMetadata) -> Result<()> {
 fn optimize_wasm(
     crate_metadata: &CrateMetadata,
     optimization_passes: OptimizationPasses,
+    debug: bool,
 ) -> Result<OptimizationResult> {
     let mut dest_optimized = crate_metadata.dest_wasm.clone();
     dest_optimized.set_file_name(format!(
@@ -316,6 +346,7 @@ fn optimize_wasm(
         crate_metadata.dest_wasm.as_os_str(),
         &dest_optimized.as_os_str(),
         optimization_passes,
+        debug,
     )?;
 
     if !dest_optimized.exists() {
@@ -348,6 +379,7 @@ fn do_optimization(
     dest_wasm: &OsStr,
     dest_optimized: &OsStr,
     optimization_level: OptimizationPasses,
+    debug: bool,
 ) -> Result<()> {
     // check `wasm-opt` is installed
     let which = which::which("wasm-opt");
@@ -388,6 +420,7 @@ fn do_optimization(
         // the memory is initialized to zeroes, otherwise it won't run the
         // memory-packing pre-pass.
         .arg("--zero-filled-memory")
+        .args(if debug { &["--debuginfo"][..] } else { &[][..] })
         .output()
         .map_err(|err| {
             anyhow::anyhow!(
@@ -529,6 +562,7 @@ pub(crate) fn execute(
     build_artifact: BuildArtifacts,
     unstable_flags: UnstableFlags,
     optimization_passes: OptimizationPasses,
+    debug: bool,
 ) -> Result<BuildResult> {
     let crate_metadata = CrateMetadata::collect(&manifest_path)?;
 
@@ -541,30 +575,30 @@ pub(crate) fn execute(
             format!("[1/{}]", build_artifact.steps()).bold(),
             "Building cargo project".bright_green().bold()
         );
-        exec_cargo_for_wasm_target(&crate_metadata, "build", verbosity, &unstable_flags)?;
+        exec_cargo_for_wasm_target(&crate_metadata, "build", verbosity, &unstable_flags, debug)?;
 
         maybe_println!(
             verbosity,
             " {} {}",
             format!("[2/{}]", build_artifact.steps()).bold(),
             "Post processing wasm file".bright_green().bold()
         );
-        post_process_wasm(&crate_metadata)?;
+        post_process_wasm(&crate_metadata, debug)?;
 
         maybe_println!(
             verbosity,
             " {} {}",
             format!("[3/{}]", build_artifact.steps()).bold(),
             "Optimizing wasm file".bright_green().bold()
         );
-        let optimization_result = optimize_wasm(&crate_metadata, optimization_passes)?;
+        let optimization_result = optimize_wasm(&crate_metadata, optimization_passes, debug)?;
 
         Ok(optimization_result)
     };
 
     let (opt_result, metadata_result) = match build_artifact {
         BuildArtifacts::CheckOnly => {
-            exec_cargo_for_wasm_target(&crate_metadata, "check", verbosity, &unstable_flags)?;
+            exec_cargo_for_wasm_target(&crate_metadata, "check", verbosity, &unstable_flags, debug)?;
             (None, None)
         }
         BuildArtifacts::CodeOnly => {