[Bazel] Support for feature debug fission in emsdk-bazel-toolchain emscripten-core#1479

Author: trzeciak

bazel/BUILD

@@ -78,6 +78,18 @@ alias(
     }),
 )
 
+alias(
+    name = "dwp_files",
+    actual = select({
+        ":linux": "@emscripten_bin_linux//:dwp_files",
+        ":linux_arm64": "@emscripten_bin_linux_arm64//:dwp_files",
+        ":macos": "@emscripten_bin_mac//:dwp_files",
+        ":macos_arm64": "@emscripten_bin_mac_arm64//:dwp_files",
+        ":windows": "@emscripten_bin_win//:dwp_files",
+        "//conditions:default": ":empty",
+    }),
+)
+
 platform(
     name = "platform_wasm",
     constraint_values = [

bazel/emscripten_deps.bzl

@@ -96,6 +96,13 @@ filegroup(
         ],
     ),
 )
+
+filegroup(
+    name = "dwp_files",
+    srcs = [
+        "bin/llvm-dwp{bin_extension}",
+    ],
+)
 """
 
 def emscripten_deps(emscripten_version = "latest"):

bazel/emscripten_toolchain/BUILD.bazel

@@ -43,12 +43,25 @@ filegroup(
     ],
 )
 
+filegroup(
+    name = "dwp_files",
+    srcs = [
+        "emdwp-emscripten_bin_linux_arm64.sh",
+        "emdwp-emscripten_bin_linux.sh",
+        "emdwp-emscripten_bin_mac_arm64.sh",
+        "emdwp-emscripten_bin_mac.sh",
+        "emdwp-emscripten_bin_win.bat",
+        "@emsdk//:dwp_files",
+    ],
+)
+
 filegroup(
     name = "all_files",
     srcs = [
         ":ar_files",
         ":compiler_files",
         ":linker_files",
+        ":dwp_files",
     ],
 )
 
@@ -75,7 +88,7 @@ cc_toolchain(
     ar_files = ":ar_files",
     as_files = ":empty",
     compiler_files = ":compiler_files",
-    dwp_files = ":empty",
+    dwp_files = ":dwp_files",
     linker_files = ":linker_files",
     objcopy_files = ":empty",
     strip_files = ":empty",

bazel/emscripten_toolchain/emdwp-emscripten_bin_linux.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+exec external/emscripten_bin_linux/bin/llvm-dwp "$@"

bazel/emscripten_toolchain/emdwp-emscripten_bin_linux_arm64.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+exec external/emscripten_bin_linux_arm64/bin/llvm-dwp "$@"

bazel/emscripten_toolchain/emdwp-emscripten_bin_mac.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+exec external/emscripten_bin_mac/bin/llvm-dwp "$@"

bazel/emscripten_toolchain/emdwp-emscripten_bin_mac_arm64.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+exec external/emscripten_bin_mac_arm64/bin/llvm-dwp "$@"

bazel/emscripten_toolchain/emdwp-emscripten_bin_win.bat

@@ -0,0 +1,3 @@
+@ECHO OFF
+
+call external\emscripten_bin_win\bin\llvm-dwp %*

bazel/emscripten_toolchain/toolchain.bzl

@@ -72,12 +72,14 @@ def _impl(ctx):
 
     emscripten_dir = ctx.attr.emscripten_binaries.label.workspace_root
     nodejs_path = ctx.file.nodejs_bin.path
+    emscripten_name = ctx.attr.emscripten_binaries.label.repo_name
 
     builtin_sysroot = emscripten_dir + "/emscripten/cache/sysroot"
 
     emcc_script = "emcc.%s" % ctx.attr.script_extension
     emcc_link_script = "emcc_link.%s" % ctx.attr.script_extension
     emar_script = "emar.%s" % ctx.attr.script_extension
+    emdwp_script = "emdwp-%s.%s" % (emscripten_name, ctx.attr.script_extension)
 
     ################################################################
     # Tools
@@ -87,6 +89,7 @@ def _impl(ctx):
     link_tool = tool(path = emcc_link_script)
     archive_tool = tool(path = emar_script)
     strip_tool = tool(path = "NOT_USED_STRIP_TOOL")
+    dwarf_tool = tool(path = emdwp_script) # TODO @unused
 
     #### Legacy tool paths (much of this is redundant with action_configs, but
     #### these are still used for some things)
@@ -99,6 +102,7 @@ def _impl(ctx):
         tool_path(name = "nm", path = "NOT_USED"),
         tool_path(name = "objdump", path = "/bin/false"),
         tool_path(name = "strip", path = "NOT_USED"),
+        tool_path(name = "dwp", path = emdwp_script),
     ]
 
     ################################################################
@@ -460,6 +464,34 @@ def _impl(ctx):
         feature(
             name = "wasm_standalone",
         ),
+        # Support for debug fission. In short, debugging fission should:
+        #   * reduce linking time, RAM usage and disk usage  
+        #   * speed up incremental builds
+        #   * speed up debugger work (reduce startup and breakpoint time)
+        # (to use this, follow the --fission=yes flag)
+        # https://developer.chrome.com/blog/faster-wasm-debugging
+        # https://bazel.build/docs/user-manual#fission
+        feature(
+            name = "per_object_debug_info",
+            flag_sets = [
+                flag_set(
+                    actions = [
+                        ACTION_NAMES.c_compile,
+                        ACTION_NAMES.cpp_compile,
+                        ACTION_NAMES.cpp_module_codegen,
+                        ACTION_NAMES.assemble,
+                        ACTION_NAMES.preprocess_assemble,
+                    ],
+                    flag_groups = [
+                        flag_group(
+                            flags = ["-g", "-gsplit-dwarf", "-gdwarf-5", "-gpubnames"],
+                            expand_if_available = "per_object_debug_info_file",
+                        ),
+                    ],
+                ),
+            ],
+            enabled = True,
+        ),
     ]
 
     crosstool_default_flag_sets = [

bazel/emscripten_toolchain/wasm_cc_binary.bzl

@@ -129,12 +129,17 @@ def _wasm_cc_binary_impl(ctx):
         executable = ctx.executable._wasm_binary_extractor,
     )
 
+    outputs = ctx.outputs.outputs
+    dwp_file = cc_target[DebugPackageInfo].dwp_file if DebugPackageInfo in cc_target else None
+    if dwp_file:
+        outputs = outputs + [dwp_file]
+
     return [
         DefaultInfo(
-            files = depset(ctx.outputs.outputs),
+            files = depset(outputs),
             # This is needed since rules like web_test usually have a data
             # dependency on this target.
-            data_runfiles = ctx.runfiles(transitive_files = depset(ctx.outputs.outputs)),
+            data_runfiles = ctx.runfiles(transitive_files = depset(outputs)),
         ),
         OutputGroupInfo(_wasm_tar = cc_target.files),
     ]
@@ -167,6 +172,10 @@ def _wasm_cc_binary_legacy_impl(ctx):
         executable = ctx.executable._wasm_binary_extractor,
     )
 
+    dwp_file = cc_target[DebugPackageInfo].dwp_file if DebugPackageInfo in cc_target else None
+    if dwp_file:
+        outputs = outputs + [dwp_file]
+
     return [
         DefaultInfo(
             executable = ctx.outputs.wasm,