Save build ID in a source map (#6799)

This is based on these two proposals:

 * https://github.com/WebAssembly/tool-conventions/blob/main/BuildId.md
 * https://github.com/tc39/source-map/blob/main/proposals/debug-id.md

src/wasm-binary.h

@@ -414,6 +414,7 @@ extern const char* Dylink;
 extern const char* Dylink0;
 extern const char* Linking;
 extern const char* Producers;
+extern const char* BuildId;
 extern const char* TargetFeatures;
 
 extern const char* AtomicsFeature;

src/wasm/wasm-binary.cpp

@@ -16,6 +16,7 @@
 
 #include <algorithm>
 #include <fstream>
+#include <iomanip>
 
 #include "ir/eh-utils.h"
 #include "ir/module-utils.h"
@@ -1212,7 +1213,31 @@ void WasmBinaryWriter::initializeDebugInfo() {
 }
 
 void WasmBinaryWriter::writeSourceMapProlog() {
-  *sourceMap << "{\"version\":3,\"sources\":[";
+  *sourceMap << "{\"version\":3,";
+
+  for (const auto& section : wasm->customSections) {
+    if (section.name == BinaryConsts::CustomSections::BuildId) {
+      U32LEB ret;
+      size_t pos = 0;
+      ret.read([&]() { return section.data[pos++]; });
+
+      if (section.data.size() != pos + ret.value) {
+        std::cerr
+          << "warning: build id section with an incorrect size detected!\n";
+        break;
+      }
+
+      *sourceMap << "\"debugId\":\"";
+      for (size_t i = pos; i < section.data.size(); i++) {
+        *sourceMap << std::setfill('0') << std::setw(2) << std::hex
+                   << static_cast<int>(static_cast<uint8_t>(section.data[i]));
+      }
+      *sourceMap << "\",";
+      break;
+    }
+  }
+
+  *sourceMap << "\"sources\":[";
   for (size_t i = 0; i < wasm->debugInfoFileNames.size(); i++) {
     if (i > 0) {
       *sourceMap << ",";

src/wasm/wasm.cpp

@@ -36,6 +36,7 @@ const char* Dylink = "dylink";
 const char* Dylink0 = "dylink.0";
 const char* Linking = "linking";
 const char* Producers = "producers";
+const char* BuildId = "build_id";
 const char* TargetFeatures = "target_features";
 const char* AtomicsFeature = "atomics";
 const char* BulkMemoryFeature = "bulk-memory";

test/lit/binary/custom-section-build-id.test

@@ -0,0 +1,7 @@
+# Verify that the build id is included in the source map.
+
+;; RUN: wasm-opt %s.wasm -o %t.wasm -osm %t.map
+;; RUN: cat %t.map | filecheck %s
+
+;; CHECK: {"version":3,"debugId":"01ab23cd45ef67ab89","sources":[],"names":[],"mappings":""}
+