StringLowering: Escape the JSON in the custom section

src/passes/StringLowering.cpp

@@ -37,7 +37,7 @@
 #include "ir/type-updating.h"
 #include "ir/utils.h"
 #include "pass.h"
-#include "support/json.h"
+#include "support/string.h"
 #include "wasm-builder.h"
 #include "wasm.h"
 
@@ -205,8 +205,9 @@ struct StringLowering : public StringGathering {
 
   void makeImports(Module* module) {
     Index importIndex = 0;
-    json::Value stringArray;
-    stringArray.setArray();
+    std::stringstream json;
+    json << '[';
+    bool first = true;
     std::vector<Name> importedStrings;
     for (auto& global : module->globals) {
       if (global->init) {
@@ -216,16 +217,19 @@ struct StringLowering : public StringGathering {
           importIndex++;
           global->init = nullptr;
 
-          auto str = json::Value::make(std::string(c->string.str).c_str());
-          stringArray.push_back(str);
+          if (first) {
+            first = false;
+          } else {
+            json << ',';
+          }
+          String::printEscaped(json, c->string.str, String::EscapeMode::JSON);
         }
       }
     }
 
     // Add a custom section with the JSON.
-    std::stringstream stream;
-    stringArray.stringify(stream);
-    auto str = stream.str();
+    json << ']';
+    auto str = json.str();
     auto vec = std::vector<char>(str.begin(), str.end());
     module->customSections.emplace_back(
       CustomSection{"string.consts", std::move(vec)});

src/support/json.cpp

@@ -15,13 +15,15 @@
  */
 
 #include "support/json.h"
+#include "support/string.h"
 
 namespace json {
 
 void Value::stringify(std::ostream& os, bool pretty) {
   if (isString()) {
-    // TODO: escaping
-    os << '"' << getCString() << '"';
+    wasm::String::printEscaped(os,
+                               getCString(),
+                               wasm::String::EscapeMode::JSON);
   } else if (isArray()) {
     os << '[';
     auto first = true;

src/support/string.cpp

@@ -106,7 +106,7 @@ std::string trim(const std::string& input) {
   return input.substr(0, size);
 }
 
-std::ostream& printEscaped(std::ostream& os, std::string_view str) {
+std::ostream& printEscaped(std::ostream& os, std::string_view str, EscapeMode mode) {
   os << '"';
   for (unsigned char c : str) {
     switch (c) {
@@ -132,7 +132,13 @@ std::ostream& printEscaped(std::ostream& os, std::string_view str) {
         if (c >= 32 && c < 127) {
           os << c;
         } else {
-          os << std::hex << '\\' << (c / 16) << (c % 16) << std::dec;
+          if (mode == EscapeMode::Normal) {
+            os << std::hex << '\\' << (c / 16) << (c % 16) << std::dec;
+          } else if (mode == EscapeMode::JSON) {
+            os << std::hex << "\\u00" << (c / 16) << (c % 16) << std::dec;
+          } else {
+            WASM_UNREACHABLE("bad mode");
+          }
         }
       }
     }

src/support/string.h

@@ -75,7 +75,14 @@ inline bool isNumber(const std::string& str) {
   return !str.empty() && std::all_of(str.begin(), str.end(), ::isdigit);
 }
 
-std::ostream& printEscaped(std::ostream& os, std::string_view str);
+enum EscapeMode {
+  Normal,
+  JSON
+};
+
+std::ostream& printEscaped(std::ostream& os,
+                           std::string_view str,
+                           EscapeMode mode = Normal);
 
 } // namespace wasm::String
 

test/lit/passes/string-lowering.js

@@ -0,0 +1,6 @@
+var filename = process.argv[2];
+var module = new WebAssembly.Module(require('fs').readFileSync(filename));
+var sections = WebAssembly.Module.customSections(module, 'string.consts');
+var array = new Uint8Array(sections[0]);
+var string = new TextDecoder('utf-8').decode(array);
+console.log("JSON:", string);

test/lit/passes/string-lowering.wast

@@ -2,8 +2,6 @@
 ;; operations are tested in string-gathering.wast (which is auto-updated, unlike
 ;; this which is manual).
 
-;; RUN: foreach %s %t wasm-opt --string-lowering -all -S -o - | filecheck %s
-
 (module
   (func $consts
     (drop
@@ -15,9 +13,25 @@
     (drop
       (string.const "foo")
     )
+    (drop
+      (string.const "needs\tescaping\00.")
+    )
   )
 )
 
-;; The custom section should contain foo and bar, and foo only once.
-;; CHECK: custom section "string.consts", size 13, contents: "[\"bar\",\"foo\"]"
+;; The custom section should contain foo and bar, and foo only once, and the
+;; string with \t should be escaped.
+;;
+;; RUN: wasm-opt %s --string-lowering -all -S -o - | filecheck %s
+;;
+;; CHECK: custom section "string.consts", size 38, contents: "[\"bar\",\"foo\",\"needs\\tescaping\\u0000.\"]"
+
+;; The custom section should parse OK using JSON.parse from node.
+;; (Note we run --remove-unused-module-elements to remove externref-using
+;; imports, which require a newer version of node.)
+;;
+;; RUN: wasm-opt %s --string-lowering --remove-unused-module-elements -all -o %t.wasm
+;; RUN: node %S/string-lowering.js %t.wasm | filecheck %s --check-prefix=CHECK-JS
+;;
+;; CHECK-JS: JSON: ["bar","foo","needs\tescaping\u0000."]