Bound embedded source literals for MSVC

docs/validation/msvc-embedded-source-literals-690.md

@@ -0,0 +1,24 @@
+# MSVC embedded source literal portability
+
+Issue #690 repairs the Windows NuGet run 35449781793 failures where MSVC
+reported C2026 for hand-authored JavaScript embedded in the stylesheet CSSOM,
+cache/frame and File System Access sources. Their largest individual raw
+literals were 83,590, 16,956 and 38,859 bytes respectively, above MSVC's
+16,380-byte string-literal limit.
+
+Each program is now an ordered array of raw-literal views whose individual
+parts stay below a conservative 15,000-byte ceiling. The reusable source
+contract checks that ceiling at compile time. The join helper reserves the
+exact total size and concatenates each array once at realm installation,
+without separators, so V8 receives the same program bytes in one compile and
+run operation. The split does not add per-frame work or retained duplicate
+payloads.
+
+The stylesheet CSSOM JavaScript contract reconstructs the array in declaration
+order before exercising the existing browser-facing behavior. Future edits
+must add another part before any literal crosses the shared ceiling. The
+compiler-generated-file incident from the same Windows job remains outside
+this issue.
+
+Only `git diff --check` was run under the directed fast policy. Windows package
+compilation and the existing runtime contracts remain for CI.

experiments/WebScene.NativeEngine.Probe/native/webscene_embedded_source.h

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <array>
+#include <cstddef>
+#include <limits>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+
+namespace webscene_native {
+
+// MSVC rejects a single string literal above 16,380 bytes. Keep enough
+// headroom for source encoding while allowing larger programs to be assembled
+// once, in declaration order, without separators.
+inline constexpr std::size_t maximum_portable_embedded_source_literal_bytes =
+    15'000U;
+
+template<std::size_t Count>
+constexpr bool embedded_source_parts_are_portable(
+    const std::array<std::string_view, Count>& parts) noexcept
+{
+    for (const auto part : parts) {
+        if (part.size() > maximum_portable_embedded_source_literal_bytes) {
+            return false;
+        }
+    }
+    return true;
+}
+
+template<std::size_t Count>
+std::string join_embedded_source_parts(
+    const std::array<std::string_view, Count>& parts)
+{
+    std::size_t source_size = 0U;
+    for (const auto part : parts) {
+        if (part.size() > std::numeric_limits<std::size_t>::max() - source_size) {
+            throw std::length_error("embedded source size overflow");
+        }
+        source_size += part.size();
+    }
+
+    std::string source;
+    source.reserve(source_size);
+    for (const auto part : parts) source.append(part);
+    return source;
+}
+
+} // namespace webscene_native

experiments/WebScene.NativeEngine.Probe/native/webscene_stylesheet_cssom_compatibility.h

@@ -1,5 +1,5 @@
 #pragma once
-#include <string_view>
+#include "webscene_embedded_source.h"
 
 namespace webscene_native {
 // The pinned WebScene exposes a stable native HTMLStyleElement.sheet object,
@@ -10,7 +10,7 @@ namespace webscene_native {
 // Imported sheets use the host stylesheet loader and keep their authored CSSOM
 // tree separate from the flattened native publication payload.
 // Semantics: https://www.w3.org/TR/cssom-1/
-inline constexpr std::string_view cssCompatibilityScript = R"JS(
+inline constexpr std::array<std::string_view, 7> cssCompatibilityScriptParts{R"JS(
 // SCENETECH_CSS_COMPATIBILITY_V1
 (() => {
   'use strict';
@@ -255,7 +255,8 @@ inline constexpr std::string_view cssCompatibilityScript = R"JS(
         cursor = index + 1;
         continue;
       }
-      if (!atEnd && character === '{') {
+)JS",
+R"JS(      if (!atEnd && character === '{') {
         const prelude = source.slice(cursor, index).trim();
         if (!prelude) exception('A nested rule requires a prelude', 'SyntaxError');
         flushDeclarations();
@@ -527,7 +528,8 @@ inline constexpr std::string_view cssCompatibilityScript = R"JS(
             else if (character === quote) quote = '';
             continue;
           }
-          if (character === '"' || character === "'") { quote = character; continue; }
+)JS",
+R"JS(          if (character === '"' || character === "'") { quote = character; continue; }
           if (character === '(') parentheses++;
           else if (character === ')' && parentheses) parentheses--;
           else if (character === '[') brackets++;
@@ -821,7 +823,8 @@ inline constexpr std::string_view cssCompatibilityScript = R"JS(
     const identifier = /^(-?[_a-zA-Z][_a-zA-Z0-9-]*)\s+/.exec(source);
     if (identifier) {
       prefix = identifier[1];
-      source = source.slice(identifier[0].length).trim();
+)JS",
+R"JS(      source = source.slice(identifier[0].length).trim();
     }
     let namespaceURI = '';
     if (source[0] === '"' || source[0] === "'") {
@@ -1098,7 +1101,8 @@ inline constexpr std::string_view cssCompatibilityScript = R"JS(
         }
       }
       if (loaded?.url) resolvedHref = String(loaded.url);
-      ancestors.add(resolvedHref);
+)JS",
+R"JS(      ancestors.add(resolvedHref);
       childState = {
         sheet: childSheet,
         owner: null,
@@ -1382,7 +1386,8 @@ inline constexpr std::string_view cssCompatibilityScript = R"JS(
           if (attached()) publish(state);
           return index;
         } },
-        deleteRule: { writable: true, value(index) {
+)JS",
+R"JS(        deleteRule: { writable: true, value(index) {
           if (arguments.length === 0) throw new TypeError('A rule index is required');
           synchronize(state);
           index = Number(index) >>> 0;
@@ -1677,7 +1682,8 @@ inline constexpr std::string_view cssCompatibilityScript = R"JS(
           }
         }
       },
-      insertRule: { configurable: true, writable: true, value(rule, index = 0) {
+)JS",
+R"JS(      insertRule: { configurable: true, writable: true, value(rule, index = 0) {
         if (arguments.length === 0) throw new TypeError('A CSS rule is required');
         const current = stateFor(this);
         index = Number(index) >>> 0;
@@ -1950,5 +1956,6 @@ inline constexpr std::string_view cssCompatibilityScript = R"JS(
     value: augment, configurable: true
   });
 })();
-)JS";
+)JS"};
+static_assert(embedded_source_parts_are_portable(cssCompatibilityScriptParts));
 }

experiments/WebScene.NativeEngine.Probe/native/webscene_v8_runtime_cache_and_frames.inc

@@ -1529,7 +1529,7 @@
         // realm-local and route delivery through this frame's setTimeout so a
         // posted message is a serialized browser task rather than a nested V8
         // call. This mirrors the working managed V8 iframe implementation.
-        constexpr std::string_view message_channel_source = R"JS(
+        constexpr std::array<std::string_view, 3> message_channel_source_parts{R"JS(
             (() => {
               class MessagePort {
                 constructor() {
@@ -1735,8 +1735,8 @@
                     `${encode(name)}=${encode(value)}`).join('&');
                 }
               }
-        )JS";
-        constexpr std::string_view message_channel_source_suffix = R"JS(
+        )JS",
+        R"JS(
               class WebSceneFormData {
                 constructor(form = undefined, submitter = null) {
                   __webSceneRecordWebApi(
@@ -1945,7 +1945,8 @@
                     HierarchyRequestError: 3,
                     WrongDocumentError: 4,
                     InvalidCharacterError: 5,
-                    NoModificationAllowedError: 7,
+)JS",
+        R"JS(                    NoModificationAllowedError: 7,
                     NotFoundError: 8,
                     NotSupportedError: 9,
                     InUseAttributeError: 10,
@@ -2046,12 +2047,10 @@
                 }
               });
             })();
-        )JS";
-        std::string message_channel_bootstrap;
-        message_channel_bootstrap.reserve(
-            message_channel_source.size() + message_channel_source_suffix.size());
-        message_channel_bootstrap.append(message_channel_source);
-        message_channel_bootstrap.append(message_channel_source_suffix);
+        )JS"};
+        static_assert(embedded_source_parts_are_portable(message_channel_source_parts));
+        auto message_channel_bootstrap =
+            join_embedded_source_parts(message_channel_source_parts);
         auto message_channel_script = v8::Script::Compile(
             local_context,
             js_string(isolate, message_channel_bootstrap.c_str())).ToLocalChecked();

experiments/WebScene.NativeEngine.Probe/native/webscene_v8_runtime_file_system_access.inc

@@ -1335,7 +1335,7 @@
             js_string(isolate, "__webSceneFileSystemHandleState"),
             v8::Function::New(local_context, file_system_handle_state)
                 .ToLocalChecked()).Check();
-        constexpr std::string_view source = R"JS(
+        constexpr std::array<std::string_view, 4> source_parts{R"JS(
           (() => {
             const requestPanel = globalThis.__webSceneRequestFilePanel;
             const compareGrants = globalThis.__webSceneCompareFileGrants;
@@ -1564,7 +1564,8 @@
             };
             const queueWriterCommand = (stream, command) => {
               if (!writerStates.has(stream)) {
-                return Promise.reject(new TypeError('Illegal invocation'));
+)JS",
+        R"JS(                return Promise.reject(new TypeError('Illegal invocation'));
               }
               let writer;
               try { writer = WritableStream.prototype.getWriter.call(stream); }
@@ -1819,7 +1820,8 @@
                 value: keys },
               values: { enumerable: true, configurable: true, writable: true,
                 value: values },
-              [Symbol.asyncIterator]: { configurable: true, writable: true,
+)JS",
+        R"JS(              [Symbol.asyncIterator]: { configurable: true, writable: true,
                 value: entries },
               getFileHandle: { enumerable: true, configurable: true, writable: true,
                 value: getFileHandle },
@@ -2065,7 +2067,8 @@
                 return { description: String(type.description || ''), accept };
               });
             };
-            const normalize = (kind, options) => {
+)JS",
+        R"JS(            const normalize = (kind, options) => {
               if (options == null) options = {};
               if (typeof options !== 'object') throw new TypeError('Picker options must be an object');
               const types = kind === 2 ? [] : normalizeTypes(options.types);
@@ -2117,10 +2120,12 @@
                 writable: true, value: showSaveFilePicker }
             });
           })();
-        )JS";
+        )JS"};
+        static_assert(embedded_source_parts_are_portable(source_parts));
+        auto source = join_embedded_source_parts(source_parts);
         auto script = v8::Script::Compile(
             local_context,
-            js_string(isolate, std::string(source).c_str())).ToLocalChecked();
+            js_string(isolate, source.c_str())).ToLocalChecked();
         script->Run(local_context).ToLocalChecked();
     }
     static constexpr std::size_t maximum_file_system_handle_bindings = 16384U;

experiments/WebScene.NativeEngine.Probe/native/webscene_v8_runtime_web_api_compatibility.inc

@@ -55,8 +55,10 @@
             local_context,
             "FileReader",
             fileReaderCompatibilityScript);
+        const auto css_compatibility_script =
+            join_embedded_source_parts(cssCompatibilityScriptParts);
         install_web_api_compatibility_script(
             local_context,
             "stylesheet CSSOM",
-            cssCompatibilityScript);
+            css_compatibility_script);
     }

tests/RuntimeCompatibility/stylesheet-cssom.test.mjs

@@ -5,8 +5,11 @@ import { performance as nodePerformance } from 'node:perf_hooks';
 import { createContext, runInContext } from 'node:vm';
 
 const header = readFileSync(new URL('../../experiments/WebScene.NativeEngine.Probe/native/webscene_stylesheet_cssom_compatibility.h', import.meta.url), 'utf8');
-const script = header.match(/cssCompatibilityScript = R"JS\(([\s\S]*?)\)JS";/)?.[1];
-assert.ok(script, 'native CSS compatibility script must be embedded');
+const scriptDeclaration = header.match(
+  /cssCompatibilityScriptParts\{([\s\S]*?)\};\nstatic_assert/)?.[1];
+assert.ok(scriptDeclaration, 'native CSS compatibility script parts must be embedded');
+const script = Array.from(scriptDeclaration.matchAll(/R"JS\(([\s\S]*?)\)JS"/g), match => match[1]).join('');
+assert.ok(script, 'native CSS compatibility script must be reconstructable');
 assert.equal(/<\/script/i.test(script), false, 'script must be safe to embed in HTML');
 
 function setup() {