fix: expr/edge-casesテストを修正

- 連続+演算子を正しくパース（1 + + 2 → 3）
- エラーメッセージをWikidot互換に変更（too many values in the stack）
- ifexprエラー時にエラーメッセージを出力（elseブランチではなく）
- 空式で段落を分割するポストプロセス処理を追加

Author: r74tech

packages/parser/src/parser/postprocess/spanStrip.ts

@@ -2,8 +2,9 @@
  * Post-processing for parsed AST
  *
  * Handles span_ (paragraph strip) paragraph merging
+ * Handles empty expr splitting paragraphs
  */
-import type { Element, ContainerData } from "@wdprlib/ast";
+import type { Element, ContainerData, ExprData } from "@wdprlib/ast";
 
 /**
  * Check if an element is a container with specific type
@@ -226,6 +227,77 @@ function splitParagraphAtBlankLineSpans(para: Element): Element[] {
   return result.length > 0 ? result : [para];
 }
 
+/**
+ * Check if an element is an empty expr (expression is empty string)
+ */
+function isEmptyExpr(el: Element): boolean {
+  if (el.element !== "expr") return false;
+  const data = el.data as ExprData;
+  return data.expression === "";
+}
+
+/**
+ * Split paragraph at empty expr elements
+ * Empty expr acts as a paragraph break
+ * Returns array of paragraphs (original may be split into multiple)
+ */
+function splitParagraphAtEmptyExpr(para: Element): Element[] {
+  const data = getContainerData(para);
+  if (!data || data.type !== "paragraph") return [para];
+
+  // Check if paragraph contains empty expr
+  const hasEmptyExpr = data.elements.some(isEmptyExpr);
+  if (!hasEmptyExpr) return [para];
+
+  const result: Element[] = [];
+  let currentElements: Element[] = [];
+
+  for (let i = 0; i < data.elements.length; i++) {
+    const child = data.elements[i];
+    if (!child) continue;
+
+    if (isEmptyExpr(child)) {
+      // Skip the empty expr and surrounding line-breaks
+      // Check if prev element is line-break, remove it
+      if (currentElements.length > 0 && currentElements[currentElements.length - 1]?.element === "line-break") {
+        currentElements.pop();
+      }
+      // Save current paragraph if not empty
+      if (currentElements.length > 0) {
+        result.push({
+          element: "container",
+          data: {
+            type: "paragraph",
+            attributes: {},
+            elements: currentElements,
+          },
+        });
+        currentElements = [];
+      }
+      // Skip next line-break if present
+      if (i + 1 < data.elements.length && data.elements[i + 1]?.element === "line-break") {
+        i++;
+      }
+    } else {
+      currentElements.push(child);
+    }
+  }
+
+  // Add remaining elements as final paragraph
+  if (currentElements.length > 0) {
+    result.push({
+      element: "container",
+      data: {
+        type: "paragraph",
+        attributes: {},
+        elements: currentElements,
+      },
+    });
+  }
+
+  return result.length > 0 ? result : [];
+}
+
 /**
  * Merge consecutive paragraphs that contain span_ (paragraph strip mode)
  * Wikidot behavior: span_ removes paragraph breaks around it
@@ -237,15 +309,18 @@ function splitParagraphAtBlankLineSpans(para: Element): Element[] {
  * outside the paragraph.
  *
  * Also splits paragraphs containing spans with _splitByBlankLine marker.
+ * Also splits paragraphs at empty [[#expr ]] elements.
  */
 export function mergeSpanStripParagraphs(children: Element[]): Element[] {
-  // First pass: split paragraphs at _splitByBlankLine markers
+  // First pass: split paragraphs at _splitByBlankLine markers and empty expr
   const expandedChildren: Element[] = [];
   for (const child of children) {
     if (isContainer(child, "paragraph")) {
       const data = getContainerData(child);
       if (data && data.elements.some(isSplitSpan)) {
         expandedChildren.push(...splitParagraphAtBlankLineSpans(child));
+      } else if (data && data.elements.some(isEmptyExpr)) {
+        expandedChildren.push(...splitParagraphAtEmptyExpr(child));
       } else {
         expandedChildren.push(child);
       }

packages/render/src/elements/expr.ts

@@ -28,13 +28,17 @@ export function renderIf(ctx: RenderContext, data: IfCondData): void {
 
 /**
  * Render #ifexpr - evaluates expression and branches based on result
- * On error, selects else branch (Wikidot-compatible)
+ * On error, outputs Wikidot-compatible error message
  */
 export function renderIfExpr(ctx: RenderContext, data: IfExprData): void {
   const result = evaluateExpression(data.expression);
-  // ifexpr: error or 0 selects else branch
-  const isTrue = result.success && result.value !== 0;
-  const elements = isTrue ? data.then : data.else;
+  if (!result.success) {
+    // ifexpr: error outputs error message (Wikidot-compatible)
+    ctx.pushEscaped(`run-time error: ${result.error}`);
+    return;
+  }
+  // 0 selects else branch, non-zero selects then branch
+  const elements = result.value !== 0 ? data.then : data.else;
   renderBranchElements(ctx, elements);
 }
 

packages/render/src/utils/expr-eval.ts

@@ -238,7 +238,8 @@ class ExprParser {
   parse(): number {
     const result = this.parseOr();
     if (this.current().kind !== "EOF") {
-      throw new Error("Unexpected token");
+      // Wikidot-compatible error message when extra values remain
+      throw new Error("too many values in the stack");
     }
     return result;
   }
@@ -386,7 +387,7 @@ class ExprParser {
     }
     if (kind === "PLUS") {
       this.advance();
-      return this.parseUnary();
+      return +this.parseUnary();
     }
 
     return this.parsePrimary();

tests/fixtures/expr/edge-cases/expected.json

@@ -38,19 +38,16 @@
             "data": {
               "expression": "1 + + 2"
             }
-          },
-          {
-            "element": "line-break"
-          },
-          {
-            "element": "expr",
-            "data": {
-              "expression": ""
-            }
-          },
-          {
-            "element": "line-break"
-          },
+          }
+        ]
+      }
+    },
+    {
+      "element": "container",
+      "data": {
+        "type": "paragraph",
+        "attributes": {},
+        "elements": [
           {
             "element": "expr",
             "data": {

tests/integration/fixture-render.test.ts

@@ -19,7 +19,7 @@ const EXCLUDED_FIXTURES = new Set<string>([
   "module/listusers/fail", // 同上
   "module/pagetree", // PageTreeは動的コンテンツ（resolver未実装）
   "table/fail-paragraph", // リンク解釈・段落内改行処理の問題（別issueで対応）
-  "expr/edge-cases", // エラーメッセージがWikidotと異なる（スタックベース vs 再帰下降）
+  // "expr/edge-cases", // エラーメッセージがWikidotと異なる（スタックベース vs 再帰下降）
   "misc/bibliography", // bibliography機能（bibcite/bibitems）が未実装
 ]);