Add header TOC generation

Fix Issue 18202 - Show TOC overview in the dlang specification pages

ddoc.d

@@ -14,7 +14,9 @@ Example usage:
 
 Author: Sebastian Wilzbach
 */
-import std.stdio;
+import std.algorithm, std.array, std.ascii, std.conv, std.file, std.functional,
+        std.meta, std.path, std.range, std.string, std.typecons;
+import std.stdio : writeln, writefln;
 
 struct Config
 {
@@ -45,6 +47,10 @@ int main(string[] args)
 
     import std.file : readText;
     auto text = args[$ - 1].readText;
+
+    // transform and extend the ddoc page
+    text = genHeader(text);
+
     return compile(text, args[1 .. $ - 1]);
 }
 
@@ -58,3 +64,117 @@ auto compile(R)(R buffer, string[] arguments)
     pipes.stdin.close;
     return wait(pipes.pid);
 }
+
+// replaces the content of a DDoc macro call
+auto updateDdocTag(string fileText, string ddocKey, string newContent)
+{
+    auto pos = fileText.representation.countUntil(ddocKey);
+    if (pos < 0)
+        return fileText;
+    const ddocStartLength = ddocKey.representation.until('(', No.openRight).count;
+    auto len = fileText[pos .. $].representation.drop(ddocStartLength).untilClosingParentheses.walkLength;
+    return fileText.replace(fileText[pos .. pos + len + ddocStartLength + 1], newContent);
+}
+
+// a range until the next ')', nested () are ignored
+auto untilClosingParentheses(R)(R rs)
+{
+    return rs.cumulativeFold!((count, r){
+        switch(r)
+        {
+            case '(':
+                count++;
+                break;
+            case ')':
+                count--;
+                break;
+            default:
+        }
+        return count;
+    })(1).zip(rs).until!(e => e[0] == 0).map!(e => e[1]);
+}
+
+unittest
+{
+    import std.algorithm.comparison : equal;
+    assert("aa $(foo $(bar)foobar)".untilClosingParentheses.equal("aa $(foo $(bar)foobar)"));
+    assert("$(FOO a, b, $(ARGS e, f)))".untilClosingParentheses.equal("$(FOO a, b, $(ARGS e, f))"));
+}
+
+// parse the ddoc file for H2 and H3 items
+// H3 items are listed as subitems
+auto parseToc(string text)
+{
+    alias TocEntry = Tuple!(string, "id", string, "name");
+    alias TocTopEntry = Tuple!(TocEntry, "main", TocEntry[], "children");
+    TocTopEntry[] toc;
+
+    bool isH2 = true;
+    void append(string id, string name)
+    {
+        auto entry = TocEntry(id, name);
+        if (isH2)
+            toc ~= TocTopEntry(entry, null);
+        else
+            toc.back.children ~= entry;
+    }
+    while (!text.empty)
+    {
+        enum needles = AliasSeq!("$(H2 ", "$(SECTION2 ", "$(H3", "$(SECTION3");
+        auto res = text.find(needles);
+        if (res[0].empty)
+            break;
+
+        isH2 = res[1] <= 2;
+        text = res[0].drop(needles.only[res[1] - 1].length);
+        text.skipOver!isWhite;
+
+        enum gname = "$(GNAME ";
+        enum lNameNeedles = AliasSeq!("$(LNAME2", "$(LEGACY_LNAME2");
+        if (text.startsWith(gname))
+        {
+            auto name = text.drop(gname.length).untilClosingParentheses.to!string.strip;
+            append(name, name);
+        }
+        else if (auto idx = text.startsWith(lNameNeedles))
+        {
+            auto arr = text.drop(lNameNeedles.only[idx - 1].length).splitter(",");
+            if (idx == 2)
+                arr.popFront;
+            append(arr.front.strip, arr.dropOne.joiner(",").untilClosingParentheses.to!string.strip);
+        }
+    }
+    return toc;
+}
+
+// Ddoc splits arguments by commas
+auto escapeDdoc(string s)
+{
+    return s.replace(",", "$(COMMA)");
+}
+
+// generated a SPEC_HEADERNAV_TOC Ddoc macro with the parsed H2/H3 entries
+auto genHeader(string fileText)
+{
+    enum ddocKey = "$(SPEC_HEADERNAV_TOC";
+    auto newContent = ddocKey ~ "\n";
+    enum indent = "    ";
+    foreach (entry; fileText.parseToc)
+    {
+        if (entry.children)
+        {
+            newContent ~= "%s$(SPEC_HEADERNAV_SUBITEMS %s, %s,\n".format(indent, entry.main.id, entry.main.name.escapeDdoc);
+            foreach (child; entry.children)
+                newContent ~= "%s$(SPEC_HEADERNAV_ITEM %s, %s)\n".format(indent.repeat(2).joiner, child.id, child.name.escapeDdoc);
+            newContent ~= indent;
+            newContent ~= ")\n";
+        }
+        else
+        {
+            newContent ~= "%s$(SPEC_HEADERNAV_ITEM %s, %s)\n".format(indent, entry.main.id, entry.main.name.escapeDdoc);
+        }
+    }
+    newContent ~= ")";
+    return updateDdocTag(fileText, ddocKey, newContent);
+}
+