scanTagURI now scans to a slice, as does scanURIEscapes, at cost of complexity

source/dyaml/scanner.d

@@ -991,13 +991,13 @@ final class Scanner
             return value;
         }
 
-        ///Scan prefix of a tag directive.
+        /// Scan prefix of a tag directive.
-        dchar[] scanTagDirectivePrefix(const Mark startMark) @safe pure
+        dstring scanTagDirectivePrefix(const Mark startMark) @safe pure
         {
             auto value = scanTagURI("directive", startMark);
             enforce(" \0\n\r\u0085\u2028\u2029"d.canFind(reader_.peek()),
                     new Error("While scanning a directive prefix", startMark,
-                              "expected ' ', but found" ~ to!string(reader_.peek()),
+                              "expected ' ', but found" ~ reader_.peek().to!string,
                               reader_.mark));
 
             return value;
@@ -1054,13 +1054,13 @@ final class Scanner
             assert(false, "This code should never be reached");
         }
 
-        ///Scan a tag token.
+        /// Scan a tag token.
-        Token scanTag() @safe pure
+        Token scanTag() @trusted pure
         {
             const startMark = reader_.mark;
             dchar c = reader_.peek(1);
-            dchar[] handle;
+            dstring handle;
-            dchar[] suffix;
+            dstring suffix;
 
             if(c == '<')
             {
@@ -1699,48 +1699,80 @@ final class Scanner
         }
 
         /// Scan URI in a tag token.
-        dchar[] scanTagURI(const string name, const Mark startMark) @trusted pure
+        dstring scanTagURI(const string name, const Mark startMark) @trusted pure
         {
             // Note: we do not check if URI is well-formed.
-            // Using appender_, so clear it when we're done.
-            scope(exit) { appender_.clear(); }
-            uint length = 0;
 
+            reader_.sliceBuilder.begin();
             dchar c = reader_.peek();
+            {
+                scope(failure) { reader_.sliceBuilder.finish(); }
+                uint length = 0;
                 while(isAlphaNum(c) || "-;/?:@&=+$,_.!~*\'()[]%"d.canFind(c))
                 {
                     if(c == '%')
                     {
-                    appender_.put(reader_.get(length));
+                        auto chars = reader_.get(length);
+                        reader_.sliceBuilder.write(chars);
                         length = 0;
-                    appender_.put(scanURIEscapes(name, startMark));
+                        scanURIEscapesToSlice(name, startMark);
                     }
                     else { ++length; }
                     c = reader_.peek(length);
                 }
                 if(length > 0)
                 {
-                appender_.put(reader_.get(length));
+                    auto chars = reader_.get(length);
+                    reader_.sliceBuilder.write(chars);
                     length = 0;
                 }
-            enforce(appender_.data.length > 0,
+            }
+            dstring result = reader_.sliceBuilder.finish();
+            enforce(!result.empty,
                     new Error("While parsing a " ~ name, startMark,
                               "expected URI, but found: " ~ c.to!string, reader_.mark));
 
-            return appender_.data;
+            return result;
         }
 
         /// Scan URI escape sequences.
-        dchar[] scanURIEscapes(const string name, const Mark startMark) @system pure
+        void scanURIEscapesToSlice(const string name, const Mark startMark) @system pure
         {
-            ubyte[] bytes;
+            // URI escapes encode a UTF-8 string. We store UTF-8 code units here for
+            // decoding into UTF-32.
+            char[4] bytes;
+            size_t bytesUsed;
             Mark mark = reader_.mark;
 
+            // Get one dchar by decoding data from bytes.
+            //
+            // This is probably slow, but simple and URI escapes are extremely uncommon
+            // in YAML.
+            static size_t getDchar(char[] bytes, Reader reader_)
+            {
+                import std.utf;
+                size_t nextChar;
+                const c = std.utf.decode(bytes[], nextChar); 
+                reader_.sliceBuilder.write(c);
+                if(bytes.length - nextChar > 0)
+                {
+                    core.stdc.string.memmove(bytes.ptr, bytes.ptr + nextChar, 
+                                             bytes.length - nextChar);
+                }
+                return bytes.length - nextChar;
+            }
+
+            try 
+            {
                 while(reader_.peek() == '%')
                 {
                     reader_.forward();
+                    if(bytesUsed == bytes.length)
+                    {
+                        bytesUsed = getDchar(bytes[], reader_); 
+                    }
 
-                ubyte b = 0;
+                    char b = 0;
                     uint mult = 16;
                     // Converting 2 hexadecimal digits to a byte.
                     foreach(k; 0 .. 2)
@@ -1760,15 +1792,12 @@ final class Scanner
                         b += mult * digit;
                         mult /= 16;
                     }
-                bytes ~= b;
+                    bytes[bytesUsed++] = b;
 
                     reader_.forward(2);
                 }
 
-            try { return to!(dchar[])(cast(string)bytes); }
+                bytesUsed = getDchar(bytes[0 .. bytesUsed], reader_);
-            catch(ConvException e)
-            {
-                throw new Error("While scanning a " ~ name, startMark, e.msg, mark);
             }
             catch(UTFException e)
             {