supported istring as TemplateSingleArgument

Author: WebFreak001

src/dparse/ast.d

@@ -16,10 +16,10 @@
 module dparse.ast;
 
 import dparse.lexer;
-import std.traits;
 import std.algorithm;
 import std.array;
 import std.string;
+import std.traits;
 
 private immutable uint[TypeInfo] typeMap;
 
@@ -1425,8 +1425,8 @@ final class Declaration : BaseNode
         }
     }
 
-    private import std.variant:Algebraic;
-    private import std.typetuple:TypeTuple;
+    import std.typetuple : TypeTuple;
+    import std.variant : Algebraic;
 
     alias DeclarationTypes = TypeTuple!(AliasDeclaration, AliasAssign, AliasThisDeclaration,
         AnonymousEnumDeclaration, AttributeDeclaration,
@@ -3483,9 +3483,10 @@ final class TemplateSingleArgument : BaseNode
 {
     override void accept(ASTVisitor visitor) const
     {
-        mixin (visitIfNotNull!(token));
+        mixin (visitIfNotNull!(token, istring));
     }
     /** */ Token token;
+    /** */ InterpolatedString istring;
     mixin OpEquals;
 }
 
@@ -4092,7 +4093,7 @@ unittest //#365 : used to segfault
 unittest // issue #398: Support extern(C++, <string expressions...>)
 {
     import dparse.lexer : LexerConfig;
-    import dparse.parser : ParserConfig, parseModule;
+    import dparse.parser : parseModule, ParserConfig;
     import dparse.rollback_allocator : RollbackAllocator;
 
     RollbackAllocator ra;

src/dparse/formatter.d

@@ -3290,7 +3290,10 @@ class Formatter(Sink)
         **/
 
         put("!");
-        format(templateSingleArgument.token);
+        if (templateSingleArgument.istring)
+            format(templateSingleArgument.istring);
+        else
+            format(templateSingleArgument.token);
     }
 
     void format(const TemplateThisParameter templateThisParameter)
@@ -4405,5 +4408,10 @@ z /// Documentation for z
     testFormatNode!(VariableDeclaration)(`T x = i" hello $(name) ";`);
     testFormatNode!(VariableDeclaration)(`T x = i" hello $( name ) ";`, `T x = i" hello $(name) ";`);
     testFormatNode!(VariableDeclaration)(`auto a = iq{ "}" hi };`, `auto a = iq{ "}" hi };`);
-    testFormatNode!(VariableDeclaration)("T x = iq{\n};", "T x = iq{\n};");
+    testFormatNode!(VariableDeclaration)("T x = iq{\n};");
+    testFormatNode!(AliasDeclaration)(`alias expr = AliasSeq!i"$(a) $(b)";`);
+    testFormatNode!(VariableDeclaration)(q{auto thing = i"$(b) $("$" ~ ')' ~ `"`)";});
+    testFormatNode!(VariableDeclaration)("auto x = i` $(b) is $(b)!`;");
+    testFormatNode!(VariableDeclaration)("auto x = iq{ $(b) is $(b)!};");
+    testFormatNode!(VariableDeclaration)("auto x = iq{{$('$')}};");
 }

src/dparse/parser.d

@@ -7254,6 +7254,7 @@ class Parser
      *     | $(LITERAL StringLiteral)
      *     | $(LITERAL IntegerLiteral)
      *     | $(LITERAL FloatLiteral)
+     *     | $(LITERAL InterpolatedString)
      *     | $(LITERAL '_true')
      *     | $(LITERAL '_false')
      *     | $(LITERAL '_null')
@@ -7289,6 +7290,9 @@ class Parser
         foreach (C; BasicTypes) { case C: }
             node.token = advance();
             break;
+        case tok!"istringLiteralStart":
+            node.istring = parseInterpolatedString();
+            break;
         default:
             error(`Invalid template argument. (Try enclosing in parenthesis?)`);
             return null;