Improve Zig AST developer experience

- Convert string-based type discrimination to type-safe enums
  - ContainerKind (struct, enum, union, opaque)
  - LiteralKind (int, float, string, char)
  - LoopKind (for, while)
- Remove duplicate AST nodes (consolidated init lists, removed unused types)
- Add comprehensive helper functions for all AST constructions
- Implement formatters for all AST nodes (expressions, statements, types)
- Add typed literal constructors: IntLit, FloatLit, StringLit, CharLit
- Improve documentation and add deprecation notices

This makes the AST more intuitive and type-safe for developers.

internal/zig/zig.go

@@ -119,6 +119,14 @@ func writeDecl(f *formatter, decl Decl) {
 		}
 		writeBlock(f, d.Block)
 		f.writef("\n")
+	case *UsingNamespaceDecl:
+		f.writef("usingnamespace ")
+		writeExpr(f, d.Expr)
+		f.writef(";\n")
+	case *ComptimeDecl:
+		f.writef("comptime")
+		writeBlock(f, d.Block)
+		f.writef("\n")
 	}
 }
 
@@ -148,6 +156,9 @@ func writeTypeExpr(f *formatter, typ TypeExpr) {
 		writeExpr(f, t.Size)
 		f.writef("]")
 		writeTypeExpr(f, t.Elem)
+	case *SliceTypeExpr:
+		f.writef("[]")
+		writeTypeExpr(f, t.Elem)
 	case *ErrorUnionTypeExpr:
 		writeTypeExpr(f, t.ErrSet)
 		f.writef("!")
@@ -217,7 +228,7 @@ func writeStmt(f *formatter, stmt Stmt) {
 		f.writef("if (")
 		writeExpr(f, s.Cond)
 		f.writef(")")
-		
+
 		// Handle payload if present
 		if s.Payload != nil {
 			f.writef(" ")
@@ -241,7 +252,7 @@ func writeStmt(f *formatter, stmt Stmt) {
 			}
 		}
 	case *LoopStmt:
-		if s.Kind == "while" {
+		if s.Kind == LoopWhile {
 			f.writef("while (")
 			if wp, ok := s.Prefix.(*WhilePrefix); ok {
 				writeExpr(f, wp.Cond)
@@ -258,7 +269,7 @@ func writeStmt(f *formatter, stmt Stmt) {
 				f.writef(" ")
 				writeStmt(f, s.Body)
 			}
-		} else if s.Kind == "for" {
+		} else if s.Kind == LoopFor {
 			f.writef("for (")
 			if fp, ok := s.Prefix.(*ForPrefix); ok {
 				for i, arg := range fp.Args {
@@ -289,45 +300,45 @@ func writeStmt(f *formatter, stmt Stmt) {
 				writeStmt(f, s.Body)
 			}
 		}
-		case *DeferStmt:
-			if s.ErrDefer {
-				f.writef("errdefer")
-			} else {
-				f.writef("defer")
-			}
-			f.writef(" ")
-			writeStmt(f, s.Stmt)
-		case *BreakStmt:
-			f.writef("break")
-			if s.Label != "" {
-				f.writef(" :%s", s.Label)
-			}
-			if s.Value != nil {
-				f.writef(" ")
-				writeExpr(f, s.Value)
-			}
-			f.writef(";")
-		case *ContinueStmt:
-			f.writef("continue")
-			if s.Label != "" {
-				f.writef(" :%s", s.Label)
-			}
-			f.writef(";")
-		case *SwitchStmt:
-			f.writef("switch (")
-			writeExpr(f, s.Cond)
-			f.writef(") {\n")
-			f.indent++
-			for _, prong := range s.Prongs {
-				f.writeIndent()
-				writeSwitchProng(f, prong)
-				f.writef("\n")
-			}
-			f.indent--
-			f.writeIndent()
-			f.writef("}")
+	case *DeferStmt:
+		if s.ErrDefer {
+			f.writef("errdefer")
+		} else {
+			f.writef("defer")
 		}
+		f.writef(" ")
+		writeStmt(f, s.Stmt)
+	case *BreakStmt:
+		f.writef("break")
+		if s.Label != "" {
+			f.writef(" :%s", s.Label)
+		}
+		if s.Value != nil {
+			f.writef(" ")
+			writeExpr(f, s.Value)
+		}
+		f.writef(";")
+	case *ContinueStmt:
+		f.writef("continue")
+		if s.Label != "" {
+			f.writef(" :%s", s.Label)
+		}
+		f.writef(";")
+	case *SwitchStmt:
+		f.writef("switch (")
+		writeExpr(f, s.Cond)
+		f.writef(") {\n")
+		f.indent++
+		for _, prong := range s.Prongs {
+			f.writeIndent()
+			writeSwitchProng(f, prong)
+			f.writef("\n")
+		}
+		f.indent--
+		f.writeIndent()
+		f.writef("}")
 	}
+}
 
 // writePayload emits a payload (|x|, |*x|, |*x, y|, etc).
 func writePayload(f *formatter, payload *Payload) {
@@ -431,7 +442,7 @@ func writeExpr(f *formatter, expr Expr) {
 		f.writef(".%s", e.Field)
 	case *Literal:
 		switch e.Kind {
-		case "string":
+		case LiteralString:
 			f.writef(`"%v"`, e.Value)
 		default:
 			f.writef("%v", e.Value)
@@ -456,11 +467,21 @@ func writeExpr(f *formatter, expr Expr) {
 			}
 		}
 	case *ContainerDecl:
-		if e.Kind == "struct" {
+		switch e.Kind {
+		case ContainerStruct:
 			f.writef("struct ")
 			writeStructBody(f, e)
-		} else {
-			panic("not implemented: " + e.Kind)
+		case ContainerEnum:
+			f.writef("enum ")
+			writeStructBody(f, e)
+		case ContainerUnion:
+			f.writef("union ")
+			writeStructBody(f, e)
+		case ContainerOpaque:
+			f.writef("opaque ")
+			writeStructBody(f, e)
+		default:
+			panic("unknown container kind")
 		}
 	case *TryExpr:
 		f.writef("try ")
@@ -489,6 +510,58 @@ func writeExpr(f *formatter, expr Expr) {
 		f.indent--
 		f.writeIndent()
 		f.writef("}")
+	case *GroupedExpr:
+		f.writef("(")
+		writeExpr(f, e.Expr)
+		f.writef(")")
+	case *ComptimeExpr:
+		f.writef("comptime ")
+		writeExpr(f, e.Expr)
+	case *NosuspendExpr:
+		f.writef("nosuspend ")
+		writeExpr(f, e.Expr)
+	case *AsyncExpr:
+		f.writef("async ")
+		writeExpr(f, e.Expr)
+	case *AwaitExpr:
+		f.writef("await ")
+		writeExpr(f, e.Expr)
+	case *ResumeExpr:
+		f.writef("resume ")
+		writeExpr(f, e.Expr)
+	case *DotAsteriskExpr:
+		writeExpr(f, e.Receiver)
+		f.writef(".*")
+	case *DotQuestionExpr:
+		writeExpr(f, e.Receiver)
+		f.writef(".?")
+	case *IfExpr:
+		f.writef("if (")
+		writeExpr(f, e.Cond)
+		f.writef(")")
+		if e.Payload != nil {
+			f.writef(" ")
+			writePayload(f, e.Payload)
+		}
+		f.writef(" ")
+		writeExpr(f, e.Then)
+		if e.Else != nil {
+			f.writef(" else ")
+			writeExpr(f, e.Else)
+		}
+	case *SwitchExpr:
+		f.writef("switch (")
+		writeExpr(f, e.Cond)
+		f.writef(") {\n")
+		f.indent++
+		for _, prong := range e.Prongs {
+			f.writeIndent()
+			writeSwitchProng(f, prong)
+			f.writef("\n")
+		}
+		f.indent--
+		f.writeIndent()
+		f.writef("}")
 	}
 }