From 27ee0ecd5d415003c543d7f25cdbac707ffe91ab Mon Sep 17 00:00:00 2001
From: jaina heartles <me@heartles.xyz>
Date: Wed, 14 Dec 2022 02:57:27 -0800
Subject: [PATCH] Add support for array.len pseudo-field

---
 src/template/lib.zig | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/template/lib.zig b/src/template/lib.zig
index c5fb6b6..4e8803c 100644
--- a/src/template/lib.zig
+++ b/src/template/lib.zig
@@ -215,6 +215,17 @@ fn print(writer: anytype, arg: anytype) !void {
 
 const ExpressionError = error{ IndexOutOfBounds, NullOptional };
 
+fn Deref(comptime T: type, comptime field: []const u8) type {
+    if (std.meta.trait.isIndexable(T) and std.mem.eql(u8, field, "len")) return usize;
+    switch (@typeInfo(T)) {
+        .Pointer => return Deref(std.meta.Child(T), field),
+        .Struct => |info| for (info.fields) |f| {
+            if (std.mem.eql(u8, field, f.name)) return f.field_type;
+        } else @compileError("Field " ++ field ++ " does not exist on type " ++ @typeName(T)),
+        else => @compileError("Cannot retrieve field " ++ field ++ " from type " ++ @typeName(T)),
+    }
+}
+
 fn EvaluateExpression(
     comptime expression: Expression,
     comptime Args: type,
@@ -227,9 +238,7 @@ fn EvaluateExpression(
         .context => Context,
         .deref => |expr| {
             const T = EvaluateExpression(expr.container, Args, Captures, Context);
-            for (@typeInfo(T).Struct.fields) |f| {
-                if (std.mem.eql(u8, expr.field, f.name)) return f.field_type;
-            } else @compileError("Field " ++ expr.field ++ " does not exist on type " ++ @typeName(T));
+            return Deref(T, expr.field);
         },
         .equals => bool,
         .builtin => |call| switch (call.*) {
@@ -300,12 +309,14 @@ fn AddCapture(comptime Root: type, comptime name: []const u8, comptime Val: type
         .alignment = @alignOf(Val),
     }};
 
-    return @Type(.{ .Struct = .{
+    const Result = @Type(.{ .Struct = .{
         .layout = .Auto,
         .fields = fields,
         .decls = &.{},
         .is_tuple = false,
     } });
+
+    return Result;
 }
 
 fn addCapture(root: anytype, comptime name: []const u8, val: anytype) AddCapture(@TypeOf(root), name, @TypeOf(val)) {