(#64) Add implicit context

Closes #64

src/main/controllers.zig

@@ -227,7 +227,7 @@ pub const Response = struct {
         defer stream.close();
 
         const writer = stream.writer();
-        try @import("template").execute(writer, .{}, templ, data);
+        try @import("template").execute(writer, .{}, templ, data, .{});
 
         try stream.finish();
     }

src/template/lib.zig

@@ -3,7 +3,7 @@ const std = @import("std");
 pub fn main() !void {
     try execute(
         std.io.getStdOut().writer(),
-        .{ .test_tmpl = "{.x}" },
+        .{ .test_tmpl = "{.x} {@context_foo}" },
         @embedFile("./test.tmp.html"),
         .{
             .community = .{ .name = "abcd" },
@@ -16,34 +16,57 @@ pub fn main() !void {
             .qux = false,
             .quxx = true,
         },
+        .{
+            .context_foo = "foo",
+        },
     );
 }
 
-pub fn execute(writer: anytype, comptime other_templates: anytype, comptime template: []const u8, args: anytype) !void {
+pub fn execute(
+    writer: anytype,
+    comptime other_templates: anytype,
+    comptime template: []const u8,
+    args: anytype,
+    context: anytype,
+) !void {
     @setEvalBranchQuota(@intCast(u32, template.len * 8));
 
     const tokens = comptime parseTemplateTokens(ControlTokenIter{ .text = template });
     const tmpl = comptime parseTemplate(tokens, 0, .root);
-    try executeTemplate(writer, other_templates, tmpl.items, args, .{});
+    try executeTemplate(writer, other_templates, tmpl.items, args, .{}, context);
 }
 
-fn executeTemplate(writer: anytype, comptime templates: anytype, comptime items: []const TemplateItem, args: anytype, captures: anytype) !void {
+fn executeTemplate(
+    writer: anytype,
+    comptime templates: anytype,
+    comptime items: []const TemplateItem,
+    args: anytype,
+    captures: anytype,
+    context: anytype,
+) !void {
     inline for (items) |it| {
         switch (it) {
             .text => |text| try writer.writeAll(text),
-            .statement => |stmt| try executeStatement(writer, templates, stmt, args, captures),
+            .statement => |stmt| try executeStatement(writer, templates, stmt, args, captures, context),
         }
     }
 }
 
-fn executeStatement(writer: anytype, comptime templates: anytype, comptime stmt: Statement, args: anytype, captures: anytype) !void {
+fn executeStatement(
+    writer: anytype,
+    comptime templates: anytype,
+    comptime stmt: Statement,
+    args: anytype,
+    captures: anytype,
+    context: anytype,
+) !void {
     switch (stmt) {
         .expression => |expr| {
-            const val = evaluateExpression(expr, args, captures);
+            const val = evaluateExpression(expr, args, captures, context);
             try print(writer, val);
         },
         .@"for" => |loop| {
-            const iterable = evaluateExpression(loop.header.iterable, args, captures);
+            const iterable = evaluateExpression(loop.header.iterable, args, captures, context);
             const subtemplate = loop.subtemplate;
             //std.log.debug("{any}", .{subtemplate});
             for (iterable) |v| {
@@ -53,25 +76,31 @@ fn executeStatement(writer: anytype, comptime templates: anytype, comptime stmt:
                     subtemplate,
                     args,
                     addCapture(captures, loop.header.capture, v),
+                    context,
                 );
             }
         },
         .@"if" => |if_stmt| {
-            const condition = evaluateExpression(if_stmt.header.condition, args, captures);
+            const condition = evaluateExpression(if_stmt.header.condition, args, captures, context);
             const subtemplate = if_stmt.subtemplate;
             if (condition) {
-                try executeTemplate(writer, templates, subtemplate, args, captures);
+                try executeTemplate(writer, templates, subtemplate, args, captures, context);
             } else {
                 if (if_stmt.else_branch) |branch| switch (branch) {
-                    .@"else" => |subtmpl| try executeTemplate(writer, templates, subtmpl, args, captures),
+                    .@"else" => |subtmpl| try executeTemplate(writer, templates, subtmpl, args, captures, context),
-                    .elif => |elif| try executeStatement(writer, templates, .{ .@"if" = elif.* }, args, captures),
+                    .elif => |elif| try executeStatement(writer, templates, .{ .@"if" = elif.* }, args, captures, context),
                 };
             }
         },
         .call_template => |call| {
             const new_template = @field(templates, call.template_name);
-            try execute(writer, templates, new_template, evaluateExpression(call.args, args, captures));
+            try execute(
-            //std.log.debug("calling template {s} with arg {any}", .{ call.template_name, call.args });
+                writer,
+                templates,
+                new_template,
+                evaluateExpression(call.args, args, captures, context),
+                context,
+            );
         },
         //else => @compileError("TODO"),
     }
@@ -102,10 +131,16 @@ fn deref(arg: anytype, comptime names: []const []const u8) Deref(@TypeOf(arg), n
     return deref(@field(arg, names[0]), names[1..]);
 }
 
-fn EvaluateExpression(comptime expression: Expression, comptime Args: type, comptime Captures: type) type {
+fn EvaluateExpression(
+    comptime expression: Expression,
+    comptime Args: type,
+    comptime Captures: type,
+    comptime Context: type,
+) type {
     return switch (expression) {
         .arg_deref => |names| Deref(Args, names),
         .capture_deref => |names| Deref(Captures, names),
+        .context_deref => |names| Deref(Context, names),
     };
 }
 
@@ -113,10 +148,12 @@ fn evaluateExpression(
     comptime expression: Expression,
     args: anytype,
     captures: anytype,
-) EvaluateExpression(expression, @TypeOf(args), @TypeOf(captures)) {
+    context: anytype,
+) EvaluateExpression(expression, @TypeOf(args), @TypeOf(captures), @TypeOf(context)) {
     return switch (expression) {
         .arg_deref => |names| deref(args, names),
         .capture_deref => |names| deref(captures, names),
+        .context_deref => |names| deref(context, names),
     };
 }
 
@@ -263,11 +300,9 @@ fn parseTemplate(
                             break cb
                         else
                             @compileError("Unexpected #else tag"),
-                        .call_template => |call| {
+                        .call_template => |call| items = items ++ [_]TemplateItem{.{
-                            items = items ++ [_]TemplateItem{.{
+                            .statement = .{ .call_template = call },
-                                .statement = .{ .call_template = call },
+                        }},
-                            }};
-                        },
                     }
                 },
             }
@@ -323,6 +358,7 @@ fn parseTemplateTokens(comptime tokens: ControlTokenIter) []const TemplateToken
             .dollar => items = items ++ [_]TemplateToken{.{ .text = "$" }},
             .slash => items = items ++ [_]TemplateToken{.{ .text = "/" }},
             .equals => items = items ++ [_]TemplateToken{.{ .text = "=" }},
+            .at => items = items ++ [_]TemplateToken{.{ .text = "@" }},
         };
 
         return items;
@@ -345,6 +381,11 @@ fn parseExpression(comptime tokens: ControlTokenIter) ParseResult(ControlTokenIt
                 iter = names.new_iter;
                 break .{ .capture_deref = names.item };
             },
+            .at => {
+                const names = parseDeref(iter);
+                iter = names.new_iter;
+                break .{ .context_deref = names.item };
+            },
             else => @compileError("TODO"),
         };
 
@@ -414,7 +455,7 @@ fn parseControlBlock(comptime tokens: ControlTokenIter) ParseResult(ControlToken
                     .@"if" => break .{ .end_if = {} },
                 }
             },
-            .period, .dollar => {
+            .period, .dollar, .at => {
                 iter.putBack(token);
                 const expr = parseExpression(iter);
                 iter = expr.new_iter;
@@ -587,6 +628,7 @@ const TemplateItem = union(enum) {
 const Expression = union(enum) {
     arg_deref: []const []const u8,
     capture_deref: []const []const u8,
+    context_deref: []const []const u8,
 };
 
 const For = struct {
@@ -664,6 +706,7 @@ const ControlToken = union(enum) {
     dollar: void,
     slash: void,
     equals: void,
+    at: void,
 };
 
 const ControlTokenIter = struct {
@@ -693,6 +736,7 @@ const ControlTokenIter = struct {
             '$' => return .{ .dollar = {} },
             '/' => return .{ .slash = {} },
             '=' => return .{ .equals = {} },
+            '@' => return .{ .at = {} },
             ' ', '\t', '\n', '\r' => {
                 var idx: usize = 0;
                 while (idx < remaining.len and std.mem.indexOfScalar(u8, " \t\n\r", remaining[idx]) != null) : (idx += 1) {}
@@ -704,7 +748,7 @@ const ControlTokenIter = struct {
             },
             else => {
                 var idx: usize = 0;
-                while (idx < remaining.len and std.mem.indexOfScalar(u8, "{}.#|$/= \t\n\r", remaining[idx]) == null) : (idx += 1) {}
+                while (idx < remaining.len and std.mem.indexOfScalar(u8, "{}.#|$/=@ \t\n\r", remaining[idx]) == null) : (idx += 1) {}
 
                 self.start += idx - 1;
                 return .{ .text = remaining[0..idx] };
@@ -728,7 +772,7 @@ test "template" {
     const testCase = struct {
         fn case(comptime tmpl: []const u8, args: anytype, expected: []const u8) !void {
             var stream = std.io.changeDetectionStream(expected, std.io.null_writer);
-            try execute(stream.writer(), tmpl, args);
+            try execute(stream.writer(), .{}, tmpl, args, .{});
             try std.testing.expect(!stream.changeDetected());
         }
     }.case;

src/template/test.tmp.html

@@ -23,6 +23,8 @@
       {=/if}
 
       <template>{#template test_tmpl .bar}</template>
+
+      {@context_foo}
     </section>
   </body>
 </html>