Add if statements to templating engine

src/template/lib.zig

@@ -8,11 +8,13 @@ pub fn main() !void {
             &.{ "5", "4", "3", "2", "1" },
             &.{ "5", "4", "3", "2", "1" },
         },
+        .qux = true,
+        .quxx = false,
     });
 }
 
 pub fn execute(writer: anytype, comptime template: []const u8, args: anytype) !void {
-    @setEvalBranchQuota(@intCast(u32, template.len * 6));
+    @setEvalBranchQuota(@intCast(u32, template.len * 8));
     const tmpl = comptime parseTemplate(TokenIter{ .text = template }, .root);
     try executeTemplate(writer, tmpl.item, args, .{});
 }
@@ -42,6 +44,11 @@ fn executeStatement(writer: anytype, comptime stmt: Statement, args: anytype, ca
                 );
             }
         },
+        .if_statement => |if_stmt| {
+            const condition = evaluateExpression(if_stmt.condition, args, captures);
+            const subtemplate = if_stmt.subtemplate;
+            if (condition) try executeTemplate(writer, subtemplate, args, captures);
+        },
         else => @compileError("TODO"),
     }
 }
@@ -112,7 +119,8 @@ fn addCapture(root: anytype, comptime name: []const u8, val: anytype) AddCapture
 
 const TemplateType = enum {
     root,
-    subtemplate,
+    for_block,
+    if_block,
 };
 
 fn parseTemplate(comptime tokens: TokenIter, comptime template_type: TemplateType) ParseResult([]const TemplateItem) {
@@ -137,7 +145,9 @@ fn parseTemplate(comptime tokens: TokenIter, comptime template_type: TemplateTyp
                         const result = parseExpressionOrStatement(iter, true);
                         iter = result.new_iter;
                         if (result.item == .end_for) {
-                            if (template_type == .subtemplate) break :parse_loop else @compileError("Unexpected end statement");
+                            if (template_type == .for_block) break :parse_loop else @compileError("Unexpected end statement");
+                        } else if (result.item == .end_if) {
+                            if (template_type == .if_block) break :parse_loop else @compileError("Unexpected end statement");
                         }
                         items = items ++ [_]TemplateItem{.{ .statement = result.item }};
                     }
@@ -189,6 +199,13 @@ fn parseExpressionOrStatement(
                             .item = .{ .for_loop = result.item },
                         };
                     },
+                    .@"if" => {
+                        const result = parseIfStatement(iter);
+                        return .{
+                            .new_iter = result.new_iter,
+                            .item = .{ .if_statement = result.item },
+                        };
+                    },
 
                     //else => @compileError("TODO"),
                 }
@@ -202,6 +219,7 @@ fn parseExpressionOrStatement(
 
                 switch (keyword) {
                     .@"for" => break .{ .end_for = {} },
+                    .@"if" => break .{ .end_if = {} },
                 }
             },
             .period => {
@@ -283,9 +301,24 @@ fn parseForLoop(comptime tokens: TokenIter) ParseResult(ForLoop) {
         }
         iter = endStatement(iter);
 
-        const subtemplate = parseTemplate(iter, .subtemplate);
+        const subtemplate = parseTemplate(iter, .for_block);
 
-        return .{ .new_iter = subtemplate.new_iter, .item = .{ .iterable = iterable.item, .subtemplate = subtemplate.item, .capture = capture } };
+        return .{ .new_iter = subtemplate.new_iter, .item = .{
+            .iterable = iterable.item,
+            .subtemplate = subtemplate.item,
+            .capture = capture,
+        } };
+    }
+}
+
+fn parseIfStatement(comptime tokens: TokenIter) ParseResult(IfStatement) {
+    comptime {
+        const condition = parseExpressionOrStatement(tokens, false);
+        var iter = endStatement(condition.new_iter);
+
+        const subtemplate = parseTemplate(iter, .if_block);
+
+        return .{ .new_iter = subtemplate.new_iter, .item = .{ .condition = condition.item, .subtemplate = subtemplate.item } };
     }
 }
 
@@ -339,18 +372,27 @@ const ForLoop = struct {
     capture: []const u8,
 };
 
+const IfStatement = struct {
+    subtemplate: []const TemplateItem,
+    condition: Expression,
+};
+
 const Statement = union(enum) {
     expression: Expression,
     for_loop: ForLoop,
     end_for: void,
+    if_statement: IfStatement,
+    end_if: void,
 };
 
 const Keyword = enum {
     @"for",
+    @"if",
 };
 
 const EndKeyword = enum {
     @"for",
+    @"if",
 };
 
 const Token = union(enum) {

src/template/test.tmp.html

@@ -11,6 +11,8 @@
     <section>
       {#for .baz |$f|}{#for $f |$b|}{$b}:{/for}
       {/for}
+      {#if .qux}qux!{/if}
+      {#if .quxx}quxx!{/if}
     </section>
   </body>
 </html>