From 8b98e660b1adf8e1b7d086a7823b11d58910b06e Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Tue, 21 May 2024 15:46:11 +0200
Subject: [PATCH 1/2] Fix block partial rendering

---
 askama_derive/src/generator.rs   |  5 +++++
 testing/tests/block_fragments.rs | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/askama_derive/src/generator.rs b/askama_derive/src/generator.rs
index decb01cb..32a81284 100644
--- a/askama_derive/src/generator.rs
+++ b/askama_derive/src/generator.rs
@@ -90,6 +90,7 @@ impl<'a> Generator<'a> {
         buf.write(CRATE);
         buf.writeln("::Result<()> {")?;
 
+        buf.discard = self.buf_writable.discard;
         // Make sure the compiler understands that the generated code depends on the template files.
         for path in self.contexts.keys() {
             // Skip the fake path of templates defined in rust source.
@@ -113,6 +114,7 @@ impl<'a> Generator<'a> {
         } else {
             self.handle(ctx, ctx.nodes, buf, AstLevel::Top)
         }?;
+        buf.discard = false;
 
         self.flush_ws(Ws(None, None));
         buf.write(CRATE);
@@ -987,6 +989,9 @@ impl<'a> Generator<'a> {
         if block_fragment_write {
             self.buf_writable.discard = true;
         }
+        if buf.discard != prev_buf_discard {
+            self.write_buf_writable(buf)?;
+        }
         buf.discard = prev_buf_discard;
 
         Ok(size_hint)
diff --git a/testing/tests/block_fragments.rs b/testing/tests/block_fragments.rs
index ae723b6d..502367db 100644
--- a/testing/tests/block_fragments.rs
+++ b/testing/tests/block_fragments.rs
@@ -103,3 +103,21 @@ fn test_specific_block() {
     let t = RenderInPlace { s1 };
     assert_eq!(t.render().unwrap(), "\nSection: [abc]\n");
 }
+
+#[derive(Template)]
+#[template(
+    source = r#"{% block empty %}
+{% endblock %}
+
+{% if let Some(var) = var %}
+{{ var }}
+{% endif %}"#,
+    block = "empty",
+    ext = "txt"
+)]
+struct Empty {}
+
+#[test]
+fn test_render_only_block() {
+    assert_eq!(Empty {}.render().unwrap(), "\n");
+}

From e44b0ca78d773e2c50cb2e5e7807a212f2633752 Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Thu, 23 May 2024 14:37:54 +0200
Subject: [PATCH 2/2] Add code comment to explain discard condition

---
 askama_derive/src/generator.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/askama_derive/src/generator.rs b/askama_derive/src/generator.rs
index 32a81284..9a8eb94f 100644
--- a/askama_derive/src/generator.rs
+++ b/askama_derive/src/generator.rs
@@ -989,6 +989,10 @@ impl<'a> Generator<'a> {
         if block_fragment_write {
             self.buf_writable.discard = true;
         }
+        // If we are rendering a specific block and the discard changed, it means that we're done
+        // with the block we want to render and that from this point, everything will be discarded.
+        //
+        // To get this block content rendered as well, we need to write to the buffer before then.
         if buf.discard != prev_buf_discard {
             self.write_buf_writable(buf)?;
         }