Improved if statement generation to avoid issues with implicit borrows (#392)

* Changed to automatically coerce to bool

* Added new test case

* Updated test case to include else if

3 files changed, 72 insertions, 0 deletions

diff --git a/askama_shared/src/generator.rs b/askama_shared/src/generator.rs
index 3a91e3c..ad086a3 100644
--- a/askama_shared/src/generator.rs
+++ b/askama_shared/src/generator.rs
@@ -518,8 +518,15 @@ impl<'a, S: std::hash::BuildHasher> Generator<'a, S> {
                         buf.dedent()?;
                         buf.write("} else if ");
                     }
+                    // The following syntax `*(&(...) as &bool)` is used to
+                    // trigger Rust's automatic dereferencing, to coerce
+                    // e.g. `&&&&&bool` to `bool`. First `&(...) as &bool`
+                    // coerces e.g. `&&&bool` to `&bool`. Then `*(&bool)`
+                    // finally dereferences it to `bool`.
+                    buf.write("*(&(");
                     let expr_code = self.visit_expr_root(expr)?;
                     buf.write(&expr_code);
+                    buf.write(") as &bool)");
                 }
                 None => {
                     buf.dedent()?;
diff --git a/testing/templates/if-coerce.html b/testing/templates/if-coerce.html
new file mode 100644
index 0000000..e32c2fe
--- /dev/null
+++ b/testing/templates/if-coerce.html
@@ -0,0 +1,51 @@
+{% macro foo(b) -%}
+    {% if b %}t{% else %}f{% endif -%}
+{% endmacro -%}
+
+{% macro bar(b) -%}
+    {%- call foo(b) -%}
+{% endmacro -%}
+
+{% macro baz(b) -%}
+    {%- call bar(b) -%}
+{% endmacro -%}
+
+{% macro qux(b) -%}
+    {%- call baz(b) -%}
+{% endmacro -%}
+
+{%- call foo(false) -%}
+{%- call bar(true) -%}
+{%- call baz(false) -%}
+{%- call qux(true) -%}
+
+{%- call qux(true && false) -%}
+{%- call qux(false || true) -%}
+
+{%- call qux(self.t) -%}
+{%- call qux(self.f) -%}
+{%- call qux(self.f || self.t) -%}
+
+{%- if false -%}
+if
+{%- else if false || true -%}
+elseif
+{%- else -%}
+else
+{%- endif -%}
+
+{%- if true && false -%}
+if
+{%- else if false -%}
+elseif
+{%- else -%}
+else
+{%- endif -%}
+
+{%- if false || true -%}
+if
+{%- else if (true && false) -%}
+elseif
+{%- else -%}
+else
+{%- endif -%}
diff --git a/testing/tests/coerce.rs b/testing/tests/coerce.rs
new file mode 100644
index 0000000..1a44781
--- /dev/null
+++ b/testing/tests/coerce.rs
@@ -0,0 +1,14 @@
+use askama::Template;
+
+#[derive(Template)]
+#[template(path = "if-coerce.html")]
+struct IfCoerceTemplate {
+    t: bool,
+    f: bool,
+}
+
+#[test]
+fn test_coerce() {
+    let t = IfCoerceTemplate { t: true, f: false };
+    assert_eq!(t.render().unwrap(), "ftftfttftelseifelseif");
+}