From 2a05c59b5f820bd7f4eeee0d84df86e6295b5643 Mon Sep 17 00:00:00 2001
From: Marc Worrell <marc@worrell.nl>
Date: Fri, 13 Dec 2024 16:04:03 +0100
Subject: [PATCH] Fix a problem where having duplicated blocks could result in
 endless recursion (#55)

---
 src/template_compiler.erl              | 45 +++++++++++++++++++++-----
 test/template_compiler_basic_SUITE.erl |  5 +++
 test/test-data/block_nested_error.tpl  |  9 ++++++
 3 files changed, 51 insertions(+), 8 deletions(-)
 create mode 100644 test/test-data/block_nested_error.tpl

diff --git a/src/template_compiler.erl b/src/template_compiler.erl
index 19e965b..40f65fa 100644
--- a/src/template_compiler.erl
+++ b/src/template_compiler.erl
@@ -423,18 +423,33 @@ cs(Module, Filename, Options, Context) ->
 
 compile_tokens({ok, {extends, {string_literal, _, Extend}, Elements}}, CState, _Options) ->
     Blocks = find_blocks(Elements),
-    {Ws, BlockAsts} = compile_blocks(Blocks, CState),
-    {ok, {Extend, Ws#ws.includes, BlockAsts, undefined, Ws#ws.is_autoid_var}};
+    case check_duplicate_blocks(Blocks) of
+        ok ->
+            {Ws, BlockAsts} = compile_blocks(Blocks, CState),
+            {ok, {Extend, Ws#ws.includes, BlockAsts, undefined, Ws#ws.is_autoid_var}};
+        {error, _} = Error ->
+            Error
+    end;
 compile_tokens({ok, {overrules, Elements}}, CState, _Options) ->
     Blocks = find_blocks(Elements),
-    {Ws, BlockAsts} = compile_blocks(Blocks, CState),
-    {ok, {overrules, Ws#ws.includes, BlockAsts, undefined, Ws#ws.is_autoid_var}};
+    case check_duplicate_blocks(Blocks) of
+        ok ->
+            {Ws, BlockAsts} = compile_blocks(Blocks, CState),
+            {ok, {overrules, Ws#ws.includes, BlockAsts, undefined, Ws#ws.is_autoid_var}};
+        {error, _} = Error ->
+            Error
+    end;
 compile_tokens({ok, {base, Elements}}, CState, _Options) ->
     Blocks = find_blocks(Elements),
-    {Ws, BlockAsts} = compile_blocks(Blocks, CState),
-    CStateElts = CState#cs{blocks = BlockAsts},
-    {Ws1, TemplateAsts} = template_compiler_element:compile(Elements, CStateElts, Ws),
-    {ok, {undefined, Ws1#ws.includes, BlockAsts, TemplateAsts, Ws1#ws.is_autoid_var}};
+    case check_duplicate_blocks(Blocks) of
+        ok ->
+            {Ws, BlockAsts} = compile_blocks(Blocks, CState),
+            CStateElts = CState#cs{blocks = BlockAsts},
+            {Ws1, TemplateAsts} = template_compiler_element:compile(Elements, CStateElts, Ws),
+            {ok, {undefined, Ws1#ws.includes, BlockAsts, TemplateAsts, Ws1#ws.is_autoid_var}};
+        {error, _} = Error ->
+            Error
+    end;
 compile_tokens({error, {Loc, template_compiler_parser, Msg}}, #cs{ filename = Filename }, Options) ->
     % Try format the Yecc error
     Err = split_loc(Loc),
@@ -522,6 +537,20 @@ block_elements({filter, _, Elts}) -> Elts;
 block_elements(_) -> [].
 
 
+check_duplicate_blocks(Blocks) ->
+    check_duplicate_blocks_1(Blocks, #{}).
+
+check_duplicate_blocks_1([], _Acc) ->
+    ok;
+check_duplicate_blocks_1([{block, {identifier, _Pos, Name}, _Elements}|Blocks], Acc) ->
+    case maps:is_key(Name, Acc) of
+        true ->
+            {error, {duplicate_block, Name}};
+        false ->
+            check_duplicate_blocks_1(Blocks, Acc#{ Name => true })
+    end.
+
+
 %% @doc Optionally drop text before {% extends %} or {% overrules %}.
 maybe_drop_text([{text, _SrcRef, _Text}|Rest], OrgTks) ->
     maybe_drop_text(Rest, OrgTks);
diff --git a/test/template_compiler_basic_SUITE.erl b/test/template_compiler_basic_SUITE.erl
index 2e87647..dd175c8 100644
--- a/test/template_compiler_basic_SUITE.erl
+++ b/test/template_compiler_basic_SUITE.erl
@@ -23,6 +23,7 @@ groups() ->
         ,hello_world_block2_test
         ,hello_world_block3_test
         ,hello_world_comment_test
+        ,block_nested_error_test
         ,block_render_test
         ,raw_test
         ]}].
@@ -72,6 +73,10 @@ hello_world_comment_test(_Config) ->
     <<"Hello World!">> = iolist_to_binary(Bin),
     ok.
 
+block_nested_error_test(_Config) ->
+    {error, {duplicate_block, <<"main">>}} = template_compiler:render("block_nested_error.tpl", #{}, [], undefined),
+    ok.
+
 block_render_test(_Config) ->
     {ok, BinA} = template_compiler:render_block(a, "block_render.tpl", #{}, [], undefined),
     <<"A">> = iolist_to_binary(BinA),
diff --git a/test/test-data/block_nested_error.tpl b/test/test-data/block_nested_error.tpl
new file mode 100644
index 0000000..54239eb
--- /dev/null
+++ b/test/test-data/block_nested_error.tpl
@@ -0,0 +1,9 @@
+{% block main %}
+    Hallo
+    {% block test %}
+        Daar
+        {% block main %}
+            oops - a block with the same name
+        {% endblock %}
+    {% endblock %}
+{% endblock%}