Add error for case/when on same line in ERB tag

config.yml

@@ -178,6 +178,13 @@ errors:
 
       fields: []
 
+    - name: ERBCaseWithConditionsError
+      message:
+        template: "A `case` statement with `when`/`in` in a single ERB tag cannot be formatted. Use separate tags for `case` and its conditions."
+        arguments: []
+
+      fields: []
+
 warnings:
   fields: []
   types: []

src/analyze.c

@@ -72,6 +72,14 @@ static bool analyze_erb_content(const AST_NODE_T* node, void* data) {
           erb_content_node->base.errors
         );
       }
+
+      if (analyzed->inline_conditionals_count > 0) {
+        append_erb_case_with_conditions_error(
+          erb_content_node->base.location.start,
+          erb_content_node->base.location.end,
+          erb_content_node->base.errors
+        );
+      }
     } else {
       erb_content_node->parsed = false;
       erb_content_node->valid = true;

src/analyze_helpers.c

@@ -406,6 +406,9 @@ bool search_unclosed_control_flows(const pm_node_t* node, void* data) {
 
       if (has_location(case_node->case_keyword_loc) && !is_end_keyword(case_node->end_keyword_loc)) {
         analyzed->unclosed_control_flow_count++;
+        if (case_node->conditions.size > 0) {
+          analyzed->inline_conditionals_count++;
+        }
       }
 
       break;
@@ -416,6 +419,13 @@ bool search_unclosed_control_flows(const pm_node_t* node, void* data) {
 
       if (has_location(case_match_node->case_keyword_loc) && !is_end_keyword(case_match_node->end_keyword_loc)) {
         analyzed->unclosed_control_flow_count++;
+        if (case_match_node->conditions.size > 0) {
+          analyzed->inline_conditionals_count++;
+        }
+
+        if (case_match_node->predicate && case_match_node->predicate->type == PM_MATCH_PREDICATE_NODE) {
+          analyzed->inline_conditionals_count++;
+        }
       }
 
       break;

src/analyzed_ruby.c

@@ -22,6 +22,7 @@ analyzed_ruby_T* init_analyzed_ruby(hb_string_T source) {
   analyzed->case_match_node_count = 0;
   analyzed->when_node_count = 0;
   analyzed->in_node_count = 0;
+  analyzed->inline_conditionals_count = 0;
   analyzed->for_node_count = 0;
   analyzed->while_node_count = 0;
   analyzed->until_node_count = 0;

src/include/analyzed_ruby.h

@@ -21,6 +21,7 @@ typedef struct ANALYZED_RUBY_STRUCT {
   int case_match_node_count;
   int when_node_count;
   int in_node_count;
+  int inline_conditionals_count;
   int for_node_count;
   int while_node_count;
   int until_node_count;

test/parser/multiple_control_flow_test.rb

@@ -361,5 +361,25 @@ class MultipleControlFlowTest < Minitest::Spec
         %>
       ERB
     end
+
+    test "case and when in same ERB tag" do
+      assert_parsed_snapshot(<<~ERB)
+        <% case variable when "a" %>
+          A
+        <% when "b" %>
+          B
+        <% end %>
+      ERB
+    end
+
+    test "case in pattern in same ERB tag" do
+      assert_parsed_snapshot(<<~ERB)
+        <% case value in 1 %>
+          One
+        <% in 2 %>
+          Two
+        <% end %>
+      ERB
+    end
   end
 end