[Bug #17398] Allow private def hello = puts "Hello"

This was a limitation of parse.y that prism intentionally replicated.

Author: Earlopain

snapshots/endless_methods_command_call.txt

@@ -19585,13 +19585,13 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, b
                 pm_do_loop_stack_push(parser, false);
                 statements = (pm_node_t *) pm_statements_node_create(parser);
 
-                // In endless method bodies, we need to handle command calls carefully.
-                // We want to allow command calls in assignment context but maintain
-                // the same binding power to avoid changing how operators are parsed.
-                // Note that we're intentionally NOT allowing code like `private def foo = puts "Hello"`
-                // because the original parser, parse.y, can't handle it and we want to maintain the same behavior
-                bool allow_command_call = (binding_power == PM_BINDING_POWER_ASSIGNMENT) ||
-                                         (binding_power < PM_BINDING_POWER_COMPOSITION);
+                bool allow_command_call;
+                if (parser->version >= PM_OPTIONS_VERSION_CRUBY_3_5) {
+                    allow_command_call = accepts_command_call;
+                } else {
+                    // Allow `def foo = puts "Hello"` but not `private def foo = puts "Hello"`
+                    allow_command_call = binding_power == PM_BINDING_POWER_ASSIGNMENT || binding_power < PM_BINDING_POWER_COMPOSITION;
+                }
 
                 pm_node_t *statement = parse_expression(parser, PM_BINDING_POWER_DEFINED + 1, allow_command_call, false, PM_ERR_DEF_ENDLESS, (uint16_t) (depth + 1));
 

src/prism.c

@@ -0,0 +1,3 @@
+private :m, def hello = puts "Hello"
+                             ^ unexpected string literal, expecting end-of-input
+

test/prism/errors/endless_method_command_call.txt

@@ -100,6 +100,15 @@ def foo(bar: bar) = 42
       end
     end
 
+    def test_private_endless_method
+      source = <<~RUBY
+        private def foo = puts "Hello"
+      RUBY
+
+      assert_predicate Prism.parse(source, version: "3.4"), :failure?
+      assert_predicate Prism.parse(source), :success?
+    end
+
     private
 
     def assert_errors(filepath)

test/prism/errors/private_endless_method.txt

@@ -0,0 +1,8 @@
+private def foo = puts "Hello"
+private def foo = puts "Hello", "World"
+private def foo = puts "Hello" do expr end
+private def foo() = puts "Hello"
+private def foo(x) = puts x
+private def obj.foo = puts "Hello"
+private def obj.foo() = puts "Hello"
+private def obj.foo(x) = puts x

test/prism/errors_test.rb

@@ -8,7 +8,6 @@ module Prism
   class FixturesTest < TestCase
     except = []
 
-
     if RUBY_VERSION < "3.3.0"
       # Ruby < 3.3.0 cannot parse heredocs where there are leading whitespace
       # characters in the heredoc start.
@@ -25,7 +24,9 @@ class FixturesTest < TestCase
       except << "whitequark/ruby_bug_19281.txt"
     end
 
-    except << "leading_logical.txt" if RUBY_VERSION < "3.5.0"
+    # Leaving these out until they are supported by parse.y.
+    except << "leading_logical.txt"
+    except << "endless_methods_command_call.txt"
 
     Fixture.each(except: except) do |fixture|
       define_method(fixture.test_name) { assert_valid_syntax(fixture.read) }

test/prism/fixtures/endless_methods_command_call.txt

@@ -45,6 +45,9 @@ class LexTest < TestCase
     # https://bugs.ruby-lang.org/issues/20925
     except << "leading_logical.txt"
 
+    # https://bugs.ruby-lang.org/issues/17398#note-12
+    except << "endless_methods_command_call.txt"
+
     Fixture.each(except: except) do |fixture|
       define_method(fixture.test_name) { assert_lex(fixture) }
     end

test/prism/fixtures_test.rb

@@ -29,7 +29,11 @@ class LocalsTest < TestCase
     except = [
       # Skip this fixture because it has a different number of locals because
       # CRuby is eliminating dead code.
-      "whitequark/ruby_bug_10653.txt"
+      "whitequark/ruby_bug_10653.txt",
+
+      # Leaving these out until they are supported by parse.y.
+      "leading_logical.txt",
+      "endless_methods_command_call.txt"
     ]
 
     Fixture.each(except: except) do |fixture|

test/prism/lex_test.rb

@@ -67,6 +67,9 @@ class ParserTest < TestCase
 
       # Cannot yet handling leading logical operators.
       "leading_logical.txt",
+
+      # Ruby >= 3.5 specific syntax
+      "endless_methods_command_call.txt",
     ]
 
     # These files contain code that is being parsed incorrectly by the parser