Fix C# regression in preprocessor directive parsing (#514)

* Fix C# regression in preprocessor directive parsing
It was due to a left-over syntax extension workaround that no longer
applies and was causing conflicts.

* Fix parsing of typed metavariables
Test 'Typed metavariable 3' was failing and was being parsed as binary
'<' and '>' operations.

Author: mjambon

lang/c-sharp-pro/test/ok/preproc_stmts.cs

@@ -0,0 +1,7 @@
+void F()
+{
+#if DEBUG
+    a();
+    b();
+#endif
+}

lang/semgrep-grammars/src/semgrep-c-sharp-pro/grammar.js

@@ -17,8 +17,6 @@ module.exports = grammar(standard_grammar, {
   conflicts: ($, previous) => [
     ...previous,
     [$.expression, $.parameter],
-    [$.file_scoped_namespace_declaration, $.preproc_if_in_top_level],
-    [$.file_scoped_namespace_declaration, $.preproc_else_in_top_level],
   ],
 
   rules: {
@@ -77,20 +75,6 @@ module.exports = grammar(standard_grammar, {
       )
     },
 
-    // We do this because a file scoped namespace declaration is a top-level 
-    // thing, but ellipses are more particular. We want ellipses to be used 
-    // in conjunction with file scoped namespace declarations.
-    // Unfortunately, in the base grammar, we can either have ellipsis 
-    // statements, or a file scoped declaration! That's no good. To play 
-    // around the previous grammar, we simply allow what came before to also 
-    // occur before a file scoped namespace declaration.
-    file_scoped_namespace_declaration: ($, previous) => {
-      return seq(
-        seq(repeat($.global_statement), repeat($._namespace_member_declaration)),
-        previous,
-      )
-    },
-
     enum_member_declaration: ($, previous) => choice(
           previous,
 	  $.ellipsis,
@@ -129,12 +113,12 @@ module.exports = grammar(standard_grammar, {
 
     // use syntax similar to a cast_expression, but with metavar
     //TODO: use PREC.CAST from original grammar instead of 17 below
-    typed_metavariable: $ => prec.right(17, seq(
+    typed_metavariable: $ => prec(17, prec.dynamic(1, seq(
       '(',
       field('type', $.type),
       field('metavar', $._semgrep_metavariable),
       ')',
-    )),
+    ))),
 
     deep_ellipsis: $ => seq(
       '<...', $.expression, '...>'

lang/semgrep-grammars/src/semgrep-c-sharp-pro/test/corpus/semgrep.txt

@@ -260,6 +260,52 @@ __SEMGREP_EXPRESSION
         (identifier))
       (argument_list))))
 
+===============================================================================
+Typed metavariable 2
+===============================================================================
+
+__SEMGREP_EXPRESSION (T $X)
+
+---
+
+(compilation_unit
+  (semgrep_expression
+    (typed_metavariable
+      (identifier))))
+
+===============================================================================
+Typed metavariable 3
+===============================================================================
+
+__SEMGREP_EXPRESSION (List<T> $X)
+
+---
+
+(compilation_unit
+  (semgrep_expression
+    (typed_metavariable
+      (generic_name
+        (identifier)
+        (type_argument_list
+          (identifier))))))
+
+===============================================================================
+Cast expression
+===============================================================================
+
+__SEMGREP_EXPRESSION (List<T>) x
+
+---
+
+(compilation_unit
+  (semgrep_expression
+    (cast_expression
+      (generic_name
+        (identifier)
+        (type_argument_list
+          (identifier)))
+      (identifier))))
+
 ================================================================================
 Ellipses + metavariables as args
 ================================================================================
@@ -376,3 +422,63 @@ namespace $N;
   (global_statement
     (expression_statement
       (ellipsis))))
+
+================================================================================
+Preprocessor conditional with single statement
+================================================================================
+
+void F()
+{
+#if DEBUG
+    a();
+#endif
+}
+
+---
+
+(compilation_unit
+  (global_statement
+    (local_function_statement
+      (predefined_type)
+      (identifier)
+      (parameter_list)
+      (block
+        (preproc_if
+          (identifier)
+          (expression_statement
+            (invocation_expression
+              (identifier)
+              (argument_list))))))))
+
+===============================================================================
+Preprocessor conditional with multiple statements
+===============================================================================
+
+void F()
+{
+#if DEBUG
+    a();
+    b();
+#endif
+}
+
+---
+
+(compilation_unit
+  (global_statement
+    (local_function_statement
+      (predefined_type)
+      (identifier)
+      (parameter_list)
+      (block
+        (preproc_if
+          (identifier)
+          (expression_statement
+            (invocation_expression
+              (identifier)
+              (argument_list)))
+          (expression_statement
+            (invocation_expression
+              (identifier)
+              (argument_list))))))))
+

lang/semgrep-grammars/src/semgrep-c-sharp/test/corpus/semgrep.txt

@@ -267,6 +267,35 @@ __SEMGREP_EXPRESSION
         (identifier))
       (argument_list))))
 
+===============================================================================
+Typed metavariable 2
+===============================================================================
+
+__SEMGREP_EXPRESSION (T $X)
+
+---
+
+(compilation_unit
+  (semgrep_expression
+    (typed_metavariable
+      (identifier))))
+
+===============================================================================
+Typed metavariable 3
+===============================================================================
+
+__SEMGREP_EXPRESSION (List<T> $X)
+
+---
+
+(compilation_unit
+  (semgrep_expression
+    (typed_metavariable
+      (generic_name
+        (identifier)
+        (type_argument_list
+          (identifier))))))
+
 ================================================================================
 Ellipses + metavariables as args
 ================================================================================