Diagnose an empty diag_suppress pragma without reading past it. [GH #203]

Author: mohitmishra786

src/Changes

@@ -20,6 +20,21 @@ C++-generating back end: inaccessible or out-of-scope template arguments
 In certain complex cases, the C++-generating back end could put out a
 template argument that uses an inaccessible or out-of-scope name, making
 the generated code uncompilable.  This is now fixed.
+10/6/26  [GH #203]
+Assertion failure on an empty diag_suppress pragma
+
+A diag_suppress (or similar) pragma with no arguments, or with a trailing
+comma, diagnosed the missing argument and then read past the end of the
+directive.  That, in turn, could lead to an assertion failure in
+process_immediate_pragmas.  For example:
+
+  #pragma diagnostic push
+  #pragma diag_suppress
+  int f() { int a; return a; }
+  #pragma diagnostic pop
+
+That is now fixed: The missing argument is still diagnosed, and the code after
+the pragma is parsed.
 
 
 10/5/26  [GH #213]

src/error.c

@@ -8176,8 +8176,11 @@ as _Pragma that are not parsed except during instantiations).
       err = TRUE;
       pos_warning(ec_exp_error_argument, &pos_curr_token);
     }  /* if */
-    /* Bypass the token just processed. */
-    (void)get_token();
+    /* Advance past the argument.  Do not consume tok_end_of_source here.
+       Fetching that terminator already popped the pragma token cache, so
+       another get_token would read the source that follows the pragma and
+       could queue later pragmas while this one is still being processed. */
+    if (curr_token != tok_end_of_source) (void)get_token();
     if (curr_token != tok_comma && curr_token != tok_end_of_source) {
       pos_warning(ec_exp_comma, &pos_curr_token);
       error_in_pragma = TRUE;

tests/tests/changes/.GH19.rto/default.1.1.txt

@@ -0,0 +1,33 @@
+fe_only -DTEST_NUMBER=1 Test_name.c
+"Test_name.c", line 9: warning: expected an error number or error tag
+  #pragma diag_suppress
+                       ^
+
+"Test_name.c", line 13: warning: variable "a" is used before its value is set
+    return a;
+           ^
+
+"Test_name.c", line 20: warning: variable "b" is used before its value is set
+    return b;
+           ^
+
+"Test_name.c", line 23: warning: expected an error number or error tag
+  #pragma diag_suppress =
+                         ^
+
+"Test_name.c", line 27: warning: variable "c" is used before its value is set
+    return c;
+           ^
+
+"Test_name.c", line 30: warning: expected an error number or error tag
+  #pragma diag_suppress 123,
+                            ^
+
+"Test_name.c", line 34: warning: variable "d" is used before its value is set
+    return d;
+           ^
+
+"Test_name.c", line 41: warning: variable "e" is used before its value is set
+    return e;
+           ^
+

tests/tests/changes/GH19.sft.cpp

@@ -0,0 +1,43 @@
+//type:fp
+//remark:[GH #19] Assertion failure on an empty diag_suppress pragma
+// 10/3/26  [GH #19]
+//
+// An empty #pragma diag_suppress used to read past the directive and assert
+// in process_immediate_pragmas.  The functions below must still be compiled.
+
+#pragma diagnostic push
+#pragma diag_suppress
+int get_free_no_warn()
+{
+  int a;
+  return a;
+}
+#pragma diagnostic pop
+
+int get_free_warn()
+{
+  int b;
+  return b;
+}
+
+#pragma diag_suppress =
+int after_bare_equals()
+{
+  int c;
+  return c;
+}
+
+#pragma diag_suppress 123,
+int after_trailing_comma()
+{
+  int d;
+  return d;
+}
+
+#pragma diag_suppress = 123
+int after_valid_pragma()
+{
+  int e;
+  return e;
+}
+#pragma diag_default 123