Add new -U command line option

This undefines a preprocessor symbol.

See #2591

CHANGES.current

@@ -7,6 +7,10 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.2.0 (in progress)
 ===========================
 
+2023-05-18: olly
+	    #2591 Add new -U command line option to undefine a preprocessor
+	    symbol.
+
 2023-05-18: olly
 	    #1589 #2335 Support parsing arbitrary expression in decltype.
 

Doc/Manual/SWIG.html

@@ -214,6 +214,7 @@ General Options
      -small          - Compile in virtual elimination and compact mode
      -swiglib        - Report location of SWIG library and exit
      -templatereduce - Reduce all the typedefs in templates
+     -U<symbol>      - Undefine symbol <symbol>
      -v              - Run in verbose mode
      -version        - Display SWIG version number
      -Wall           - Remove all warning suppression, also implies -Wextra

Examples/test-suite/command_line_define.i

@@ -5,3 +5,19 @@
 #if FOO-0 != 1
 # error "-DFOO didn't set FOO to 1"
 #endif
+
+// Test handling of -D with a value specified
+
+#if BAR-0 != 123
+# error "-DBAR=123 didn't set BAR to 123"
+#endif
+
+// Test handling of -U
+
+#ifdef BAZ
+# error "-UBAZ didn't undefine BAZ"
+#endif
+
+#ifdef NOTSET
+# error "-UNOTSET resulted in NOTSET getting set!"
+#endif

Examples/test-suite/common.mk

@@ -832,7 +832,7 @@ MULTI_CPP_TEST_CASES += \
 # Custom tests - tests with additional commandline options
 wallkw.cpptest: SWIGOPT += -Wallkw
 preproc_include.ctest: SWIGOPT += -includeall
-command_line_define.ctest: SWIGOPT += -DFOO
+command_line_define.ctest: SWIGOPT += -DFOO -DBAR=123 -DBAZ -UBAZ -UNOTSET
 
 # Allow modules to define temporarily failing tests.
 C_TEST_CASES := $(filter-out $(FAILING_C_TESTS),$(C_TEST_CASES))

Source/Modules/main.cxx

@@ -146,6 +146,7 @@ static const char *usage4 = (const char *) "\
      -small          - Compile in virtual elimination and compact mode\n\
      -swiglib        - Report location of SWIG library and exit\n\
      -templatereduce - Reduce all the typedefs in templates\n\
+     -U<symbol>      - Undefine symbol <symbol>\n\
      -v              - Run in verbose mode\n\
      -version        - Display SWIG version number\n\
      -Wall           - Remove all warning suppression, also implies -Wextra\n\
@@ -487,6 +488,9 @@ static void getoptions(int argc, char *argv[]) {
 	Preprocessor_define(d, 0);
 	Delete(d);
 	Swig_mark_arg(i);
+      } else if (strncmp(argv[i], "-U", 2) == 0) {
+	Preprocessor_undef(argv[i] + 2);
+	Swig_mark_arg(i);
       } else if (strcmp(argv[i], "-E") == 0) {
 	cpp_only = 1;
 	Swig_mark_arg(i);