compiler: -g and -debug should always add -g at least in the C compiler by default

* compiler: -g and -debug should always add -g at least in the C compiler by default.

* Set first the C backend debug_options, so that the optimization_options can override them later.

* Implement cleaner named is_debug, is_vlines, is_keep_c and is_cache options (i.e. -g/-cg, -keep_c, -cache v flags).

* Check and reset file/line numbers in the generated main program, only if v.pref.is_vlines is true.

compiler/cc.v

@@ -77,29 +77,30 @@ fn (v mut V) cc() {
 		println('Building ${v.out_name}...')
 	}
 
-	mut debug_options := ''
+	debug_mode := v.pref.is_debug
+	mut debug_options := '-g'
 	mut optimization_options := '-O2'
 	if v.pref.ccompiler.contains('clang') {
-		if v.pref.is_debuggable {
+		if debug_mode {
 			debug_options = '-g -O0'
 		}
 		optimization_options = '-O3 -flto'
 	}
 	if v.pref.ccompiler.contains('gcc') {
-		if v.pref.is_debug {
+		if debug_mode {
 			debug_options = '-g3'
 		}
 		optimization_options = '-O3 -fno-strict-aliasing -flto'
 	}
 	
+	if debug_mode {
+		a << debug_options
+	}
 	if v.pref.is_prod {
 		a << optimization_options
 	}
-	else {
-		a << debug_options
-	}
 	
-	if v.pref.is_debuggable && os.user_os() != 'windows'{
+	if debug_mode && os.user_os() != 'windows'{
 		a << ' -rdynamic ' // needed for nicer symbolic backtraces
 	}
 
@@ -115,7 +116,7 @@ fn (v mut V) cc() {
 	if v.pref.build_mode == .build_module {
 		a << '-c'
 	}
-	else if v.pref.is_debug {
+	else if v.pref.is_cache {
 		vexe := os.executable()
 		builtin_o_path := '$v_modules_path${os.PathSeparator}cache${os.PathSeparator}vlib${os.PathSeparator}builtin.o'
 		if os.file_exists(builtin_o_path) {
@@ -225,7 +226,7 @@ fn (v mut V) cc() {
 			partial_output := res.output.limit(200).trim_right('\r\n')
 			print(partial_output)
 			if res.output.len > partial_output.len {
-				println('...\n(Use `v -debug` to print the entire error message)\n')
+				println('...\n(Use `v -g` to print the entire error message)\n')
 			}else{
 				println('')
 			}
@@ -261,7 +262,7 @@ fn (v mut V) cc() {
 		println('linux cross compilation done. resulting binary: "$v.out_name"')
 	}
 	*/
-	if !v.pref.is_debug && v.out_name_c != 'v.c' {
+	if !v.pref.is_keep_c && v.out_name_c != 'v.c' {
 		os.rm(v.out_name_c)
 	}
 	if v.pref.compress {

compiler/fn.v

@@ -807,7 +807,7 @@ fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
 		p.check(.rpar)
 		return f
 	}
-	// add debug information to panic when -debug arg is passed
+	// add debug information to panic when -g arg is passed
 	if p.v.pref.is_debug && f.name == 'panic' && !p.is_js {
 		mod_name := p.mod.replace('_dot_', '.')
 		fn_name := p.cur_fn.name.replace('${p.mod}__', '')

compiler/live.v

@@ -82,13 +82,8 @@ fn (v &V) generate_hot_reload_code() {
 			msvc = '-os msvc'
 		}
 		
-		mut debug := ''
+		so_debug_flag := if v.pref.is_debug { '-g' } else { '' }		
-		
+		cmd_compile_shared_library := '$vexe $msvc $so_debug_flag -o $file_base -shared $file'
-		if v.pref.is_debug {
-			debug = '-debug'
-		}
-		
-		cmd_compile_shared_library := '$vexe $msvc $debug -o $file_base -shared $file'
 		if v.pref.show_c_cmd {
 			println(cmd_compile_shared_library)
 		}

compiler/main.v

@@ -91,8 +91,14 @@ mut:
 	is_run        bool
 	show_c_cmd    bool   // `v -show_c_cmd` prints the C command to build program.v.c
 	sanitize      bool   // use Clang's new "-fsanitize" option
-	is_debuggable bool
+	
-	is_debug      bool   // keep compiled C files
+	is_debug      bool   // false by default, turned on by -g or -cg, it tells v to pass -g to the C backend compiler.
+	is_vlines     bool   // turned on by -g, false by default (it slows down .tmp.c generation slightly).
+	is_keep_c     bool   // -keep_c , tell v to leave the generated .tmp.c alone (since by default v will delete them after c backend finishes)
+	// NB: passing -cg instead of -g will set is_vlines to false and is_g to true, thus making v generate cleaner C files,
+	// which are sometimes easier to debug / inspect manually than the .tmp.c files by plain -g (when/if v line number generation breaks).
+	is_cache      bool   // turns on v usage of the module cache to speed up compilation.
+	
 	is_stats      bool   // `v -stats file_test.v` will produce more detailed statistics for the tests that were run
 	no_auto_free  bool   // `v -nofree` disable automatic `free()` insertion for better performance in some applications  (e.g. compilers)
 	cflags        string // Additional options which will be passed to the C compiler.
@@ -460,6 +466,7 @@ fn (v mut V) generate_main() {
 	mut cgen := v.cgen
 	$if js { return }
 
+	if v.pref.is_vlines {
 		///// After this point, the v files are compiled.
 		///// The rest is auto generated code, which will not have
 		///// different .v source file/line numbers.
@@ -468,6 +475,7 @@ fn (v mut V) generate_main() {
 		cgen.genln('////////////////// Reset the file/line numbers //////////')
 		cgen.lines << '#line $lines_so_far "${cescaped_path(os.realpath(cgen.out_path))}"'
 		cgen.genln('')
+	}
 
 	// Make sure the main function exists
 	// Obviously we don't need it in libraries
@@ -612,7 +620,7 @@ fn (v mut V) add_v_files_to_compile() {
 	mut builtin_files := v.get_builtin_files()
 	// Builtin cache exists? Use it.
 	builtin_vh := '$v_modules_path${os.PathSeparator}vlib${os.PathSeparator}builtin.vh'
-	if v.pref.is_debug && os.file_exists(builtin_vh) {
+	if v.pref.is_cache && os.file_exists(builtin_vh) {
 		v.cached_mods << 'builtin'
 		builtin_files = [builtin_vh]
 	}
@@ -656,7 +664,7 @@ fn (v mut V) add_v_files_to_compile() {
 		if v.pref.build_mode != .build_module && !mod.contains('vweb') {
 			mod_path := mod.replace('.', os.PathSeparator)
 			vh_path := '$v_modules_path${os.PathSeparator}vlib${os.PathSeparator}${mod_path}.vh'
-			if v.pref.is_debug && os.file_exists(vh_path) {
+			if v.pref.is_cache && os.file_exists(vh_path) {
 				println('using cached module `$mod`: $vh_path')
 				v.cached_mods << mod
 				v.files << vh_path
@@ -941,8 +949,12 @@ fn new_v(args[]string) &V {
 		is_so: '-shared' in args
 		is_prod: '-prod' in args
 		is_verbose: '-verbose' in args || '--verbose' in args
-		is_debuggable: '-g' in args
+
-		is_debug: '-debug' in args || '-g' in args
+		is_debug:      '-g' in args || '-cg' in args
+		is_vlines:     '-g' in args && !('-cg' in args)
+		is_keep_c:     '-keep_c' in args
+		is_cache:      '-cache' in args
+				
 		is_stats: '-stats' in args
 		obfuscate: obfuscate
 		is_prof: '-prof' in args

compiler/msvc.v

@@ -213,7 +213,7 @@ fn find_msvc() ?MsvcResult {
 pub fn (v mut V) cc_msvc() {
 	r := find_msvc() or {
 		// TODO: code reuse
-		if !v.pref.is_debug && v.out_name_c != 'v.c' && v.out_name_c != 'v_macos.c' {
+		if !v.pref.is_keep_c && v.out_name_c != 'v.c' && v.out_name_c != 'v_macos.c' {
 			os.rm(v.out_name_c)
 		}
 		verror('Cannot find MSVC on this OS')
@@ -358,7 +358,7 @@ pub fn (v mut V) cc_msvc() {
 	// println(res)
 	// println('C OUTPUT:')
 
-	if !v.pref.is_debug && v.out_name_c != 'v.c' && v.out_name_c != 'v_macos.c' {
+	if !v.pref.is_keep_c && v.out_name_c != 'v.c' && v.out_name_c != 'v_macos.c' {
 		os.rm(v.out_name_c)
 	}
 

compiler/parser.v

@@ -103,7 +103,7 @@ fn (v mut V) new_parser_from_string(text string, id string) Parser {
 fn (v mut V) reset_cgen_file_line_parameters(){
 	v.cgen.line = 0
 	v.cgen.file = ''
-	v.cgen.line_directives = v.pref.is_debuggable
+	v.cgen.line_directives = v.pref.is_vlines
 }
 
 fn (v mut V) new_parser_from_file(path string) Parser {

compiler/vhelp.v

@@ -39,19 +39,28 @@ Options/commands:
   -os <OS>          Produce an executable for the selected OS.
                     OS can be linux, mac, windows, msvc.
                     Use msvc if you want to use the MSVC compiler on Windows.
+  -shared           Build a shared library.
+  -stats            Show additional stats when compiling/running tests. Try `v -stats test .`
+
+  -cache            Turn on usage of the precompiled module cache. 
+                    It very significantly speeds up secondary compilations.
+
+  -obf              Obfuscate the resulting binary.
+  -                 Shorthand for `v runrepl`.
+
+Options for debugging/troubleshooting v programs:
+  -g                Generate debugging information in the backtraces. Add *V* line numbers to the generated executable.
+  -cg               Same as -g, but add *C* line numbers to the generated executable instead of *V* line numbers.
+  -keep_c           Do NOT remove the generated .tmp.c files after compilation. 
+                    It is useful when using debuggers like gdb/visual studio, when given after -g / -cg .
+  -show_c_cmd       Print the full C compilation command and how much time it took.
   -cc <ccompiler>   Specify which C compiler you want to use as a C backend.
                     The C backend compiler should be able to handle C99 compatible C code.
                     Common C compilers are gcc, clang, tcc, icc, cl...
   -cflags <flags>   Pass additional C flags to the C backend compiler.
                     Example: -cflags `sdl2-config --cflags`
-  -debug            Keep the generated C file for debugging in program.tmp.c even after compilation.
-  -shared           Build a shared library.
-  -stats            Show additional stats when compiling/running tests. Try `v -stats test .`
-  -g                Show v line numbers in backtraces. Implies -debug.
-  -obf              Obfuscate the resulting binary.
-  -show_c_cmd       Print the full C compilation command and how much time it took.
-  -                 Shorthand for `v runrepl`.
 
+Commands:
   up                Update V. Run `v up` at least once per day, since V development is rapid and features/bugfixes are added constantly.
   run <file.v>      Build and execute the V program in file.v. You can add arguments for the V program *after* the file name.
   build <module>    Compile a module into an object file.