all: support ./v -exclude @vlib/math/*.c.v vlib/math/math_test.v, for using the pure V math module implementation, without the .c.v overrides there. (#19290)

vlib/v/help/build/build.txt

@@ -77,6 +77,17 @@ NB: the build flags are shared with the run command too:
       -path "/v/my_project_private_modules|@vlib|@vmodules"
     By default, -path is just "@vlib|@vmodules" .
 
+  -exclude
+    Specify an exclude pattern that will be applied as a filter over the full paths of the .v
+    files, that otherwise would have been selected for compilation.
+    Note:
+       @vroot is expanded to the location, where the v executable is.
+       @vlib is expanded do the location where your vlib/ folder is (next to your v executable).
+       @vmodules is expanded with the location of your ~/.vmodules/ folder.
+    Example:
+       `./v -exclude @vlib/math/*.c.v vlib/math/math_test.v`
+            ^ run the math test file, using only pure .v files, excluding the .c.v overrides.
+
   -prod
     Compile the executable in production mode, where most optimizations are enabled.
     Note that most V warnings turn to errors, if you pass -prod, so you will have

vlib/v/pref/default.v

@@ -6,9 +6,7 @@ module pref
 import os
 import v.vcache
 
-pub const (
-	default_module_path = os.vmodules_dir()
-)
+pub const default_module_path = os.vmodules_dir()
 
 pub fn new_preferences() &Preferences {
 	mut p := &Preferences{}
@@ -21,26 +19,46 @@ fn (mut p Preferences) expand_lookup_paths() {
 		// Location of all vlib files
 		p.vroot = os.dir(vexe_path())
 	}
-	vlib_path := os.join_path(p.vroot, 'vlib')
+	p.vlib = os.join_path(p.vroot, 'vlib')
+	p.vmodules_paths = os.vmodules_paths()
+	//
 	if p.lookup_path.len == 0 {
 		p.lookup_path = ['@vlib', '@vmodules']
 	}
 	mut expanded_paths := []string{}
 	for path in p.lookup_path {
 		match path {
-			'@vlib' { expanded_paths << vlib_path }
-			'@vmodules' { expanded_paths << os.vmodules_paths() }
+			'@vlib' { expanded_paths << p.vlib }
+			'@vmodules' { expanded_paths << p.vmodules_paths }
 			else { expanded_paths << path }
 		}
 	}
 	p.lookup_path = expanded_paths
 }
 
+fn (mut p Preferences) expand_exclude_paths() {
+	mut res := []string{}
+	static_replacement_list := ['@vroot', p.vroot, '@vlib', p.vlib]
+	for x in p.exclude {
+		y := x.replace_each(static_replacement_list)
+		if y.contains('@vmodules') {
+			// @vmodules is a list of paths, each of which should be expanded in the complete exclusion list:
+			for vmp in p.vmodules_paths {
+				res << y.replace('@vmodules', vmp)
+			}
+			continue
+		}
+		res << y
+	}
+	p.exclude = res
+}
+
 pub fn (mut p Preferences) fill_with_defaults() {
 	if p.arch == ._auto {
 		p.arch = get_host_arch()
 	}
 	p.expand_lookup_paths()
+	p.expand_exclude_paths()
 	rpath := os.real_path(p.path)
 	if p.out_name == '' {
 		filename := os.file_name(rpath).trim_space()

vlib/v/pref/pref.v

@@ -184,12 +184,15 @@ pub mut:
 	output_es5       bool
 	prealloc         bool
 	vroot            string
+	vlib             string   // absolute path to the vlib/ folder
+	vmodules_paths   []string // absolute paths to the vmodules folders, by default ['/home/user/.vmodules'], can be overriden by setting VMODULES
 	out_name_c       string   // full os.real_path to the generated .tmp.c file; set by builder.
 	out_name         string
 	path             string // Path to file/folder to compile
 	line_info        string // `-line-info="file.v:28"`: for "mini VLS" (shows information about objects on provided line)
 	//
 	run_only []string // VTEST_ONLY_FN and -run-only accept comma separated glob patterns.
+	exclude  []string // glob patterns for excluding .v files from the list of .v files that otherwise would have been used for a compilation, example: `-exclude @vlib/math/*.c.v`
 	// Only test_ functions that match these patterns will be run. -run-only is valid only for _test.v files.
 	//
 	// -d vfmt and -d another=0 for `$if vfmt { will execute }` and `$if another ? { will NOT get here }`
@@ -620,6 +623,11 @@ pub fn parse_args_and_show_errors(known_external_commands []string, args []strin
 				res.run_only = cmdline.option(current_args, arg, os.getenv('VTEST_ONLY_FN')).split_any(',')
 				i++
 			}
+			'-exclude' {
+				patterns := cmdline.option(current_args, arg, '').split_any(',')
+				res.exclude << patterns
+				i++
+			}
 			'-test-runner' {
 				res.test_runner = cmdline.option(current_args, arg, res.test_runner)
 				i++

vlib/v/pref/should_compile.v

@@ -7,7 +7,7 @@ pub fn (prefs &Preferences) should_compile_filtered_files(dir string, files_ []s
 	mut files := files_.clone()
 	files.sort()
 	mut all_v_files := []string{}
-	for file in files {
+	files_loop: for file in files {
 		if !file.ends_with('.v') && !file.ends_with('.vh') {
 			continue
 		}
@@ -75,6 +75,14 @@ pub fn (prefs &Preferences) should_compile_filtered_files(dir string, files_ []s
 				continue
 			}
 		}
+		if prefs.exclude.len > 0 {
+			full_file_path := os.join_path(dir, file)
+			for epattern in prefs.exclude {
+				if full_file_path.match_glob(epattern) {
+					continue files_loop
+				}
+			}
+		}
 		all_v_files << os.join_path(dir, file)
 	}
 	//