testing: allow tests to import the same module with no custom options

vlib/compiler/main.v

@@ -77,6 +77,7 @@ pub mut:
 	file_parser_idx map[string]int // map absolute file path to v.parsers index
 	gen_parser_idx  map[string]int
 	cached_mods []string
+	module_lookup_paths []string
 }
 
 struct Preferences {
@@ -641,23 +642,28 @@ pub fn (v &V) v_files_from_dir(dir string) []string {
 		if file.ends_with('_c.v') && v.os == .js {
 			continue
 		}
-		res << '$dir${os.path_separator}$file'
+		res << filepath.join(dir,file)
 	}
 	return res
 }
 
 // Parses imports, adds necessary libs, and then user files
 pub fn (v mut V) add_v_files_to_compile() {
+	v.set_module_lookup_paths()
 	mut builtin_files := v.get_builtin_files()
 	if v.pref.is_bare {
 		//builtin_files = []
 	}
 	// Builtin cache exists? Use it.
-	builtin_vh := '${v.pref.vlib_path}${os.path_separator}builtin.vh'
-	if v.pref.is_cache && os.exists(builtin_vh) {
+	if v.pref.is_cache {
+		builtin_vh := filepath.join(v_modules_path,'vlib','builtin.vh')
+		if os.exists(builtin_vh) {
 			v.cached_mods << 'builtin'
 			builtin_files = [builtin_vh]
 		}
+	}
+	if v.pref.is_verbose { v.log('v.add_v_files_to_compile > builtin_files: $builtin_files') }
+	
 	// Parse builtin imports
 	for file in builtin_files {
 		// add builtins first
@@ -768,11 +774,13 @@ pub fn (v &V)  get_user_files() []string {
 		}
 	}
 	if dir.ends_with('.v') || dir.ends_with('.vsh') {
+		single_v_file := dir
 		// Just compile one file and get parent dir
-		user_files << dir
-		dir = dir.all_before(os.path_separator)
+		user_files << single_v_file
+		if v.pref.is_verbose { v.log('> just compile one file: "${single_v_file}"') }
 	}
 	else {
+		if v.pref.is_verbose { v.log('> add all .v files from directory "${dir}" ...') }
 		// Add .v files from the directory being compiled
 		files := v.v_files_from_dir(dir)
 		for file in files {
@@ -784,8 +792,7 @@ pub fn (v &V)  get_user_files() []string {
 		exit(1)
 	}
 	if v.pref.is_verbose {
-		v.log('user_files:')
-		println(user_files)
+		v.log('user_files: $user_files')
 	}
 	return user_files
 }

vlib/compiler/modules.v

@@ -150,27 +150,45 @@ pub fn(graph &DepGraph) imports() []string {
 // 'strings' => 'VROOT/vlib/strings'
 // 'installed_mod' => '~/.vmodules/installed_mod'
 // 'local_mod' => '/path/to/current/dir/local_mod'
-fn (v &V) find_module_path(mod string) ?string {
+
+fn (v mut V) set_module_lookup_paths(){
+	mlookup_path := if v.pref.vpath.len>0{ v.pref.vpath }else{ v_modules_path }
 	// Module search order:
+	// 0) V test files are very commonly located right inside the folder of the
+	// module, which they test. Adding the parent folder of the module folder
+	// with the _test.v files, *guarantees* that the tested module can be found
+	// without needing to set custom options/flags.
+	
 	// 1) search in the *same* directory, as the compiled final v program source
 	//    (i.e. the . in `v .` or file.v in `v file.v`)
 	// 2) search in the modules/ in the same directory.
 	// 3) search in vlib/
 	// 4.1) search in -vpath (if given)
 	// 4.2) search in ~/.vmodules/ (i.e. modules installed with vpm) (no -vpath)
-	modules_lookup_path := if v.pref.vpath.len > 0 { v.pref.vpath } else { v_modules_path }
-	mod_path := v.module_path(mod)
-	mut tried_paths := []string
-	tried_paths << filepath.join(v.compiled_dir, mod_path)
-	tried_paths << filepath.join(v.compiled_dir, 'modules', mod_path)
-	tried_paths << filepath.join(v.pref.vlib_path, mod_path)
-	tried_paths << filepath.join(modules_lookup_path, mod_path)
-	if v.pref.user_mod_path.len > 0 {
-		tried_paths << filepath.join(v.pref.user_mod_path, mod_path)
+	v.module_lookup_paths = []	
+	if v.pref.is_test {
+		v.module_lookup_paths << os.basedir(v.compiled_dir) // pdir of _test.v
 	}
-	for try_path in tried_paths {
+	v.module_lookup_paths << v.compiled_dir
+	v.module_lookup_paths << filepath.join(v.compiled_dir, 'modules')
+	v.module_lookup_paths << v.pref.vlib_path
+	v.module_lookup_paths << mlookup_path
+	if v.pref.user_mod_path.len > 0 {
+		v.module_lookup_paths << v.pref.user_mod_path
+	}
+
+	if v.pref.is_verbose {
+		v.log('v.module_lookup_paths: $v.module_lookup_paths')
+	}
+}
+
+fn (v &V) find_module_path(mod string) ?string {
+	mod_path := v.module_path(mod)
+	for lookup_path in v.module_lookup_paths {
+		try_path := filepath.join(lookup_path, mod_path)
 		if v.pref.is_verbose { println('  >> trying to find $mod in $try_path ...') }
 		if os.is_dir(try_path) {
+			if v.pref.is_verbose { println('  << found $try_path .') }
 			return try_path 
 		}
 	}

vlib/compiler/tests/modules/simplemodule/importing_test.v

@@ -0,0 +1,11 @@
+import simplemodule
+
+// this tests whether the tests can import the same module without any special
+// custom paths setup on the CLI
+fn test_iadd(){
+	assert simplemodule.iadd(10, 20) == 30
+}
+
+fn test_imul(){
+	assert simplemodule.imul(5,8) == 40
+}

vlib/compiler/tests/modules/simplemodule/simplemodule.v

@@ -0,0 +1,9 @@
+module simplemodule
+
+pub fn iadd(x int, y int) int {
+	return x + y
+}
+
+pub fn imul(x int, y int) int {
+	return x * y
+}