v.vcache: store the cache files in ~/.vmodules/_cache by default, all…

…owing for user modules, that are named `cache` (fix #22459)

vlib/v/tests/projects_that_should_compile_test.v

@@ -28,4 +28,7 @@ fn test_projects_should_run() {
 
 	res2 := vrun_ok('run', vroot_path('vlib/v/tests/testdata/modules_in_src/'))
 	assert res2.trim_space() == 'somemodule somemoduletwo'
+
+	res3 := vrun_ok('run', vroot_path('vlib/v/tests/testdata/module_named_cache/'))
+	assert res3.trim_space().ends_with('cache.a: 123')
 }

vlib/v/tests/testdata/module_named_cache/src/cache/my_cache.v

@@ -0,0 +1,3 @@
+module cache
+
+pub const a = 123

vlib/v/tests/testdata/module_named_cache/src/main.v

@@ -0,0 +1,8 @@
+module main
+
+import cache
+
+fn main() {
+	println('Hello World!')
+	dump(cache.a)
+}

vlib/v/tests/testdata/module_named_cache/v.mod

@@ -0,0 +1,7 @@
+Module {
+	name: 'aa'
+	description: 'AA'
+	version: '0.0.0'
+	license: 'MIT'
+	dependencies: []
+}

vlib/v/vcache/vcache.v

@@ -37,7 +37,7 @@ pub mut:
 pub fn new_cache_manager(opts []string) CacheManager {
 	mut vcache_basepath := os.getenv('VCACHE')
 	if vcache_basepath == '' {
-		vcache_basepath = os.join_path(os.vmodules_dir(), 'cache')
+		vcache_basepath = os.join_path(os.vmodules_dir(), '_cache') // use a path, that would not conflict with a user installable module
 	}
 	nlog(@FN, 'vcache_basepath: ${vcache_basepath}\n         opts: ${opts}\n      os.args: ${os.args.join(' ')}')
 	dlog(@FN, 'vcache_basepath: ${vcache_basepath} | opts:\n     ${opts}')