os: implement support for VOPEN_URI_CMD env override for os.open_uri

vlib/os/open_uri_default.c.v

@@ -1,32 +1,30 @@
 module os
 
 pub fn open_uri(uri string) ? {
+	mut vopen_uri_cmd := getenv('VOPEN_URI_CMD')
+	if vopen_uri_cmd == '' {
 		$if macos {
-		result := execute('open "$uri"')
-		if result.exit_code != 0 {
-			return error('unable to open url: $result.output')
-		}
+			vopen_uri_cmd = 'open'
 		} $else $if freebsd || openbsd {
-		result := execute('xdg-open "$uri"')
-		if result.exit_code != 0 {
-			return error('unable to open url: $result.output')
-		}
+			vopen_uri_cmd = 'xdg-open'
 		} $else $if linux {
 			providers := ['xdg-open', 'x-www-browser', 'www-browser', 'wslview']
-
 			// There are multiple possible providers to open a browser on linux
 			// One of them is xdg-open, another is x-www-browser, then there's www-browser, etc.
 			// Look for one that exists and run it
 			for provider in providers {
 				if exists_in_system_path(provider) {
-				result := execute('$provider "$uri"')
-				if result.exit_code != 0 {
-					return error('unable to open url: $result.output')
-				}
+					vopen_uri_cmd = provider
 					break
 				}
 			}
-	} $else {
+		}
+	}
+	if vopen_uri_cmd == '' {
 		return error('unsupported platform')
 	}
+	result := execute('$vopen_uri_cmd "$uri"')
+	if result.exit_code != 0 {
+		return error('unable to open url: $result.output')
+	}
 }

vlib/os/open_uri_windows.c.v

@@ -5,6 +5,14 @@ import dl
 type ShellExecuteWin = fn (voidptr, &u16, &u16, &u16, &u16, int)
 
 pub fn open_uri(uri string) ? {
+	mut vopen_uri_cmd := getenv('VOPEN_URI_CMD')
+	if vopen_uri_cmd != '' {
+		result := execute('$vopen_uri_cmd "$uri"')
+		if result.exit_code != 0 {
+			return error('unable to open url: $result.output')
+		}
+		return
+	}
 	handle := dl.open_opt('shell32', dl.rtld_now) ?
 	// https://docs.microsoft.com/en-us/windows/win32/api/shellapi/nf-shellapi-shellexecutew
 	func := ShellExecuteWin(dl.sym_opt(handle, 'ShellExecuteW') ?)