Changes on PR feedback

Check rustup on common installation paths and user's $PATH or %PATH%

Author: TranceLove

gradle/setupRustAndroidLocal.gradle

@@ -7,10 +7,30 @@ tasks.register("setupRustAndroidLocal") {
     }
 
     // Detect existence of rustup.
-    def rustupExists = exec {
-        commandLine("which", "rustup")
-        ignoreExitValue true
-    }.exitValue == 0
+    def rustupExists = {
+
+        // First check common installation path
+        def isWindows = System.getProperty("os.name").toLowerCase().contains("windows")
+        def home = System.getProperty("user.home")
+        def rustupPath = isWindows
+            ? new File(home, ".cargo/bin/rustup.exe")
+            : new File(home, ".cargo/bin/rustup")
+
+        if (rustupPath.exists() && rustupPath.canExecute()) {
+            return true
+        }
+
+        // If not, check on user $PATH/%PATH%
+        try {
+            def process = new ProcessBuilder("rustup")
+                .redirectErrorStream(true)
+                .start()
+            process.waitFor()
+            return process.exitValue() == 0
+        } catch (IOException ignored) {
+            return false
+        }
+    }()
 
     if (!rustupExists) {
         println("rustup not found. Installing rustup...")