Report error better (when encountered weird ndk installation)

Author: iacore

ndk-build/src/error.rs

@@ -8,13 +8,13 @@ use thiserror::Error;
 pub enum NdkError {
     #[error(
         "Android SDK is not found. \
-    Please set the path to the Android SDK with the $ANDROID_SDK_ROOT \
+    Please set the path to the Android SDK with the $ANDROID_HOME \
     environment variable."
     )]
     SdkNotFound,
     #[error(
         "Android NDK is not found. \
-        Please set the path to the Android NDK with $ANDROID_NDK_ROOT \
+        Please set the path to the Android NDK with $NDK_HOME \
         environment variable."
     )]
     NdkNotFound,

ndk-build/src/ndk.rs

@@ -85,8 +85,10 @@ impl Ndk {
             .max()
             .ok_or(NdkError::BuildToolsNotFound)?;
 
-        let build_tag = std::fs::read_to_string(ndk_path.join("source.properties"))
-            .expect("Failed to read source.properties");
+        let Ok(build_tag) = std::fs::read_to_string(ndk_path.join("source.properties")) else {
+            eprintln!("Failed to read source.properties. Maybe NDK is not at {:?}.", ndk_path);
+            return Err(NdkError::NdkNotFound);
+        };
 
         let build_tag = build_tag
             .split('\n')