fix bug where if NDK version isn't installed, you get a panic rather than a nice error message (#42)

fix bug raised on Github Issue #41 where if NDK version isn't installed, you get a panic rather than a nice error message

Fixes #41

Author: silbinarywolf

src/androidbuild/Ndk.zig

@@ -112,13 +112,9 @@ pub fn init(b: *std.Build, android_sdk_path: []const u8, ndk_version: []const u8
 }
 
 pub fn validateApiLevel(ndk: *const Ndk, b: *std.Build, api_level: ApiLevel, errors: *std.ArrayList([]const u8)) void {
-    // Get root jar path
-    const root_jar = b.pathResolve(&[_][]const u8{
-        ndk.android_sdk_path,
-        "platforms",
-        b.fmt("android-{d}", .{@intFromEnum(api_level)}),
-        "android.jar",
-    });
+    if (ndk.android_sdk_path.len == 0 or ndk.sysroot_path.len == 0) {
+        @panic("Should not call validateApiLevel if NDK path is not set");
+    }
 
     // Check if NDK sysroot/usr/lib/{target}/{api_level} path is accessible
     _ = blk: {
@@ -151,6 +147,13 @@ pub fn validateApiLevel(ndk: *const Ndk, b: *std.Build, api_level: ApiLevel, err
 
     // Check if platforms/android-{api-level}/android.jar exists
     _ = blk: {
+        // Get root jar path
+        const root_jar = b.pathResolve(&[_][]const u8{
+            ndk.android_sdk_path,
+            "platforms",
+            b.fmt("android-{d}", .{@intFromEnum(api_level)}),
+            "android.jar",
+        });
         std.fs.accessAbsolute(root_jar, .{}) catch |err| switch (err) {
             error.FileNotFound => {
                 const message = b.fmt("Android API level {d} not installed. Unable to find '{s}'", .{

src/androidbuild/apk.zig

@@ -71,7 +71,11 @@ pub fn create(sdk: *Sdk, options: Options) *Apk {
         error.NdkFailed => Ndk.empty, // fallthrough and print all errors below
         error.OutOfMemory => @panic("OOM"),
     };
-    ndk.validateApiLevel(b, options.api_level, &errors);
+    if (ndk.path.len != 0) {
+        // Only do additional NDK validation if ndk is not set to Ndk.empty
+        // ie. "ndk_version" isn't installed
+        ndk.validateApiLevel(b, options.api_level, &errors);
+    }
     if (errors.items.len > 0) {
         printErrorsAndExit("unable to find required Android installation", errors.items);
     }