Ensure Glean does not initialize with an empty application id

Using an empty application id makes it impossible to upload pings
to ingestion, since the application id is used to build the submission
path.

glean-core/src/error.rs

@@ -54,6 +54,9 @@ pub enum ErrorKind {
     /// Unknown error
     Utf8Error,
 
+    /// Glean initialization was attempted with an invalid configuration
+    InvalidConfig,
+
     /// Glean not initialized
     NotInitialized,
 
@@ -103,6 +106,7 @@ impl Display for Error {
             HistogramType(h) => write!(f, "HistogramType conversion from {} failed", h),
             OsString(s) => write!(f, "OsString conversion from {:?} failed", s),
             Utf8Error => write!(f, "Invalid UTF-8 byte sequence in string"),
+            InvalidConfig => write!(f, "Invalid Glean configuration provided"),
             NotInitialized => write!(f, "Global Glean object missing"),
             __NonExhaustive => write!(f, "Unknown error"),
         }

glean-core/src/lib.rs

@@ -42,7 +42,7 @@ mod util;
 
 pub use crate::common_metric_data::{CommonMetricData, Lifetime};
 use crate::database::Database;
-pub use crate::error::{Error, Result};
+pub use crate::error::{Error, ErrorKind, Result};
 pub use crate::error_recording::{test_get_num_recorded_errors, ErrorType};
 use crate::event_database::EventDatabase;
 use crate::internal_metrics::CoreMetrics;
@@ -188,6 +188,9 @@ impl Glean {
         log::info!("Creating new Glean v{}", GLEAN_VERSION);
 
         let application_id = sanitize_application_id(&cfg.application_id);
+        if application_id.is_empty() {
+            return Err(ErrorKind::InvalidConfig.into());
+        }
 
         // Creating the data store creates the necessary path as well.
         // If that fails we bail out and don't initialize further.

glean-core/src/lib_unit_tests.rs

@@ -778,3 +778,14 @@ fn test_setting_debug_view_tag() {
     assert_eq!(false, glean.set_debug_view_tag(invalid_tag));
     assert_eq!(valid_tag, glean.debug_view_tag().unwrap());
 }
+
+#[test]
+#[should_panic]
+fn test_empty_application_id() {
+    let dir = tempfile::tempdir().unwrap();
+    let tmpname = dir.path().display().to_string();
+
+    let glean = Glean::with_options(&tmpname, "", true).unwrap();
+    // Check that this is indeed the first run.
+    assert!(glean.is_first_run());
+}