Avoid StackOverflow in code generation by dispatching a real error

When a callback expression returns void but it is expected to return a
value, data binding goes into an infinite loop because it tries to find
a value but cannot because void cannot be a assigned to a variable.

The right fix here would be to check for assignability and throw a
better error message but it might break some existing apps because i
don't trust our assignability checks. Instead, this CL covers the void
return type case to fix this one bug without taking a bigger risk.

Fixes: 123260053
Test: SimpleCompilationTest.testCallbackReturnTypeMismatch

Change-Id: Ie9b4d03e0e2d818a0613f4cdefc470e1f7221b27

1 files changed, 12 insertions, 0 deletions

diff --git a/compilerCommon/src/main/java/android/databinding/tool/processing/ErrorMessages.java b/compilerCommon/src/main/java/android/databinding/tool/processing/ErrorMessages.java
index 25e3a852..93d6f92c 100644
--- a/compilerCommon/src/main/java/android/databinding/tool/processing/ErrorMessages.java
+++ b/compilerCommon/src/main/java/android/databinding/tool/processing/ErrorMessages.java
@@ -83,6 +83,18 @@ public class ErrorMessages {
             "'%s::%s' accepts %d parameter(s), but the assigned expression uses %d parameter(s). The expression should have no " +
             "parameters or an equal number of parameters.";
 
+    public static String callbackReturnTypeMismatchError(
+        String methodName,
+        String expectedReturnType,
+        String expression,
+        String expressionReturnType
+    ) {
+        return "Invalid return type in callback.\n"
+               + "Callback method `" + methodName + "` is expected to return `"
+               + expectedReturnType + "` but expression `"
+               + expression + "` returns `" + expressionReturnType + "`";
+    }
+
     public static final String DUPLICATE_CALLBACK_ARGUMENT =
             "Callback parameter '%s' is not unique";