Fix error message for assigning to non-null properties.

instead of falling down to "Required property 'a' missing at $"

kotlin-codegen/compiler/src/main/java/com/squareup/moshi/AdapterGenerator.kt

@@ -181,13 +181,27 @@ internal class AdapterGenerator(
     propertyList.forEachIndexed { index, property ->
       if (property.differentiateAbsentFromNull) {
         result.beginControlFlow("%L -> ", index)
-        result.addStatement("%N = %N.fromJson(%N)",
+        if (property.delegateKey.nullable) {
-            property.localName, nameAllocator.get(property.delegateKey), readerParam)
+          result.addStatement("%N = %N.fromJson(%N)",
+              property.localName, nameAllocator.get(property.delegateKey), readerParam)
+        } else {
+          result.addStatement("%N = %N.fromJson(%N)" +
+              " ?: throw %T(\"Non-null value '%N' was null at \${%N.path}\")",
+              property.localName, nameAllocator.get(property.delegateKey), readerParam,
+              JsonDataException::class, property.localName, readerParam)
+        }
         result.addStatement("%N = true", property.localIsPresentName)
         result.endControlFlow()
       } else {
-        result.addStatement("%L -> %N = %N.fromJson(%N)",
+        if (property.delegateKey.nullable) {
-            index, property.localName, nameAllocator.get(property.delegateKey), readerParam)
+          result.addStatement("%L -> %N = %N.fromJson(%N)",
+              index, property.localName, nameAllocator.get(property.delegateKey), readerParam)
+        } else {
+          result.addStatement("%L -> %N = %N.fromJson(%N)" +
+              " ?: throw %T(\"Non-null value '%N' was null at \${%N.path}\")",
+              index, property.localName, nameAllocator.get(property.delegateKey), readerParam,
+              JsonDataException::class, property.localName, readerParam)
+        }
       }
     }
 

kotlin-codegen/integration-test/src/test/kotlin/com/squareup/moshi/GeneratedAdaptersTest.kt

@@ -383,6 +383,20 @@ class GeneratedAdaptersTest {
     }
   }
 
+  @Test fun nonNullConstructorParameterCalledWithNullFromAdapterFailsWithJsonDataException() {
+    val moshi = Moshi.Builder().add(object {
+      @FromJson fun fromJson(string: String): String? = null
+    }).build()
+    val jsonAdapter = moshi.adapter(HasNonNullConstructorParameter::class.java)
+
+    try {
+      jsonAdapter.fromJson("{\"a\":\"hello\"}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
+    }
+  }
+
   @JsonClass(generateAdapter = true)
   class HasNonNullConstructorParameter(val a: String)
 
@@ -539,6 +553,20 @@ class GeneratedAdaptersTest {
     }
   }
 
+  @Test fun nonNullPropertySetToNullFromAdapterFailsWithJsonDataException() {
+    val moshi = Moshi.Builder().add(object {
+      @FromJson fun fromJson(string: String): String? = null
+    }).build()
+    val jsonAdapter = moshi.adapter(HasNonNullProperty::class.java)
+
+    try {
+      jsonAdapter.fromJson("{\"a\":\"hello\"}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$.a")
+    }
+  }
+
   @JsonClass(generateAdapter = true)
   class HasNonNullProperty {
     var a: String = ""

kotlin/src/test/java/com/squareup/moshi/kotlin/KotlinJsonAdapterTest.kt

@@ -152,6 +152,20 @@ class KotlinJsonAdapterTest {
     }
   }
 
+  @Test fun nonNullConstructorParameterCalledWithNullFromAdapterFailsWithJsonDataException() {
+    val moshi = Moshi.Builder().add(object {
+      @FromJson fun fromJson(string: String): String? = null
+    }).add(KotlinJsonAdapterFactory()).build()
+    val jsonAdapter = moshi.adapter(HasNonNullConstructorParameter::class.java)
+
+    try {
+      jsonAdapter.fromJson("{\"a\":\"hello\"}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$")
+    }
+  }
+
   class HasNonNullConstructorParameter(val a: String)
 
   @Test fun nonNullPropertySetToNullFailsWithJsonDataException() {
@@ -166,6 +180,20 @@ class KotlinJsonAdapterTest {
     }
   }
 
+  @Test fun nonNullPropertySetToNullFromAdapterFailsWithJsonDataException() {
+    val moshi = Moshi.Builder().add(object {
+      @FromJson fun fromJson(string: String): String? = null
+    }).add(KotlinJsonAdapterFactory()).build()
+    val jsonAdapter = moshi.adapter(HasNonNullProperty::class.java)
+
+    try {
+      jsonAdapter.fromJson("{\"a\":\"hello\"}")
+      fail()
+    } catch (expected: JsonDataException) {
+      assertThat(expected).hasMessage("Non-null value 'a' was null at \$")
+    }
+  }
+
   class HasNonNullProperty {
     var a: String = ""
   }