Report an error when a potentially non-nullable local variable is not initialized.

[email protected], [email protected]

Change-Id: Ie1d148ff584c202edc334659eeb4f792bb8773d4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/106620
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: scheglov

pkg/analyzer/lib/error/error.dart

@@ -236,6 +236,7 @@ const List<ErrorCode> errorCodeValues = const [
   CompileTimeErrorCode.NON_GENERATIVE_CONSTRUCTOR,
   CompileTimeErrorCode.NON_SYNC_FACTORY,
   CompileTimeErrorCode.NOT_ENOUGH_REQUIRED_ARGUMENTS,
+  CompileTimeErrorCode.NOT_INITIALIZED_POTENTIALLY_NON_NULLABLE_LOCAL_VARIABLE,
   CompileTimeErrorCode.NOT_ITERABLE_SPREAD,
   CompileTimeErrorCode.NOT_MAP_SPREAD,
   CompileTimeErrorCode.NOT_NULL_AWARE_NULL_SPREAD,

pkg/analyzer/lib/src/error/codes.dart

@@ -2452,6 +2452,22 @@ class CompileTimeErrorCode extends ErrorCode {
           "{0} required argument(s) expected, but {1} found.",
           correction: "Try adding the missing arguments.");
 
+  /**
+   * It is an error if a potentially non-nullable local variable which has no
+   * initializer expression and is not marked `late` is used before it is
+   * definitely assigned.
+   *
+   * TODO(scheglov) Update the code and the message when implement definite
+   * assignment analysis.
+   */
+  static const CompileTimeErrorCode
+      NOT_INITIALIZED_POTENTIALLY_NON_NULLABLE_LOCAL_VARIABLE =
+      const CompileTimeErrorCode(
+          'NOT_INITIALIZED_POTENTIALLY_NON_NULLABLE_LOCAL_VARIABLE',
+          "Non-nullable local variable '{0}' must be initialized.",
+          correction:
+              "Try giving it an initializer expression, or mark it 'late'.");
+
   /**
    * No parameters.
    */

pkg/analyzer/lib/src/generated/error_verifier.dart

@@ -1439,6 +1439,7 @@ class ErrorVerifier extends RecursiveAstVisitor<void> {
   @override
   void visitVariableDeclarationStatement(VariableDeclarationStatement node) {
     _checkForFinalNotInitialized(node.variables);
+    _checkForNotInitializedPotentiallyNonNullableLocalVariable(node.variables);
     super.visitVariableDeclarationStatement(node);
   }
 
@@ -3367,6 +3368,43 @@ class ErrorVerifier extends RecursiveAstVisitor<void> {
     }
   }
 
+  void _checkForNotInitializedPotentiallyNonNullableLocalVariable(
+    VariableDeclarationList node,
+  ) {
+    // Const and final checked separately.
+    if (node.isConst || node.isFinal) {
+      return;
+    }
+
+    if (!_isNonNullable) {
+      return;
+    }
+
+    if (node.isLate) {
+      return;
+    }
+
+    if (node.type == null) {
+      return;
+    }
+    var type = node.type.type;
+
+    if (!_typeSystem.isPotentiallyNonNullable(type)) {
+      return;
+    }
+
+    for (var variable in node.variables) {
+      if (variable.initializer == null) {
+        _errorReporter.reportErrorForNode(
+          CompileTimeErrorCode
+              .NOT_INITIALIZED_POTENTIALLY_NON_NULLABLE_LOCAL_VARIABLE,
+          variable.name,
+          [variable.name.name],
+        );
+      }
+    }
+  }
+
   /**
    * If there are no constructors in the given [members], verify that all
    * final fields are initialized.  Cases in which there is at least one