JetBrains/intellij-community · error · EvaluateRuntimeException

Invalid declaration : {0} Only local variable declarations a

Error message

Invalid declaration : {0} Only local variable declarations are supported.

What it means

Thrown by EvaluatorBuilderImpl when a PsiDeclarationStatement contains an element that is not a local variable — for example a class, enum, or field declaration inside an evaluated fragment. Only local variable declarations are supported by the JVM debugger's expression compiler, so anything else is rejected with the offending source text included in the message.

Source

Thrown at java/debugger/impl/src/com/intellij/debugger/engine/evaluation/expression/EvaluatorBuilderImpl.java:873

                Evaluator lEvaluator = myResult;
                rEvaluator = handleAssignmentBoxingAndPrimitiveTypeConversions(localVarReference.getType(), rType, rEvaluator,
                                                                               statement.getProject());

                Evaluator assignment = new AssignmentEvaluator(lEvaluator, rEvaluator);
                evaluators.add(assignment);
              }
              catch (IncorrectOperationException e) {
                LOG.error(e);
              }
            }
          }
          else {
            throw new EvaluateRuntimeException(new EvaluateException(
              JavaDebuggerBundle.message("evaluation.error.local.variable.declarations.not.supported"), null));
          }
        }
        else {
          throw new EvaluateRuntimeException(new EvaluateException(
            JavaDebuggerBundle.message("evaluation.error.unsupported.declaration", declaredElement.getText()), null));
        }
      }

      if (!evaluators.isEmpty()) {
        CodeFragmentEvaluator codeFragmentEvaluator = new CodeFragmentEvaluator(myCurrentFragmentEvaluator);
        codeFragmentEvaluator.setStatements(evaluators.toArray(new Evaluator[0]));
        myResult = codeFragmentEvaluator;
      }
      else {
        myResult = null;
      }
    }

    @Override
    public void visitConditionalExpression(@NotNull PsiConditionalExpression expression) {
      if (LOG.isDebugEnabled()) {
        LOG.debug("visitConditionalExpression " + expression);

View on GitHub (pinned to be881553f2)

Solutions

Remove nested type declarations from the evaluated fragment; declare the type in real project code instead
Replace the local class usage with an existing project class or a lambda/anonymous expression
Perform the setup in the actual source and re-run to the breakpoint

Example fix

// before (fragment): class Pair { int a, b; }
new Pair()

// after (fragment): java.util.List.of(1, 2)

Defensive patterns

Strategy: validation

Validate before calling

for (PsiElement el : declarationStatement.getDeclaredElements()) {
  if (!(el instanceof PsiLocalVariable)) {
    throw new UnsupportedOperationException("Only local variable declarations are supported: " + el.getText());
  }
}

Type guard

boolean isSupportedDeclaration(PsiDeclarationStatement s) {
  return Arrays.stream(s.getDeclaredElements()).allMatch(e -> e instanceof PsiLocalVariable);
}

Try / catch

try {
  builder.visitElement(fragment);
} catch (EvaluateRuntimeException e) {
  // strip class/enum declarations and re-evaluate
}

Prevention

Keep type declarations out of evaluated fragments
Declare helper types in project source before debugging
Substitute lambdas or existing classes for local classes in evaluations

When it happens

Trigger: Visiting a declaration statement whose declaredElement is not a PsiLocalVariable (inner class declaration, local enum/interface/record in the fragment, annotation-type declaration); the builder falls to the else branch and throws evaluation.error.unsupported.declaration with declaredElement.getText().

Common situations: User pastes a code snippet containing 'class Foo { ... }' or 'enum E { A }' into the Evaluate code-fragment dialog; evaluating fragments that declare local records (Java 16+) which the evaluator cannot compile.

Related errors

AI-assisted analysis of JetBrains/intellij-community@be881553f2 (2026-08-14). Data as JSON: /api/errors/8d1c322c72e241bd. Report an issue: GitHub.