JetBrains/intellij-community · error · EvaluateRuntimeException

Local variable declarations are not supported here.

Error message

Local variable declarations are not supported here.

What it means

Thrown by EvaluatorBuilderImpl when the evaluated code fragment contains a local variable declaration statement but the current evaluation mode/context does not support declaring new locals (e.g. a single-expression evaluator or a context where only statements/expressions are allowed). The builder explicitly rejects the declaration instead of failing later at runtime.

Source

Thrown at java/debugger/impl/src/com/intellij/debugger/engine/evaluation/expression/EvaluatorBuilderImpl.java:868

                Evaluator rEvaluator = myResult;

                PsiExpression localVarReference = elementFactory.createExpressionFromText(localVariable.getName(), initializer);

                localVarReference.accept(this);
                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;
      }
    }

View on GitHub (pinned to be881553f2)

Solutions

1. Enable 'Code fragment mode' / 'Enable new variables' in the Evaluate dialog so declarations are allowed
2. Rewrite the evaluation as a single expression without declarations (e.g. inline the value)
3. Use a watcher with pre-declared variables instead of declaring new ones

Example fix

// before (expression mode): int x = 5; x * 2;

// after (expression mode): 5 * 2;
// or: switch the Evaluate dialog to Code fragment mode

// when driving evaluation programmatically
if (mode.allowsCodeFragments() || !containsDeclarations(expressionText)) {
  evaluator = EvaluatorBuilder.build(fragment, mode);
} else {
  evaluator = EvaluatorBuilder.build(stripDeclarations(expressionText), EXPRESSION_MODE);
}

try {
  textUI.evaluate(input);
} catch (EvaluateRuntimeException e) {
  // if 'declarations not supported', retry with declarations inlined/removed
}

When it happens

Trigger: Visiting a PsiDeclarationStatement in a code fragment evaluated in 'expression' mode (Alt+F8 Evaluate Expression without 'code fragment' mode enabled), or an API-driven evaluation built with EvaluatorBuilder without fragment support; the else branch throws EvaluateRuntimeException with evaluation.error.local.variable.declarations.not.supported.

Common situations: User types 'int x = 5;' into the Evaluate dialog while it is configured as a single expression instead of a code fragment; evaluating declarations in a watcher or inline evaluator that only accepts expressions.

Related errors

• Interface method invocation is not supported in JVM {}. Use
• Cannot construct wrapper object for value of type {}: Unable
• Variable ''{0}'' is already declared
• Invalid declaration : {0} Only local variable declarations a
• inconvertible.type.cast

AI-assisted analysis of JetBrains/intellij-community@be881553f2 (2026-08-14). Data as JSON: /api/errors/5bf667d2db2dad77. Report an issue: GitHub.