http://www.eclipse.org/platform: Core Variables (Eclipse Foundation) 
Copyright (c) 2000, 2016 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation

/*******************************************************************************
 * Copyright (c) 2000, 2016 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.core.internal.variables;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Stack;

import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Status;
import org.eclipse.core.variables.IDynamicVariable;
import org.eclipse.core.variables.IStringVariableManager;
import org.eclipse.core.variables.IValueVariable;
import org.eclipse.core.variables.VariablesPlugin;
import org.eclipse.osgi.util.NLS;


Performs string substitution for context and value variables.

/**
 * Performs string substitution for context and value variables.
 */
public class StringSubstitutionEngine {

	// delimiters
	private static final String VARIABLE_START = "${"; //$NON-NLS-1$
	private static final char VARIABLE_END = '}';
	private static final char VARIABLE_ARG = ':';
	// parsing states
	private static final int SCAN_FOR_START = 0;
	private static final int SCAN_FOR_END = 1;

	
Resulting string

/**
	 * Resulting string
	 */
	private StringBuilder fResult;

	
Whether substitutions were performed

/**
	 * Whether substitutions were performed
	 */
	private boolean fSubs;

	
Stack of variables to resolve

/**
	 * Stack of variables to resolve
	 */
	private Stack<VariableReference> fStack;

	class VariableReference {

		// the text inside the variable reference
		private StringBuilder fText;

		public VariableReference() {
			fText = new StringBuilder();
		}

		public void append(String text) {
			fText.append(text);
		}

		public String getText() {
			return fText.toString();
		}

	}

	
Performs recursive string substitution and returns the resulting string.

Params:
  • expression – expression to resolve
  • reportUndefinedVariables – whether to report undefined variables as an error
  • resolveVariables – if the variables should be resolved during the substitution
  • manager – registry of variables
Throws:
  • CoreException – if unable to resolve a referenced variable or if a cycle exists
 in referenced variables
Returns:the resulting string with all variables recursively
 substituted
/**
	 * Performs recursive string substitution and returns the resulting string.
	 *
	 * @param expression expression to resolve
	 * @param reportUndefinedVariables whether to report undefined variables as an error
	 * @param resolveVariables if the variables should be resolved during the substitution
	 * @param manager registry of variables
	 * @return the resulting string with all variables recursively
	 *  substituted
	 * @exception CoreException if unable to resolve a referenced variable or if a cycle exists
	 *  in referenced variables
	 */
	public String performStringSubstitution(String expression, boolean reportUndefinedVariables, boolean resolveVariables, IStringVariableManager manager) throws CoreException {
		substitute(expression, reportUndefinedVariables, resolveVariables, manager);
		List<HashSet<String>> resolvedVariableSets = new ArrayList<>();
		while (fSubs) {
			HashSet<String> resolved = substitute(fResult.toString(), reportUndefinedVariables, true, manager);
			for(int i=resolvedVariableSets.size()-1; i>=0; i--) {
				HashSet<String> prevSet = resolvedVariableSets.get(i);
				if (prevSet.equals(resolved)) {
					HashSet<String> conflictingSet = new HashSet<>();
					for (; i<resolvedVariableSets.size(); i++) {
						conflictingSet.addAll(resolvedVariableSets.get(i));
					}
					StringBuilder problemVariableList = new StringBuilder();
					for (String string : conflictingSet) {
						problemVariableList.append(string);
						problemVariableList.append(", "); //$NON-NLS-1$
					}
					problemVariableList.setLength(problemVariableList.length()-2); //truncate the last ", "
					throw new CoreException(new Status(IStatus.ERROR, VariablesPlugin.getUniqueIdentifier(), VariablesPlugin.REFERENCE_CYCLE_ERROR, NLS.bind(VariablesMessages.StringSubstitutionEngine_4, new String[]{problemVariableList.toString()}), null));
				}
			}

			resolvedVariableSets.add(resolved);
		}
		return fResult.toString();
	}

	
Performs recursive string validation to ensure that all of the variables
contained in the expression exist

Params:
  • expression – expression to validate
  • manager – registry of variables
Throws:
  • CoreException – if a referenced variable does not exist or if a cycle exists
 in referenced variables
/**
	 * Performs recursive string validation to ensure that all of the variables
	 * contained in the expression exist
	 * @param expression expression to validate
	 * @param manager registry of variables
	 * @exception CoreException if a referenced variable does not exist or if a cycle exists
	 *  in referenced variables
	 */
	public void validateStringVariables(String expression, IStringVariableManager manager) throws CoreException {
		performStringSubstitution(expression, true, false, manager);
	}

	
Makes a substitution pass of the given expression returns a Set of the variables that were resolved in this
 pass

Params:
  • expression – source expression
  • reportUndefinedVariables – whether to report undefined variables as an error
  • resolveVariables – whether to resolve the value of any variables
  • manager – the IStringVariableManager to use for the substitution
Throws:
Returns:the set of Strings resolved from the given expression
/**
	 * Makes a substitution pass of the given expression returns a Set of the variables that were resolved in this
	 *  pass
	 *
	 * @param expression source expression
	 * @param reportUndefinedVariables whether to report undefined variables as an error
	 * @param resolveVariables whether to resolve the value of any variables
	 * @param manager the {@link IStringVariableManager} to use for the substitution
	 * @return the set of {@link String}s resolved from the given expression
	 * @exception CoreException if unable to resolve a variable
	 */
	private HashSet<String> substitute(String expression, boolean reportUndefinedVariables, boolean resolveVariables, IStringVariableManager manager) throws CoreException {
		fResult = new StringBuilder(expression.length());
		fStack = new Stack<>();
		fSubs = false;

		HashSet<String> resolvedVariables = new HashSet<>();

		int pos = 0;
		int state = SCAN_FOR_START;
		while (pos < expression.length()) {
			switch (state) {
				case SCAN_FOR_START:
					int start = expression.indexOf(VARIABLE_START, pos);
					if (start >= 0) {
						int length = start - pos;
						// copy non-variable text to the result
						if (length > 0) {
							fResult.append(expression.substring(pos, start));
						}
						pos = start + 2;
						state = SCAN_FOR_END;

						fStack.push(new VariableReference());
					} else {
						// done - no more variables
						fResult.append(expression.substring(pos));
						pos = expression.length();
					}
					break;
				case SCAN_FOR_END:
					// be careful of nested variables
					start = expression.indexOf(VARIABLE_START, pos);
					int end = expression.indexOf(VARIABLE_END, pos);
					if (end < 0) {
						// variables are not completed
						VariableReference tos = fStack.peek();
						tos.append(expression.substring(pos));
						pos = expression.length();
					} else {
						if (start >= 0 && start < end) {
							// start of a nested variable
							int length = start - pos;
							if (length > 0) {
								VariableReference tos = fStack.peek();
								tos.append(expression.substring(pos, start));
							}
							pos = start + 2;
							fStack.push(new VariableReference());
						} else {
							// end of variable reference
							VariableReference tos = fStack.pop();
							String substring = expression.substring(pos, end);
							tos.append(substring);
							resolvedVariables.add(substring);

							pos = end + 1;
							String value= resolve(tos, reportUndefinedVariables, resolveVariables, manager);
							if (value == null) {
								value = ""; //$NON-NLS-1$
							}
							if (fStack.isEmpty()) {
								// append to result
								fResult.append(value);
								state = SCAN_FOR_START;
							} else {
								// append to previous variable
								tos = fStack.peek();
								tos.append(value);
							}
						}
					}
					break;
				default:
					break;
			}
		}
		// process incomplete variable references
		while (!fStack.isEmpty()) {
			VariableReference tos = fStack.pop();
			if (fStack.isEmpty()) {
				fResult.append(VARIABLE_START);
				fResult.append(tos.getText());
			} else {
				VariableReference var = fStack.peek();
				var.append(VARIABLE_START);
				var.append(tos.getText());
			}
		}


		return resolvedVariables;
	}

	
Resolve and return the value of the given variable reference,
possibly null.

Params:
  • var – the VariableReference to try and resolve
  • reportUndefinedVariables – whether to report undefined variables as
 an error
  • resolveVariables – whether to resolve the variables value or just to validate that this variable is valid
  • manager – variable registry
Throws:
Returns:variable value, possibly null
/**
	 * Resolve and return the value of the given variable reference,
	 * possibly <code>null</code>.
	 *
	 * @param var the {@link VariableReference} to try and resolve
	 * @param reportUndefinedVariables whether to report undefined variables as
	 *  an error
	 * @param resolveVariables whether to resolve the variables value or just to validate that this variable is valid
	 * @param manager variable registry
	 * @return variable value, possibly <code>null</code>
	 * @exception CoreException if unable to resolve a value
	 */
	private String resolve(VariableReference var, boolean reportUndefinedVariables, boolean resolveVariables, IStringVariableManager manager) throws CoreException {
		String text = var.getText();
		int pos = text.indexOf(VARIABLE_ARG);
		String name = null;
		String arg = null;
		if (pos > 0) {
			name = text.substring(0, pos);
			pos++;
			if (pos < text.length()) {
				arg = text.substring(pos);
			}
		} else {
			name = text;
		}
		IValueVariable valueVariable = manager.getValueVariable(name);
		if (valueVariable == null) {
			IDynamicVariable dynamicVariable = manager.getDynamicVariable(name);
			if (dynamicVariable == null) {
				// no variables with the given name
				if (reportUndefinedVariables) {
					throw new CoreException(new Status(IStatus.ERROR, VariablesPlugin.getUniqueIdentifier(), VariablesPlugin.INTERNAL_ERROR, NLS.bind(VariablesMessages.StringSubstitutionEngine_3, new String[]{name}), null));
				}
				// leave as is
				return getOriginalVarText(var);
			}

			if (resolveVariables) {
				fSubs = true;
				return dynamicVariable.getValue(arg);
			}
			//leave as is
			return getOriginalVarText(var);
		}

		if (arg == null) {
			if (resolveVariables) {
				fSubs = true;
				return valueVariable.getValue();
			}
			//leave as is
			return getOriginalVarText(var);
		}
		// error - an argument specified for a value variable
		throw new CoreException(new Status(IStatus.ERROR, VariablesPlugin.getUniqueIdentifier(), VariablesPlugin.INTERNAL_ERROR, NLS.bind(VariablesMessages.StringSubstitutionEngine_4, new String[]{valueVariable.getName()}), null));
	}

	private String getOriginalVarText(VariableReference var) {
		StringBuilder res = new StringBuilder(var.getText());
		res.insert(0, VARIABLE_START);
		res.append(VARIABLE_END);
		return res.toString();
	}
}