ErrorHandlingVisitor


1   package polyglot.visit;
2   
3   import polyglot.ast.*;
4   import polyglot.types.*;
5   import polyglot.util.*;
6   import polyglot.frontend.Job;
7   import polyglot.main.Report;
8   import java.util.*;
9   
10  /**
11   */
12  public class ErrorHandlingVisitor extends HaltingVisitor
13  {
14      protected boolean error;
15      protected Job job;
16      protected TypeSystem ts;
17      protected NodeFactory nf;
18  
19      public ErrorHandlingVisitor(Job job, TypeSystem ts, NodeFactory nf) {
20          this.job = job;
21          this.ts = ts;
22          this.nf = nf;
23      }
24  
25      /** Returns the <code>Job</code> that this Visitor is part of.
26       *
27       * @see polyglot.frontend.Job
28       */
29      public Job job() {
30          return job;
31      }
32  
33      /**
34       * Part of the initialization done by begin() in an ErrorHandlingVisitor
35       * method is initializing the error-handling state.
36       */
37      public NodeVisitor begin() {
38          this.error = false;
39          return super.begin();
40      }
41  
42      /** Returns the <code>ErrorQueue</code> for the current Job.
43       *
44       * @see polyglot.util.ErrorQueue
45       */
46      public ErrorQueue errorQueue() {
47          return job.compiler().errorQueue();
48      }
49  
50      /** Returns the <code>NodeFactory</code> that this Visitor is using.
51       *
52       * @see polyglot.ast.NodeFactory
53       */
54      public NodeFactory nodeFactory() {
55          return nf;
56      }
57  
58      /** Returns the <code>TypeSystem</code> that this Visitor is using.
59       *
60       * @see polyglot.types.TypeSystem
61       */
62      public TypeSystem typeSystem() {
63          return ts;
64      }
65  
66      /** Replaces the functionality of the <code>enter()</code> method; all 
67        * sub-classes should over-ride this method instead of 
68        * <code>enter()</code> if there is any chance of exceptions being
69        * generated.
70        *
71        * This method is the replacement for the <code>enter()</code> method, 
72        * so that all of its subclasses gain the error handling capabilities 
73        * of this visitor without having to rewrite it for the 
74        * <code>enter()</code> for each sub-class.
75        *
76        * This method allows for a <code>SemanticException</code> to be 
77        * thrown in the body, while <code>enter()</code> does not.
78        * 
79        * @see polyglot.visit.NodeVisitor#enter(Node, Node)
80        * @throws SemanticException
81        * @param n The root of the subtree to be traversed.
82        * @return The <code>ErrorHandlingVisitor</code> which should be 
83        * used to visit the children of <code>n</code>.
84       */
85      protected NodeVisitor enterCall(Node parent, Node n)
86                  throws SemanticException {
87          if (Report.should_report(Report.visit, 3))
88          Report.report(3, "enter: " + parent + " -> " + n);
89          return enterCall(n);
90      }
91  
92      protected NodeVisitor enterCall(Node n) throws SemanticException {
93          return this;
94      }
95  
96      /** This method determines what should be returned by <code>enter()</code>
97        * should its call to <code>enterCall()</code> throw a
98        * <code>SemanticException</code>.
99        *
100       * @param n The root of the subtree that was traversed.
101       * @return The <code>ErrorHandlingVisitor</code> which should be
102       * used to visit the childre of <code>n</code>.
103       */
104     protected NodeVisitor enterError(Node n) {
105     return this;
106     }
107 
108     /** Contains all of the functionality that can be done in the <code> leave
109       * </code> method, but allows <code>SemanticExceptions</code> to be
110       * thrown.
111       *
112       * This method is in addition to the <code>leave</code> method, 
113       * and allows the compiler writer to write code that can throw errors
114       * and let the polyglot infrastructure handle the exceptions.
115       *
116       * @see polyglot.visit.NodeVisitor#leave(Node, Node, NodeVisitor)
117       * @throws SemanticException
118       * @param old The original state of root of the current subtree.
119       * @param n The current state of the root of the current subtree.
120       * @param v The <code>NodeVisitor</code> object used to visit the children.
121       * @return The final result of the traversal of the tree rooted at
122       * <code>n</code>.
123       */
124     protected Node leaveCall(Node old, Node n, NodeVisitor v)
125         throws SemanticException {
126 
127     return leaveCall(n);
128     }
129 
130     protected Node leaveCall(Node n) throws SemanticException {
131     return n;
132     }
133 
134     /** Return true if we should catch errors thrown when visiting the node. */
135     protected boolean catchErrors(Node n) {
136     return n instanceof Stmt
137         || n instanceof ClassMember
138         || n instanceof ClassDecl
139         || n instanceof Import
140         || n instanceof SourceFile;
141     }
142 
143     /**
144      * Begin normal traversal of a subtree rooted at <code>n</code>. This gives
145      * the visitor the option of changing internal state or returning a new
146      * visitor which will be used to visit the children of <code>n</code>.
147      *
148      * This method delegates all responsibility of functionality to the
149      * <code>enterCall</code> method, and handles and reports any exceptions
150      * generated by <code>enterCall</code>.
151      *
152      * In overriding this method, unless the class explicitly does not
153      * want to maintain any of the error handling aspects of this class, a call
154      * <code>super.enter</code> should be embedded within the method at the 
155      * end.
156      *
157      * @param n The root of the subtree to be traversed.
158      * @return The <code>NodeVisitor</code> which should be used to visit the
159      * children of <code>n</code>.
160      */
161     public NodeVisitor enter(Node parent, Node n) {
162         if (Report.should_report(Report.visit, 5))
163         Report.report(5, "enter(" + n + ")");
164 
165         if (catchErrors(n)) {
166             this.error = false;
167         }
168 
169         try {
170             // should copy the visitor
171             return (ErrorHandlingVisitor) enterCall(parent, n);
172         }
173     catch (SemanticException e) {
174             if (e.getMessage() != null) {
175                 Position position = e.position();
176 
177                 if (position == null) {
178                     position = n.position();
179                 }
180 
181                 errorQueue().enqueue(ErrorInfo.SEMANTIC_ERROR,
182                                     e.getMessage(), position);
183             }
184             else {
185                 // silent error; these should be thrown only
186                 // when the error has already been reported 
187             }
188 
189             if (! catchErrors(n)) {
190                 this.error = true;
191             }
192 
193         return enterError(n);
194         }
195     }
196 
197 
198     /**
199      * This method is called after all of the children of <code>n</code>
200      * have been visited. In this case, these children were visited by the
201      * visitor <code>v</code>. This is the last chance for the visitor to
202      * modify the tree rooted at <code>n</code>. This method will be called
203      * exactly the same number of times as <code>entry</code> is called.
204      * That is, for each node that is not overriden, <code>enter</code> and
205      * <code>leave</code> are each called exactly once.
206      * <p>
207      * Note that if <code>old == n</code> then the vistior should make a copy
208      * of <code>n</code> before modifying it. It should then return the
209      * modified copy.
210      *
211      * This method delegates all responsibility of functionality to the
212      * <code>leaveCall</code> method, and handles and reports any exceptions
213      * generated by <code> leaveCall</code>.
214      *
215      * In overriding this method, unless the class explicitly does not
216      * want to maintain any of the error handling aspects of this class, a call
217      * <code>super.leave</code> should be embedded within the method at the 
218      * end.
219      *
220      * @param old The original state of root of the current subtree.
221      * @param n The current state of the root of the current subtree.
222      * @param v The <code>NodeVisitor</code> object used to visit the children.
223      * @return The final result of the traversal of the tree rooted at
224      * <code>n</code>.
225      */
226  
227     public Node leave(Node parent, Node old, Node n, NodeVisitor v) {
228         try {
229             if (v instanceof ErrorHandlingVisitor &&
230                 ((ErrorHandlingVisitor) v).error) {
231 
232                 if (Report.should_report(Report.visit, 5))
233             Report.report(5, "leave(" + n + "): error below");
234 
235                 if (catchErrors(n)) {
236                     this.error = false;
237                     ((ErrorHandlingVisitor) v).error = false;
238                 }
239                 else {
240                     // propagate the error outward
241                     this.error = true;
242                 }
243 
244                 // don't visit the node
245                 return n;
246             }
247 
248             if (Report.should_report(Report.visit, 5))
249         Report.report(5, "leave(" + n + "): calling leaveCall");
250 
251             return leaveCall(old, n, v);
252     }
253     catch (SemanticException e) {
254             if (e.getMessage() != null) {
255                 Position position = e.position();
256 
257                 if (position == null) {
258                     position = n.position();
259                 }
260 
261                 errorQueue().enqueue(ErrorInfo.SEMANTIC_ERROR,
262                                     e.getMessage(), position);
263             }
264             else {
265                 // silent error; these should be thrown only
266                 // when the error has already been reported 
267             }
268 
269             if (catchErrors(n)) {
270                 this.error = false;
271                 ((ErrorHandlingVisitor) v).error = false;
272             }
273             else {
274                 this.error = true;
275                 ((ErrorHandlingVisitor) v).error = true;
276             }
277 
278             return n;
279         }
280     }
281 }
282 
283
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