In the analysis server API, change RequestError.code to an enum.

pkg/analysis_server/tool/spec/spec_input.html

Index: pkg/analysis_server/tool/spec/spec_input.html
diff --git a/pkg/analysis_server/tool/spec/spec_input.html b/pkg/analysis_server/tool/spec/spec_input.html
index 3d0f0746aaa74126eed3ab399ab62bcc5c3d038f..28aebb156a3b54350fc44787ca166463df68e1a0 100644
--- a/pkg/analysis_server/tool/spec/spec_input.html
+++ b/pkg/analysis_server/tool/spec/spec_input.html
@@ -1879,12 +1879,11 @@
       <type name="Error">
         <p>
           An indication of a problem with the execution of the server,
-          typically in response to a request. The error codes that can
-          be returned are documented in the section titled Errors.
+          typically in response to a request.
         </p>
         <object>
           <field name="code">
-            <ref>String</ref>
+            <ref>RequestErrorCode</ref>
             <p>
               A code that uniquely identifies the error that occurred.
             </p>
@@ -2572,6 +2571,66 @@
           <field name="type" value="remove"><ref>String</ref></field>
         </object>
       </type>
+      <type name="RequestErrorCode">
+        <p>
+          An enumeration of the types of errors that can occur in the
+          execution of the server.
+        </p>
+        <enum>
+          <value>
+            <code>GET_ERRORS_ERROR</code>

[Brian Wilkerson, 2014/08/27 21:05:22]

This seems rather vague. Any chance we can be more specific about the nature of
the error? If not, then perhaps something more general to make it clear that we
can't be specific, such as REQUEST_ERROR.

[Paul Berry, 2014/08/29 07:30:21]

Agreed.  I've added a TODO comment.

+            <p>
+              An error occurred during the processing of an
+              "analysis.getErrors" request.
+            </p>
+          </value>
+          <value>
+            <code>INVALID_PARAMETER</code>
+            <p>
+              One of the method parameters was invalid.
+            </p>
+          </value>
+          <value>
+            <code>INVALID_REQUEST</code>
+            <p>
+              A malformed request was received.
+            </p>
+          </value>
+          <value>
+            <code>SERVER_ALREADY_STARTED</code>

[Brian Wilkerson, 2014/08/27 21:05:21]

Are you planning on removing this and the following value in a later CL?

[Paul Berry, 2014/08/29 07:30:21]

Yes.

+            <!-- TODO(paulberry): this error code doesn't make sense
+                 anymore. -->
+            <p>
+              The analysis server has already been started (and hence
+              won't accept new connections).
+            </p>
+          </value>
+          <value>
+            <code>UNANALYZED_PRIORITY_FILES</code>
+            <!-- TODO(paulberry): this error shouldn't be issued under
+                 our new "eventual consistency" model. -->
+            <p>
+              An "analysis.setPriorityFiles" request includes one or
+              more files that are not being analyzed.
+            </p>
+          </value>
+          <value>
+            <code>UNKNOWN_REQUEST</code>
+            <p>
+              A request was received which the analysis server does
+              not recognize, or cannot handle in its current
+              configuation.
+            </p>
+          </value>
+          <value>
+            <code>UNSUPPORTED_FEATURE</code>

[Brian Wilkerson, 2014/08/27 21:05:21]

Not clear to me how this differs from UNKNOWN_REQUEST, probably because I don't
know what "feature" means in this context.

[Paul Berry, 2014/08/29 07:30:21]

I don't know either.  I've added a TODO comment to remind us to clean this up.

+            <p>
+              The analysis server was requested to perform an action
+              which is not supported.
+            </p>
+          </value>
+        </enum>
+      </type>
       <type name="SearchId">
         <ref>String</ref>
         <p>