print legend for the output

Summary:
F for files, . for procedures, and a few more for developer mode.

Also add the crash message to the crash symbol, because if infer crashes we
want as much information as possible.

```
$ infer -- javac Hello.java
Starting analysis (Infer version v0.8.1-8e8c6fa)

legend:
  "F" analyzing a file
  "." analyzing a procedure

F..

Analyzed 1 file

Found 1 issue

Hello.java:13: error: NULL_DEREFERENCE
  object s last assigned on line 12 could be null and is dereferenced at line 13
  11.     int test() {
  12.       String s = null;
  13. >     return s.length();
  14.     }
  15.   }
  16.

Summary of the reports

  NULL_DEREFERENCE: 1
$ infer -g -- javac Hello.java
...
Starting analysis (Infer version v0.8.1-8e8c6fa)

legend:
  "F" analyzing a file
  "." analyzing a procedure
  "C" analyzer crashed
  "T" timeout: procedure analysis took too much time
  "S" timeout: procedure analysis took too many symbolic execution steps
  "R" timeout: procedure analysis took too many recursive iterations

...
```

Reviewed By: sblackshear

Differential Revision: D3288081

fbshipit-source-id: becea34

infer/src/backend/config.ml

@@ -147,6 +147,14 @@ let unsafe_unret = "<\"Unsafe_unretained\">"
 
 let weak = "<\"Weak\">"
 
+(** letters used in the analysis output *)
+let log_analysis_file = "F"
+let log_analysis_procedure = "."
+let log_analysis_wallclock_timeout = "T"
+let log_analysis_symops_timeout = "S"
+let log_analysis_recursion_timeout = "R"
+let log_analysis_crash = "C"
+
 
 (** Compile time configuration values *)
 

infer/src/backend/config.mli

@@ -50,6 +50,12 @@ val incremental_procs : bool
 val inferconfig_file : string
 val initial_analysis_time : float
 val ivar_attributes : string
+val log_analysis_file : string
+val log_analysis_procedure : string
+val log_analysis_wallclock_timeout : string
+val log_analysis_symops_timeout : string
+val log_analysis_recursion_timeout : string
+val log_analysis_crash : string
 val max_recursion : int
 val meet_level : int
 val models_dir : string

infer/src/backend/inferanalyze.ml

@@ -123,7 +123,21 @@ let output_json_makefile_stats clusters =
 let print_prolog () =
   match Config.cluster_cmdline with
   | None ->
-      L.stdout "Starting analysis (Infer version %s)@." Version.versionString;
+      L.stdout "Starting analysis (Infer version %s)@\n" Version.versionString;
+      L.stdout "@\n";
+      L.stdout "legend:@\n";
+      L.stdout "  \"%s\" analyzing a file@\n" Config.log_analysis_file;
+      L.stdout "  \"%s\" analyzing a procedure@\n" Config.log_analysis_procedure;
+      if Config.developer_mode then (
+        L.stdout "  \"%s\" analyzer crashed@\n" Config.log_analysis_crash;
+        L.stdout "  \"%s\" timeout: procedure analysis took too much time@\n"
+          Config.log_analysis_wallclock_timeout;
+        L.stdout "  \"%s\" timeout: procedure analysis took too many symbolic execution steps@\n"
+          Config.log_analysis_symops_timeout;
+        L.stdout "  \"%s\" timeout: procedure analysis took too many recursive iterations@\n"
+          Config.log_analysis_recursion_timeout;
+      );
+      L.stdout "@\n@?";
   | Some clname -> L.stdout "Cluster %s@." clname
 
 let process_cluster_cmdline fname =

infer/src/backend/logging.ml

@@ -201,21 +201,21 @@ let log_progress_simple text =
     F.fprintf Format.err_formatter "%s@?" text
 
 let log_progress_file () =
-  log_progress_simple "F"
+  log_progress_simple Config.log_analysis_file
 
 let log_progress_procedure () =
-  log_progress_simple "."
+  log_progress_simple Config.log_analysis_procedure
 
 let log_progress_timeout_event failure_kind =
   if Config.developer_mode then
     begin
       match failure_kind with
       | SymOp.FKtimeout ->
-          log_progress_simple "T"
+          log_progress_simple Config.log_analysis_wallclock_timeout
       | SymOp.FKsymops_timeout _ ->
-          log_progress_simple "S"
+          log_progress_simple Config.log_analysis_symops_timeout
       | SymOp.FKrecursion_timeout _ ->
-          log_progress_simple "R"
-      | SymOp.FKcrash _ ->
-          log_progress_simple "C"
+          log_progress_simple Config.log_analysis_recursion_timeout
+      | SymOp.FKcrash msg ->
+          log_progress_simple (Printf.sprintf "%s(%s)" Config.log_analysis_crash msg)
     end