PR11004: try / catch error-handling script syntax

* parse.h (try_block): New class.  Update basic visitors.
* staptree.cxx: Implement basic visitors.
* parse.cxx (expect_kw): Fix to actually look for keywords.
  (parse_try_block): New function.
  (lexer ctor): Designate 'try' and 'catch' as keywords.
* elaborate.cxx (dead_assignment_remover, dead_statmtexpr_remover): Optimize.
  (other visitors): Implement.
* translate.cxx (c_unparser): Implement via super-handy __local__ labels.
  (emit_probe, emit_function): Make outer out: label also __local__.
* testsuite/buildok/fortyone.stp, semko/fortynine.stp,
  systemtap.base/trycatch.exp: Test it.
* NEWS, doc/langref.txt, stap.1.in: Document it.

1 files changed, 10 insertions, 1 deletions

diff --git a/stap.1.in b/stap.1.in
index 6ef39ba5..531b0f88 100644
--- a/stap.1.in
+++ b/stap.1.in
@@ -493,7 +493,16 @@ not taken anywhere, then a return statement is not needed, and the
 function will have a special "unknown" type with no return value.
 .TP
 .BR next
-Return now from enclosing probe handler.
+Return now from enclosing probe handler.  This is especially useful in
+probe aliases that apply event filtering predicates.
+.TP
+.BR try " { STMT1 } " catch " { STMT2 }"
+Run the statements in the first block.  Upon any run-time errors, abort
+STMT1 and start executing STMT2.  Any errors in STMT2 will propagate to
+outer try/catch blocks, if any.
+.TP
+.BR try " { STMT1 } " catch "(VAR) { STMT2 }"
+Same as above, plus assign the error message to the string scalar variable VAR.
 .TP
 .BR delete " ARRAY[INDEX1, INDEX2, ...]"
 Remove from ARRAY the element specified by the index tuple.  The value will no