commit c62300e78cc8a1c003f41653f34423a68db67449
author peter klausler <pklausler@nvidia.com> Thu Sep 30 15:58:38 2021 -0700
committer Copybara-Service <copybara-worker@google.com> Mon Oct 04 09:40:38 2021 -0700
tree 88c71b5079e58e2d19e5832b8d8b0b0adba576f2
parent a4757d8b1c156235b403eacbdb1efd371a49e2a7

[flang] Better error recovery for missing THEN in ELSE IF

The THEN keyword in the "ELSE IF (test) THEN" statement is useless
syntactically, and to omit it is a common error (at least for me!)
that has poor error recovery.  This patch changes the parser to
cough up a simple "expected 'THEN'" and still recognize the rest of
the IF construct.

Differential Revision: https://reviews.llvm.org/D110952

GitOrigin-RevId: 0061e681a3296ac9016891729e03e38ebb235bdc

lib/Evaluate/check-expression.cpp

diff --git a/lib/Evaluate/check-expression.cpp b/lib/Evaluate/check-expression.cpp
index cb910ca..2e0cc80 100644
--- a/lib/Evaluate/check-expression.cpp
+++ b/lib/Evaluate/check-expression.cpp
@@ -93,7 +93,7 @@
 }
 
 bool IsConstantExprHelper::operator()(const ProcedureRef &call) const {
-  // LBOUND, UBOUND, and SIZE with DIM= arguments will have been reritten
+  // LBOUND, UBOUND, and SIZE with DIM= arguments will have been rewritten
   // into DescriptorInquiry operations.
   if (const auto *intrinsic{std::get_if<SpecificIntrinsic>(&call.proc().u)}) {
     if (intrinsic->name == "kind" ||

lib/Parser/executable-parsers.cpp

diff --git a/lib/Parser/executable-parsers.cpp b/lib/Parser/executable-parsers.cpp
index a0b5cf2..66b217a 100644
--- a/lib/Parser/executable-parsers.cpp
+++ b/lib/Parser/executable-parsers.cpp
@@ -310,7 +310,7 @@
         many(construct<IfConstruct::ElseIfBlock>(
             unambiguousStatement(construct<ElseIfStmt>(
                 "ELSE IF" >> parenthesized(scalarLogicalExpr),
-                "THEN" >> maybe(name))),
+                recovery("THEN"_tok, ok) >> maybe(name))),
             block)),
         maybe(construct<IfConstruct::ElseBlock>(
             statement(construct<ElseStmt>("ELSE" >> maybe(name))), block)),

test/Parser/elseif-then.f90

diff --git a/test/Parser/elseif-then.f90 b/test/Parser/elseif-then.f90
new file mode 100644
index 0000000..29ec164
--- /dev/null
+++ b/test/Parser/elseif-then.f90
@@ -0,0 +1,8 @@
+! RUN: not %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+! CHECK-NOT: expected '=>'
+! CHECK: error: expected 'THEN'
+if (.false.) then
+else if (.false.)
+else
+end if
+end