From 1c7a857ecbbc616a3e48dcbda717cc3072f554c0 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Sun, 6 May 2018 21:33:56 +0200
Subject: [PATCH] kernel: flush input line after early syntax error

Fixes a mild regression introduce by PR #1015, which in turn attempted
to fix parts of issue #995. With GAP 4.8 and also with this fix:

    gap> 1.2\3;
    Syntax error: Badly formed number
    1.2\3;
       ^

In GAP 4.9:

    gap> 1.2\3;
    Syntax error: Badly formed number
    1.2\3;
       ^
    3
---
 src/read.c                      |  3 +-
 tst/testinstall/kernel/read.tst | 66 +++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/src/read.c b/src/read.c
index dc237a8a35..c31f0dab4d 100644
--- a/src/read.c
+++ b/src/read.c
@@ -2713,8 +2713,9 @@ ExecStatus ReadEvalCommand(Obj context, Obj *evalResult, UInt *dualSemicolon)
     /* get the first symbol from the input                                 */
     Match( STATE(Symbol), "", 0UL );
 
-    /* using TRY_READ sets the jump buffer and mucks up the interpreter    */
+    // if scanning the first symbol produced a syntax error, abort
     if (STATE(NrError)) {
+        FlushRestOfInputLine();
         return STATUS_ERROR;
     }
 
diff --git a/tst/testinstall/kernel/read.tst b/tst/testinstall/kernel/read.tst
index 98a1c4b642..63a18482b8 100644
--- a/tst/testinstall/kernel/read.tst
+++ b/tst/testinstall/kernel/read.tst
@@ -64,5 +64,71 @@ Syntax error: Identifier expected in stream:1
 rec("a":=1);
       ^
 
+#
+# ReadEvalCommand
+#
+# See also https://github.com/gap-system/gap/issues/995
+#
+
+# some inputs which immediately trigger an error in ReadEvalCommand,
+# even before an interpreter has been started
+gap> '
+Syntax error: Character literal must not include <newline> in stream:1
+'
+^
+gap> 'x
+Syntax error: Missing single quote in character constant in stream:1
+'x
+ ^
+gap> "
+Syntax error: String must not include <newline> in stream:1
+"
+^
+gap> "x
+Syntax error: String must not include <newline> in stream:1
+"x
+ ^
+
+# similar inputs to the above, but here the error is triggered a bit
+# later, after the interpreter has already started
+gap> s := '
+Syntax error: Character literal must not include <newline> in stream:1
+s := '
+     ^
+Syntax error: ; expected in stream:2
+^
+gap> s := 'x
+Syntax error: Missing single quote in character constant in stream:1
+s := 'x
+      ^
+Syntax error: ; expected in stream:2
+^
+gap> s := "
+Syntax error: String must not include <newline> in stream:1
+s := "
+     ^
+Syntax error: ; expected in stream:2
+^
+gap> s := "x
+Syntax error: String must not include <newline> in stream:1
+s := "x
+      ^
+Syntax error: ; expected in stream:2
+^
+
+# errors in the middle of parsing a float literal
+gap> 12.34\56;
+Syntax error: Badly formed number in stream:1
+12.34\56;
+     ^
+gap> 12.34\a56;
+Syntax error: Badly formed number in stream:1
+12.34\a56;
+     ^
+gap> 12.34\56a;
+Syntax error: Badly formed number in stream:1
+12.34\56a;
+     ^
+
 #
 gap> STOP_TEST("kernel/read.tst", 1);