From 958d841c57fd96b2dec9b61158f4da2eca6c9d7f Mon Sep 17 00:00:00 2001
From: Jean Privat <jean@pryen.org>
Date: Thu, 25 Feb 2016 14:11:57 -0500
Subject: [PATCH] typing: include a hook to enable more precise error
 information on 'expected expression' errors

Signed-off-by: Jean Privat <jean@pryen.org>
---
 src/semantize/typing.nit          |   20 ++++++++++++++++++-
 tests/error_arg.nit               |   39 +++++++++++++++++++++++++++++++++++++
 tests/sav/base_meth_call_alt1.res |    2 +-
 tests/sav/error_arg.res           |    9 +++++++++
 tests/sav/error_arg_alt1.res      |    2 ++
 5 files changed, 70 insertions(+), 2 deletions(-)
 create mode 100644 tests/error_arg.nit
 create mode 100644 tests/sav/error_arg.res
 create mode 100644 tests/sav/error_arg_alt1.res

diff --git a/src/semantize/typing.nit b/src/semantize/typing.nit
index aeb3b7e..ddc87e2 100644
--- a/src/semantize/typing.nit
+++ b/src/semantize/typing.nit
@@ -152,7 +152,11 @@ private class TypeVisitor
 			end
 			return null # forward error
 		end
-		self.error(nexpr, "Error: expected an expression.")
+		var more_message = null
+		var p = nexpr.parent
+		if p != null then more_message = p.bad_expr_message(nexpr)
+		if more_message == null then more_message = "" else more_message = " " + more_message
+		self.error(nexpr, "Error: expected an expression{more_message}.")
 		return null
 	end
 
@@ -802,6 +806,12 @@ end
 
 redef class ANode
 	private fun accept_post_typing(v: TypeVisitor) do end
+
+	# An additional information message to explain the role of a child expression.
+	#
+	# The point of the method is to allow some kind of double dispatch so the parent
+	# choose how to describe its children.
+	private fun bad_expr_message(child: AExpr): nullable String do return null
 end
 
 redef class AAttrPropdef
@@ -1710,6 +1720,14 @@ redef class ASendExpr
 	# The property invoked by the send.
 	var callsite: nullable CallSite
 
+	redef fun bad_expr_message(child)
+	do
+		if child == self.n_expr then
+			return "to be the receiver of `{self.property_name}`"
+		end
+		return null
+	end
+
 	redef fun accept_typing(v)
 	do
 		var nrecv = self.n_expr
diff --git a/tests/error_arg.nit b/tests/error_arg.nit
new file mode 100644
index 0000000..c550d9f
--- /dev/null
+++ b/tests/error_arg.nit
@@ -0,0 +1,39 @@
+# This file is part of NIT ( http://www.nitlanguage.org ).
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import core::kernel
+
+redef class Int
+	fun a: Int do return 10*self+self.abs
+end
+
+fun foo(a: Int): Int do
+	a.output
+	return a
+end
+fun bar(a: Int) do a.output
+
+foo 1.a
+foo(1.a)
+foo (1).a
+foo(1).a
+foo((1).a)
+
+'\n'.output
+
+bar 1.a
+bar(1.a)
+#alt1#bar (1).a
+#alt1#bar(1).a
+bar((1).a)
diff --git a/tests/sav/base_meth_call_alt1.res b/tests/sav/base_meth_call_alt1.res
index 5b14b4e..b2c999e 100644
--- a/tests/sav/base_meth_call_alt1.res
+++ b/tests/sav/base_meth_call_alt1.res
@@ -1 +1 @@
-alt/base_meth_call_alt1.nit:36,1--6: Error: expected an expression.
+alt/base_meth_call_alt1.nit:36,1--6: Error: expected an expression to be the receiver of `output`.
diff --git a/tests/sav/error_arg.res b/tests/sav/error_arg.res
new file mode 100644
index 0000000..1aa7d08
--- /dev/null
+++ b/tests/sav/error_arg.res
@@ -0,0 +1,9 @@
+11
+11
+1
+1
+11
+
+11
+11
+11
diff --git a/tests/sav/error_arg_alt1.res b/tests/sav/error_arg_alt1.res
new file mode 100644
index 0000000..efe82e4
--- /dev/null
+++ b/tests/sav/error_arg_alt1.res
@@ -0,0 +1,2 @@
+alt/error_arg_alt1.nit:37,1--7: Error: expected an expression to be the receiver of `a`.
+alt/error_arg_alt1.nit:38,1--6: Error: expected an expression to be the receiver of `a`.
-- 
1.7.9.5