typing: new warning `useless-truism` to catch trainees.

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/src/semantize/typing.nit b/src/semantize/typing.nit
index 8890ba9..3297d12 100644 (file)
--- a/src/semantize/typing.nit
+++ b/src/semantize/typing.nit
@@ -2017,6 +2017,10 @@ redef class AEqFormExpr
 
                if mtype == null or mtype2 == null then return
 
+               if mtype == v.type_bool(self) and (n_expr2 isa AFalseExpr or n_expr2 isa ATrueExpr) then
+                       v.modelbuilder.warning(self, "useless-truism", "Warning: useless comparison to a Bool literal.")
+               end
+
                if not mtype2 isa MNullType then return
 
                v.check_can_be_null(n_expr, mtype)

diff --git a/tests/sav/warn_truism.res b/tests/sav/warn_truism.res
new file mode 100644 (file)
index 0000000..7b485c1
--- /dev/null
+++ b/tests/sav/warn_truism.res
@@ -0,0 +1,4 @@
+warn_truism.nit:18,4--12: Warning: useless comparison to a Bool literal.
+warn_truism.nit:19,9--18: Warning: useless comparison to a Bool literal.
+warn_truism.nit:20,10--26: Warning: useless comparison to a Bool literal.
+warn_truism.nit:20,33--41: Warning: useless comparison to a Bool literal.

diff --git a/tests/warn_truism.nit b/tests/warn_truism.nit
new file mode 100644 (file)
index 0000000..32e1e1d
--- /dev/null
+++ b/tests/warn_truism.nit
@@ -0,0 +1,29 @@
+# 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
+
+var a = true
+if a == true then end
+var b = a != false
+var c = ((a or b) == false) and b != true
+
+# only warn the common case (not those)
+if true == a then end
+if a == (true) then end
+
+# dont warn if operand 1 is not a bool
+var o: nullable Bool = a
+if o == true then end
+if o or else false then end