--- /dev/null
+# 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.
+
+# Explain failed assert to the console by modifying the AST.
+#
+# This module implements the service `AAssertExpr::explain_assert_str`,
+# which should be used by the engines.
+#
+# Example assert:
+#
+# ~~~nitish
+# var x = 0.0
+# var y = 1.0
+# assert x.is_approx(y, 0.5)
+# ~~~
+#
+# Produces the following output on failure:
+#
+# ~~~raw
+# Runtime assert: 0.0.is_approx(1.0, 0.5)
+# ~~~
+module explain_assert
+
+import astbuilder
+intrude import literal # for value=
+intrude import typing # for mtype=
+
+import explain_assert_api
+
+redef class ToolContext
+
+ # Phase modifying the AST to explain assets when they fail
+ var explain_assert_phase: Phase = new ExplainAssertPhase(self, [modelize_class_phase, typing_phase, literal_phase])
+end
+
+private class ExplainAssertPhase
+ super Phase
+
+ redef fun process_nmodule(nmodule)
+ do
+ var mmodule = nmodule.mmodule
+ if mmodule == null then return
+
+ # Skip if `mmodule` doesn't have access to `String`
+ var string_class = toolcontext.modelbuilder.try_get_mclass_by_name(nmodule, mmodule, "String")
+ if string_class == null then return
+
+ # Launch a visitor on all elements of the AST
+ var visitor = new ExplainAssertVisitor(toolcontext, mmodule, string_class.mclass_type)
+ visitor.enter_visit nmodule
+ end
+end
+
+# Visitor to find and explain asserts
+private class ExplainAssertVisitor
+ super Visitor
+
+ # The toolcontext is our entry point to most services
+ var toolcontext: ToolContext
+
+ # The visited module
+ var mmodule: MModule
+
+ # Type of `String` (the generated code does not work without a `String`)
+ var string_mtype: MType
+
+ # Tool to modify the AST
+ var builder = new ASTBuilder(mmodule) is lazy
+
+ redef fun visit(node)
+ do
+ # Recursively visit all sub-nodes
+ node.visit_all(self)
+
+ # Only work on asserts
+ if not node isa AAssertExpr then return
+ var expr = node.n_expr
+
+ # Skip assert on a single boolean var and asserts on false:
+ # ~~~
+ # assert false
+ # # or
+ # var x = false # Or any boolean expression
+ # assert x
+ # ~~~
+ if expr isa AVarExpr or expr isa AFalseExpr then return
+
+ # Build the superstring to explain the assert
+ var explain_str = new ASuperstringExpr
+
+ # Prepare attribute used by visited nodes
+ self.assert_node = node
+ self.explain_str = explain_str
+ expr.accept_explain_assert self
+
+ # Done! Store the superstring in the assert's node
+ if explain_str.n_exprs.not_empty then
+ node.explain_assert_str = explain_str
+ end
+ end
+
+ # Visited assert node
+ var assert_node: AAssertExpr is noinit
+
+ # Superstring in construction to explain the `assert_node`
+ var explain_str: ASuperstringExpr is noinit
+
+ # Build an `AStringExpr` containing `value`
+ #
+ # Add it to `explain_str` if `auto_add == true`, the default.
+ fun explain_string(value: String, auto_add: nullable Bool): AStringExpr
+ do
+ auto_add = auto_add or else true
+
+ var tk = new TString
+ tk.text = "\"{value}\""
+ var op = new AStringExpr
+ op.n_string = tk
+ op.mtype = string_mtype
+ op.value = value
+ op.location = assert_node.location
+
+ if auto_add then explain_str.n_exprs.add op
+ return op
+ end
+
+ # Add the value of `v_expr` to `explain_str` and protect null values
+ fun explain_expr(v_expr: AExpr)
+ do
+ var mtype = v_expr.mtype
+ if mtype == null then
+ explain_string "<unexpected error>"
+ return
+ end
+
+ # Set the expression value aside
+ var expr = v_expr.make_var_read
+
+ # Protect nullable types
+ if mtype isa MNullType then
+ explain_string "null"
+ return
+ else if mtype isa MNullableType then
+ var e = new AOrElseExpr
+ e.n_expr = expr
+ e.n_expr2 = explain_string("null", false)
+ e.location = assert_node.location
+ e.mtype = mmodule.object_type
+
+ explain_str.n_exprs.add e
+ return
+ end
+
+ explain_str.n_exprs.add expr
+ end
+
+ # Add all the arguments in `AExprs` to `explain_str`
+ fun explain_args(n_args: AExprs)
+ do
+ var first = true
+ for n_arg in n_args.to_a do
+ if not first then
+ explain_string ", "
+ else first = false
+
+ explain_expr n_arg
+ end
+ end
+end
+
+redef class AAssertExpr
+ redef var explain_assert_str = null
+end
+
+redef class AExpr
+ # Fill `v` to explain this node if the parent assert fails
+ private fun accept_explain_assert(v: ExplainAssertVisitor)
+ do if mtype != null then v.explain_expr self
+end
+
+redef class ABinopExpr
+ redef fun accept_explain_assert(v)
+ do
+ if n_expr.mtype == null or n_expr2.mtype == null then return
+
+ v.explain_expr n_expr
+ v.explain_string " {n_op.text} "
+ v.explain_expr n_expr2
+ end
+end
+
+redef class ACallExpr
+ redef fun accept_explain_assert(v)
+ do
+ if n_expr.mtype == null then return
+
+ v.explain_expr n_expr
+ v.explain_string ".{n_qid.n_id.text}"
+
+ if n_args.to_a.not_empty then
+ v.explain_string "("
+ v.explain_args n_args
+ v.explain_string ")"
+ end
+ end
+end
+
+redef class ABraExpr
+ redef fun accept_explain_assert(v)
+ do
+ if n_expr.mtype == null then return
+
+ v.explain_expr n_expr
+ v.explain_string "["
+ v.explain_args n_args
+ v.explain_string "]"
+ end
+end
+
+redef class AIsaExpr
+ redef fun accept_explain_assert(v)
+ do
+ if n_expr.mtype == null then return
+
+ v.explain_expr n_expr
+ v.explain_string " {n_kwisa.text} "
+ v.explain_string n_type.collect_text
+ end
+end
+
+redef class ANotExpr
+ redef fun accept_explain_assert(v)
+ do
+ v.explain_string "{n_kwnot.text} "
+ n_expr.accept_explain_assert v
+ end
+end
+
+redef class ABinBoolExpr
+ # Don't explain the conditions using `and`, `or`, etc.
+ redef fun accept_explain_assert(v) do end
+end
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