Compiler: improve error message of a failing as to include the orig…

…inal type as well as the filename and line number. Fixes #2663

spec/compiler/codegen/cast_spec.cr

@@ -48,7 +48,7 @@ describe "Code gen: cast" do
         a as Char
         false
       rescue ex
-        (ex.message == "cast to Char failed") && (ex.class == TypeCastError)
+        ex.message.not_nil!.includes?("cast from Int32 to Char failed") && (ex.class == TypeCastError)
       end
       )).to_b.should be_true
   end
@@ -72,7 +72,7 @@ describe "Code gen: cast" do
         a as Float64 | Char
         false
       rescue ex
-        (ex.message == "cast to (Char | Float64) failed") && (ex.class == TypeCastError)
+        ex.message.not_nil!.includes?("cast from Int32 to (Char | Float64) failed") && (ex.class == TypeCastError)
       end
       )).to_b.should be_true
   end
@@ -120,7 +120,7 @@ describe "Code gen: cast" do
         a as CastSpecBaz
         false
       rescue ex
-        (ex.message == "cast to CastSpecBaz failed") && (ex.class == TypeCastError)
+        ex.message.not_nil!.includes?("cast from CastSpecBar to CastSpecBaz failed") && (ex.class == TypeCastError)
       end
       )).to_b.should be_true
   end
@@ -187,7 +187,7 @@ describe "Code gen: cast" do
         a as Nil
         false
       rescue ex
-        (ex.message.not_nil!.includes? "cast to Nil failed") && (ex.class == TypeCastError)
+        ex.message.not_nil!.includes?("cast from Reference to Nil failed") && (ex.class == TypeCastError)
       end
       )).to_b.should be_true
   end

src/compiler/crystal/codegen/codegen.cr

@@ -1076,7 +1076,11 @@ module Crystal
           cond cmp, matches_block, doesnt_match_block
 
           position_at_end doesnt_match_block
-          accept type_cast_exception_call(to_type)
+
+          temp_var_name = @mod.new_temp_var_name
+          context.vars[temp_var_name] = LLVMVar.new(last_value, obj_type, already_loaded: true)
+          accept type_cast_exception_call(obj_type, to_type, node, temp_var_name)
+          context.vars.delete temp_var_name
 
           position_at_end matches_block
           @last = downcast last_value, resulting_type, obj_type, true
@@ -1126,11 +1130,25 @@ module Crystal
       false
     end
 
-    def type_cast_exception_call(to_type)
-      ex = Call.new(Path.global("TypeCastError"), "new", StringLiteral.new("cast to #{to_type} failed"))
+    def type_cast_exception_call(from_type, to_type, node, var_name)
+      pieces = [
+        StringLiteral.new("cast from "),
+        Call.new(Var.new(var_name), "class"),
+        StringLiteral.new(" to #{to_type} failed"),
+      ] of ASTNode
+
+      if location = node.location
+        pieces << StringLiteral.new (", at #{location.filename}:#{location.line_number}")
+      end
+
+      ex = Call.new(Path.global("TypeCastError"), "new", StringInterpolation.new(pieces))
       call = Call.global("raise", ex)
+      call = @mod.normalize(call)
 
-      @mod.visit_main call
+      meta_vars = MetaVars.new
+      meta_vars[var_name] = MetaVar.new(var_name, type: from_type)
+      visitor = MainVisitor.new(@mod, meta_vars)
+      @mod.visit_main call, visitor: visitor
       call
     end
 

src/compiler/crystal/semantic/main_visitor.cr

@@ -2,8 +2,8 @@ require "./base_type_visitor"
 
 module Crystal
   class Program
-    def visit_main(node)
-      node.accept MainVisitor.new(self)
+    def visit_main(node, visitor = MainVisitor.new(self))
+      node.accept visitor
 
       fix_empty_types node
       node = cleanup node