Fix to #225, added better error reporting for internal compiler errors.

pallene/ast.lua

@@ -100,7 +100,7 @@ function ast.toplevel_names(tl_node)
     elseif tag == "ast.Toplevel.Builtin" then
         table.insert(names, tl_node.name)
     else
-        error("impossible")
+        typedecl.tag_error(tag)
     end
     return names
 end

pallene/checker.lua

@@ -124,7 +124,7 @@ declare_type("Name", {
 })
 
 function Checker:add_type(name, typ)
-    assert(string.match(typ._tag, "^types%.T%."))
+    assert(typedecl.match_tag(typ._tag, "types.T"))
     self.symbol_table:add_symbol(name, checker.Name.Type(typ))
 end
 
@@ -218,7 +218,7 @@ function Checker:from_ast_type(ast_typ)
         return types.T.Function(p_types, ret_types)
 
     else
-        error("impossible")
+        typedecl.tag_error(tag)
     end
 end
 
@@ -360,7 +360,7 @@ function Checker:check_program(prog_ast)
                     self:add_type(tl_node.name, typ)
 
                 else
-                    error("impossible")
+                    typedecl.tag_error(tag)
                 end
             end
 
@@ -455,7 +455,7 @@ function Checker:check_stat(stat)
             elseif loop_type._tag == "types.T.Float" then
                 stat.step = ast.Exp.Float(stat.limit.loc, 1.0)
             else
-                error("impossible")
+                typedecl.tag_error(loop_type._tag, "loop type is not a number.")
             end
         end
 
@@ -515,7 +515,7 @@ function Checker:check_stat(stat)
         -- ok
 
     else
-        error("impossible")
+        typedecl.tag_error(tag)
     end
 
     return stat
@@ -547,7 +547,7 @@ function Checker:check_var(var)
                 "cannot reference module name '%s' without dot notation",
                 var.name)
         else
-            error("impossible")
+            typedecl.tag_error(cname._tag)
         end
 
     elseif tag == "ast.Var.Dot" then
@@ -603,7 +603,7 @@ function Checker:check_var(var)
         var._type = arr_type.elem
 
     else
-        error("impossible")
+        typedecl.tag_error(tag)
     end
     return var
 end
@@ -618,8 +618,10 @@ function Checker:coerce_numeric_exp_to_float(exp)
         return exp
     elseif tag == "types.T.Integer" then
         return self:check_exp_synthesize(ast.Exp.ToFloat(exp.loc, exp))
+    elseif typedecl.match_tag(tag, "types.T") then
+        typedecl.tag_error(tag, "this type cannot be coerced to float.")
     else
-        error("impossible")
+        typedecl.tag_error(tag)
     end
 end
 
@@ -687,7 +689,7 @@ function Checker:check_exp_synthesize(exp)
             check_type_is_condition(exp.exp, "'not' operator")
             exp._type = types.T.Boolean()
         else
-            error("impossible")
+            typedecl.tag_error(op)
         end
 
     elseif tag == "ast.Exp.Binop" then
@@ -797,7 +799,7 @@ function Checker:check_exp_synthesize(exp)
             exp._type = types.T.Integer()
 
         else
-            error("impossible")
+            typedecl.tag_error(op)
         end
 
     elseif tag == "ast.Exp.CallFunc" then
@@ -865,7 +867,7 @@ function Checker:check_exp_synthesize(exp)
         exp._type = types.T.Float()
 
     else
-        error("impossible")
+        typedecl.tag_error(tag)
     end
 
     return exp
@@ -898,7 +900,7 @@ function Checker:check_exp_verify(exp, expected_type, errmsg_fmt, ...)
                         field.exp, expected_type.elem,
                         "array initializer")
                 else
-                    error("impossible")
+                    typedecl.tag_error(ftag)
                 end
             end
 
@@ -928,7 +930,7 @@ function Checker:check_exp_verify(exp, expected_type, errmsg_fmt, ...)
                         field.exp, field_type,
                         "table initializer")
                 else
-                    error("impossible")
+                    typedecl.tag_error(ftag)
                 end
             end
 

pallene/coder.lua

@@ -39,7 +39,7 @@ local function ctype(typ)
     elseif tag == "types.T.Table"    then return "Table *"
     elseif tag == "types.T.Record"   then return "Udata *"
     elseif tag == "types.T.Any"      then return "TValue"
-    else error("impossible")
+    else   typedecl.tag_error(tag)
     end
 end
 
@@ -90,7 +90,7 @@ local function lua_value(typ, src_slot)
     elseif tag == "types.T.Table"    then tmpl = "hvalue($src)"
     elseif tag == "types.T.Record"   then tmpl = "uvalue($src)"
     elseif tag == "types.T.Any"      then tmpl = "*($src)"
-    else error("impossible")
+    else typedecl.tag_error(tag)
     end
     return (util.render(tmpl, {src = src_slot}))
 end
@@ -117,8 +117,9 @@ local function set_stack_slot(typ, dst_slot, value)
     elseif tag == "types.T.Table"    then tmpl = "sethvalue(L, $dst, $src);"
     elseif tag == "types.T.Record"   then tmpl = "setuvalue(L, $dst, $src);"
     elseif tag == "types.T.Any"      then tmpl = "setobj(L, $dst, &$src);"
-    else error("impossible")
+    else typedecl.tag_error(tag)
     end
+
     return (util.render(tmpl, { dst = dst_slot, src = value }))
 end
 
@@ -165,8 +166,8 @@ local function pallene_type_tag(typ)
     elseif tag == "types.T.Array"    then return "LUA_TTABLE"
     elseif tag == "types.T.Table"    then return "LUA_TTABLE"
     elseif tag == "types.T.Record"   then return "LUA_TUSERDATA"
-    elseif tag == "types.T.Any"    then error("value is not a tag")
-    else error("impossible")
+    elseif tag == "types.T.Any"      then typedecl.tag_error(tag, "'Any' is not a Lua type tag.")
+    else typedecl.tag_error(tag)
     end
 end
 
@@ -324,8 +325,10 @@ function Coder:c_value(value)
         local f_id = value.id
         local typ = self.module.functions[f_id].typ
         return lua_value(typ, self:function_upvalue_slot(f_id))
+    elseif typedecl.match_tag(tag, "ir.Value") then
+        typedecl.tag_error(tag, "unable to get C expression for this value type.")
     else
-        error("impossible")
+        typedecl.tag_error(tag)
     end
 end
 
@@ -1476,7 +1479,7 @@ gen_cmd["For"] = function(self, cmd, func)
     elseif typ._tag == "types.T.Float" then
         macro = "PALLENE_FLT_FOR_LOOP"
     else
-        error("impossible")
+        typedecl.tag_error(typ._tag)
     end
 
     return (util.render([[
@@ -1502,7 +1505,7 @@ gen_cmd["CheckGC"] = function(self, cmd, func)
 end
 
 function Coder:generate_cmd(func, cmd)
-    local name = assert(string.match(cmd._tag, "^ir%.Cmd%.(.*)$"))
+    local name = assert(typedecl.match_tag(cmd._tag, "ir.Cmd"))
     local f = assert(gen_cmd[name], "impossible")
     local out = f(self, cmd, func)
 
@@ -1601,7 +1604,7 @@ function Coder:generate_luaopen_function()
                     ix = C.integer(self.upvalue_of_function[upv.f_id]),
                 }))
             else
-                error("impossible")
+                typedecl.tag_error(tag)
             end
 
             table.insert(init_constants, util.render([[

pallene/constant_propagation.lua

@@ -4,6 +4,7 @@
 -- SPDX-License-Identifier: MIT
 
 local ir = require "pallene.ir"
+local typedecl = require "pallene.typedecl"
 
 local constant_propagation = {}
 
@@ -17,7 +18,7 @@ local function is_constant_value(v)
     elseif tag == "ir.Value.LocalVar" then return false
     elseif tag == "ir.Value.Function" then return true
     else
-        error("impossible")
+        typedecl.tag_error(tag)
     end
 end
 

pallene/print_ir.lua

@@ -6,6 +6,7 @@
 local C = require "pallene.C"
 local ir = require "pallene.ir"
 local util = require "pallene.util"
+local typedecl = require "pallene.typedecl"
 
 --
 -- Generates a human-readable representation of the IR.
@@ -41,7 +42,7 @@ local function Val(val)
     elseif tag == "ir.Value.LocalVar" then return Var(val.id)
     elseif tag == "ir.Value.Function" then return Fun(val.id)
     else
-        error("impossible")
+        typedecl.tag_error(tag)
     end
 end
 
@@ -214,7 +215,8 @@ local function Cmd(cmd)
     elseif tag == "ir.Cmd.CallStatic" then rhs = Call(Fun(cmd.f_id),  Vals(cmd.srcs))
     elseif tag == "ir.Cmd.CallDyn"    then rhs = Call(Val(cmd.src_f), Vals(cmd.srcs))
     else
-        local tagname = assert(string.match(cmd._tag, "^ir.Cmd.(.*)"))
+        local tagname = cmd._tag
+        assert(typedecl.match_tag(tagname, "ir.Cmd"))
         rhs = Call(tagname, Vals(ir.get_srcs(cmd)))
     end
 

pallene/to_ir.lua

@@ -93,7 +93,7 @@ function ToIR:convert_toplevel(prog_ast)
             self.rec_id_of_typ[typ] = ir.add_record_type(self.module, typ)
 
         else
-            error("impossible")
+            typedecl.tag_error(tag)
         end
     end
 
@@ -248,7 +248,7 @@ function ToIR:convert_stat(cmds, stat)
                     local id = self.glb_id_of_decl[cname.decl]
                     table.insert(lhss, to_ir.LHS.Global(id))
                 else
-                    error("impossible")
+                    typedecl.tag_error(cname._tag)
                 end
 
             elseif var._tag == "ast.Var.Bracket" then
@@ -266,12 +266,14 @@ function ToIR:convert_stat(cmds, stat)
                 elseif ttag == "types.T.Record" then
                     local typ = var.exp._type
                     table.insert(lhss, to_ir.LHS.Record(typ, t, var.name))
+                elseif typedecl.tag_is_type(ttag) then
+                    typedecl.tag_error(ttag, "type not indexable.")
                 else
-                    error("impossible")
+                    typedecl.tag_error(ttag)
                 end
 
             else
-                error("impossible")
+                typedecl.tag_error(var._tag)
             end
         end
 
@@ -326,7 +328,7 @@ function ToIR:convert_stat(cmds, stat)
                 elseif ltag == "to_ir.LHS.Record" then
                     cmd = ir.Cmd.SetField(loc, lhs.typ, lhs.rec, lhs.field, val)
                 else
-                    error("impossible")
+                    typedecl.tag_error(ltag)
                 end
                 table.insert(cmds, cmd)
             end
@@ -355,7 +357,7 @@ function ToIR:convert_stat(cmds, stat)
         table.insert(cmds, ir.Cmd.Break())
 
     else
-        error("impossible")
+        typedecl.type_error(tag)
     end
 end
 
@@ -498,7 +500,7 @@ function ToIR:exp_to_value(cmds, exp, _recursive)
                 error("not implemented")
 
             else
-                error("impossible")
+                typedecl.tag_error(cname._tag)
             end
         else
             -- Fallthrough to default
@@ -577,7 +579,7 @@ function ToIR:exp_to_assignment(cmds, dst, exp)
                 table.insert(cmds, ir.Cmd.SetField(exp.loc, typ, dv, field_name, vv))
             end
         else
-            error("impossible")
+            typedecl.tag_error(typ._tag)
         end
 
     elseif tag == "ast.Exp.Lambda" then
@@ -649,7 +651,7 @@ function ToIR:exp_to_assignment(cmds, dst, exp)
                 assert(#xs == 1)
                 table.insert(cmds, ir.Cmd.BuiltinTostring(loc, dsts, xs))
             else
-                error("impossible")
+                typedecl.tag_error(bname)
             end
 
         elseif cname and cname._tag == "checker.Name.Function" then
@@ -691,13 +693,16 @@ function ToIR:exp_to_assignment(cmds, dst, exp)
                 cmd = ir.Cmd.GetTable(loc, dst_typ, dst, rec, key)
             elseif typ._tag == "types.T.Record" then
                 cmd = ir.Cmd.GetField(loc, typ, dst, rec, field)
+            elseif typedecl.tag_is_type(typ._tag) then
+                typedecl.tag_error(typ._tag, "cannot index this type.")
             else
-                error("impossible")
+                typedecl.tag_error(typ._tag)
             end
+
             table.insert(cmds, cmd)
 
         else
-            error("impossible")
+            typedecl.tag_error(var._tag)
         end
 
     elseif tag == "ast.Exp.Unop" then
@@ -775,7 +780,8 @@ function ToIR:exp_to_assignment(cmds, dst, exp)
             elseif src_typ._tag == "types.T.Any" then
                 table.insert(cmds, ir.Cmd.FromDyn(loc, dst_typ, dst, v))
             else
-                error("impossible")
+                error(string.format("error casting from type '%s' to '%s'",
+                        types.tostring(src_typ), types.tostring(dst_typ)))
             end
         end
 
@@ -803,8 +809,10 @@ function ToIR:value_is_truthy(cmds, exp, val)
         local b = ir.add_local(self.func, false, types.T.Boolean())
         table.insert(cmds, ir.Cmd.IsTruthy(exp.loc, b, val))
         return ir.Value.LocalVar(b)
+    elseif typedecl.tag_is_type(typ) then
+        typedecl.tag_error(typ._tag, "unable to test this type for truthiness.")
     else
-        error("impossible")
+        typedecl.tag_error(typ._tag)
     end
 end