feat: add optional (priority := <prio>) to instance command

src/Lean/Elab/Declaration.lean

@@ -45,10 +45,10 @@ def expandDeclNamespace? (stx : Syntax) : Option (Name × Syntax) :=
       | some (ns, declId) => some (ns, stx.setArg 1 (decl.setArg 1 declId))
       | none              => none
     else if k == `Lean.Parser.Command.instance then
-      let optDeclId := decl[2]
+      let optDeclId := decl[3]
       if optDeclId.isNone then none
       else match expandDeclIdNamespace? optDeclId[0] with
-        | some (ns, declId) => some (ns, stx.setArg 1 (decl.setArg 2 (optDeclId.setArg 0 declId)))
+        | some (ns, declId) => some (ns, stx.setArg 1 (decl.setArg 3 (optDeclId.setArg 0 declId)))
         | none              => none
     else
       none

src/Lean/Elab/DefView.lean

@@ -138,18 +138,20 @@ def mkDefViewOfConstant (modifiers : Modifiers) (stx : Syntax) : CommandElabM De
   }
 
 def mkDefViewOfInstance (modifiers : Modifiers) (stx : Syntax) : CommandElabM DefView := do
-  -- parser! attrKind >> "instance " >> optional declId >> declSig >> declVal
+  -- parser! Term.attrKind >> "instance " >> optNamedPrio >> optional declId >> declSig >> declVal
   let attrKind        ← toAttributeKind stx[0]
-  let (binders, type) := expandDeclSig stx[3]
-  let modifiers       := modifiers.addAttribute { kind := attrKind, name := `instance }
-  let declId ← match stx[2].getOptional? with
+  let prio            ← liftMacroM <| expandOptNamedPrio stx[2]
+  let attrStx         ← `(attr| instance $(quote prio):numLit)
+  let (binders, type) := expandDeclSig stx[4]
+  let modifiers       := modifiers.addAttribute { kind := attrKind, name := `instance, stx := attrStx }
+  let declId ← match stx[3].getOptional? with
     | some declId => pure declId
     | none        =>
       let id ← MkInstanceName.main type
       pure <| Syntax.node ``Parser.Command.declId #[mkIdentFrom stx id, mkNullNode]
   return {
     ref := stx, kind := DefKind.def, modifiers := modifiers,
-    declId := declId, binders := binders, type? := type, value := stx[4]
+    declId := declId, binders := binders, type? := type, value := stx[5]
   }
 
 def mkDefViewOfExample (modifiers : Modifiers) (stx : Syntax) : DefView :=

src/Lean/Elab/Syntax.lean

@@ -230,21 +230,6 @@ where
     | Name.str _ s _ => s ++ str
     | _ => str
 
-
-def expandOptNamedPrio (stx : Syntax) : MacroM Nat :=
-  if stx.isNone then
-    return evalPrio! default
-  else match stx[0] with
-    | `(Parser.Command.namedPrio| (priority := $prio)) => evalPrio prio
-    | _ => Macro.throwUnsupported
-
-def expandOptNamedName (stx : Syntax) : MacroM (Option Name) := do
-  if stx.isNone then
-    return none
-  else match stx[0] with
-    | `(Parser.Command.namedName| (name := $name)) => return name.getId
-    | _ => Macro.throwUnsupported
-
 /- We assume a new syntax can be treated as an atom when it starts and ends with a token.
    Here are examples of atom-like syntax.
    ```

src/Lean/Elab/Util.lean

@@ -4,6 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Leonardo de Moura
 -/
 import Lean.Util.Trace
+import Lean.Parser.Syntax
 import Lean.Parser.Extension
 import Lean.KeyedDeclsAttribute
 import Lean.Elab.Exception
@@ -26,6 +27,20 @@ def MacroScopesView.format (view : MacroScopesView) (mainModule : Name) : Format
 
 namespace Elab
 
+def expandOptNamedPrio (stx : Syntax) : MacroM Nat :=
+  if stx.isNone then
+    return evalPrio! default
+  else match stx[0] with
+    | `(Parser.Command.namedPrio| (priority := $prio)) => evalPrio prio
+    | _ => Macro.throwUnsupported
+
+def expandOptNamedName (stx : Syntax) : MacroM (Option Name) := do
+  if stx.isNone then
+    return none
+  else match stx[0] with
+    | `(Parser.Command.namedName| (name := $name)) => return name.getId
+    | _ => Macro.throwUnsupported
+
 structure MacroStackElem where
   before : Syntax
   after : Syntax

src/Lean/Meta/Instances.lean

@@ -55,10 +55,7 @@ builtin_initialize
     name  := `instance
     descr := "type class instance"
     add   := fun declName stx attrKind => do
-      let prio ← match stx with
-        | Syntax.missing => pure <| evalPrio! default -- small hack, in the elaborator we use `Syntax.missing` when creating attribute views for `instance
-        | _              => getAttrParamOptPrio stx[1]
-      -- TODO use prio
+      let prio ← getAttrParamOptPrio stx[1]
       discard <| addInstance declName attrKind prio |>.run {} {}
   }
 

src/Lean/Parser/Command.lean

@@ -18,6 +18,10 @@ namespace Parser
 @[builtinTermParser] def Term.quot := parser! "`(" >> toggleInsideQuot (termParser <|> many1Unbox commandParser) >> ")"
 
 namespace Command
+
+def namedPrio := parser! (atomic ("(" >> nonReservedSymbol "priority") >> " := " >> priorityParser >> ")")
+def optNamedPrio := optional namedPrio
+
 def commentBody : Parser :=
 { fn := rawFn (finishCommentBlock 1) true }
 
@@ -42,7 +46,7 @@ def «abbrev»         := parser! "abbrev " >> declId >> optDeclSig >> declVal
 def «def»            := parser! "def " >> declId >> optDeclSig >> declVal
 def «theorem»        := parser! "theorem " >> declId >> declSig >> declVal
 def «constant»       := parser! "constant " >> declId >> declSig >> optional declValSimple
-def «instance»       := parser! Term.attrKind >> "instance " >> optional declId >> declSig >> declVal
+def «instance»       := parser! Term.attrKind >> "instance " >> optNamedPrio >> optional declId >> declSig >> declVal
 def «axiom»          := parser! "axiom " >> declId >> declSig
 def «example»        := parser! "example " >> declSig >> declVal
 def inferMod         := parser! atomic (symbol "{" >> "}")

src/Lean/Parser/Syntax.lean

@@ -50,9 +50,7 @@ end Term
 
 namespace Command
 
-def namedPrio := parser! (atomic ("(" >> nonReservedSymbol "priority") >> " := " >> priorityParser >> ")")
 def namedName := parser! (atomic ("(" >> nonReservedSymbol "name") >> " := " >> ident >> ")")
-def optNamedPrio := optional namedPrio
 def optNamedName := optional namedName
 
 def «prefix»   := parser! "prefix"

tests/lean/run/instprio.lean

@@ -0,0 +1,17 @@
+class Def (α : Type u) where
+  val : α
+
+instance : Def Nat where
+  val := 10
+
+theorem ex1 : Def.val = 10 := rfl
+
+instance (priority := default+1) : Def Nat where
+  val := 20
+
+theorem ex2 : Def.val = 20 := rfl
+
+instance : Def Nat where
+  val := 30
+
+theorem ex3 : Def.val = 20 := rfl