chore(library/init): fix whitspaces before =>

tests/playground/patcheqnspace2.lean

@@ -0,0 +1,56 @@
+import init.lean.parser
+import init.lean.parser.transform
+open Lean
+open Lean.Parser
+
+def getAtomTrailingSpace : Syntax → Nat
+| Syntax.atom (some info) _ => info.trailing.stopPos - info.trailing.startPos
+| _ => 0
+
+def getMinTrailingSpace (ps : Array Syntax) (i : Nat) : Nat :=
+ps.foldl (fun acc (p : Syntax) =>
+  let space : Nat :=
+    match p.getTailInfo with
+    | some info => info.trailing.stopPos - info.trailing.startPos
+    | none => 0;
+  if space < acc then space else acc)
+  100000
+
+def reduceTrailingSpace : Syntax → Nat → Syntax
+| Syntax.atom (some info) val, delta => Syntax.atom (some { trailing := { stopPos := info.trailing.stopPos - delta, .. info.trailing }, .. info }) val
+
+| stx, _ => stx
+
+partial def fixPats : Array Syntax → Nat → Array Syntax
+| ps, i =>
+  let minSpace := getMinTrailingSpace ps i;
+  if minSpace <= 1 then
+    ps
+  else
+    let delta := minSpace - 1;
+    ps.map $ fun p => p.modifyArg i $ fun pat =>
+      match pat.getTailInfo with
+      | some info => pat.setTailInfo (some { trailing := { stopPos := info.trailing.stopPos - delta, .. info.trailing } , .. info })
+      | none => pat
+
+def fixEqnSyntax (stx : Syntax) : Syntax :=
+stx.rewriteBottomUp $ fun stx =>
+  stx.ifNodeKind `Lean.Parser.Command.declValEqns
+    (fun stx =>
+      stx.val.modifyArg 0 $ fun altsStx =>
+      altsStx.modifyArgs $ fun alts =>
+        let pats    := alts.map $ fun alt => alt.getArg 1;
+        let patSize := (pats.get 0).getArgs.size;
+        let pats    := fixPats pats (patSize - 1);
+        alts.mapIdx $ fun i alt => alt.setArg 1 (pats.get i))
+    (fun _ => stx)
+
+def main (xs : List String) : IO Unit :=
+do
+[fname] ← pure xs | throw (IO.userError "usage `patch <file-name>`");
+env ← mkEmptyEnvironment;
+stx ← parseFile env fname;
+let stx := fixEqnSyntax stx;
+match stx.reprint with
+| some out => IO.print out
+| none     => throw (IO.userError "failed to reprint")