fix: omit fvars from simp_all? theorem list (leanprover#2969)

Removes local hypotheses from the simp theorem list generated by
`simp_all?`.

Fixes: leanprover#2953

---

Supersedes PR leanprover#1862

src/Lean/Elab/Tactic/Simp.lean

@@ -264,7 +264,14 @@ register_builtin_option tactic.simp.trace : Bool := {
   descr    := "When tracing is enabled, calls to `simp` or `dsimp` will print an equivalent `simp only` call."
 }
 
-def traceSimpCall (stx : Syntax) (usedSimps : UsedSimps) : MetaM Unit := do
+/--
+If `stx` is the syntax of a `simp`, `simp_all` or `dsimp` tactic invocation, and
+`usedSimps` is the set of simp lemmas used by this invocation, then `mkSimpOnly`
+creates the syntax of an equivalent `simp only`, `simp_all only` or `dsimp only`
+invocation.
+-/
+def mkSimpOnly (stx : Syntax) (usedSimps : UsedSimps) : MetaM Syntax := do
+  let isSimpAll := stx.isOfKind ``Parser.Tactic.simpAll
   let mut stx := stx
   if stx[3].isNone then
     stx := stx.setArg 3 (mkNullNode #[mkAtom "only"])
@@ -281,6 +288,12 @@ def traceSimpCall (stx : Syntax) (usedSimps : UsedSimps) : MetaM Unit := do
         else
           (← `(Parser.Tactic.simpLemma| $(mkIdent (← unresolveNameGlobal declName)):ident)))
     | .fvar fvarId => -- local hypotheses in the context
+      -- `simp_all` always uses all propositional hypotheses (and it can't use
+      -- any others). So `simp_all only [h]`, where `h` is a hypothesis, would
+      -- be redundant. It would also be confusing since it suggests that only
+      -- `h` is used.
+      if isSimpAll then
+        continue
       if let some ldecl := lctx.find? fvarId then
         localsOrStar := localsOrStar.bind fun locals =>
           if !ldecl.userName.isInaccessibleUserName && !ldecl.userName.hasMacroScopes &&
@@ -299,8 +312,10 @@ def traceSimpCall (stx : Syntax) (usedSimps : UsedSimps) : MetaM Unit := do
   else
     args := args.push (← `(Parser.Tactic.simpStar| *))
   let argsStx := if args.isEmpty then #[] else #[mkAtom "[", (mkAtom ",").mkSep args, mkAtom "]"]
-  stx := stx.setArg 4 (mkNullNode argsStx)
-  logInfoAt stx[0] m!"Try this: {stx}"
+  return stx.setArg 4 (mkNullNode argsStx)
+
+def traceSimpCall (stx : Syntax) (usedSimps : UsedSimps) : MetaM Unit := do
+  logInfoAt stx[0] m!"Try this: {← mkSimpOnly stx usedSimps}"
 
 /--
 `simpLocation ctx discharge? varIdToLemmaId loc`

tests/lean/simp_trace.lean

@@ -138,3 +138,15 @@ example (P : Prop) : P ∧ P ↔ P := by simp only [← my_thm']
 example {P : Prop} : P → P := by intro h; simp [*]
 
 example {P : Prop} : P → P := by intro; simp [*]
+
+-- `simp_all only [h]`, where `h` is a local hypothesis, is redundant and
+-- misleading since `simp_all` uses all local hypotheses anyway. `simp_all?`
+-- should therefore omit hypotheses from the suggested theorem list.
+
+example {P : Nat → Type} (h₁ : n = m) (h₂ : P m) : P n := by
+  simp_all
+  exact h₂
+
+example {Q : ∀ {n m : Nat}, n = m → Prop} {P : Nat → Type} (h₁ : n = m) (h₂ : P m) (h₃ : Q h₁) : P n := by
+  simp_all
+  exact h₂

tests/lean/simp_trace.lean.expected.out

@@ -124,3 +124,8 @@ Try this: simp only [h]
 [Meta.Tactic.simp.rewrite] h:1000, P ==> True
 Try this: simp only [*]
 [Meta.Tactic.simp.rewrite] a✝:1000, P ==> True
+Try this: simp_all only
+[Meta.Tactic.simp.rewrite] h₁:1000, n ==> m
+Try this: simp_all only
+[Meta.Tactic.simp.rewrite] h₁:1000, n ==> m
+[Meta.Tactic.simp.rewrite] h₁:1000, n ==> m