doc: add docstrings for dsimp configuration

src/Init/MetaTypes.lean

@@ -42,23 +42,67 @@ inductive EtaStructMode where
 
 namespace DSimp
 
+/--
+The configuration for `dsimp`.
+Passed to `dsimp` using, for example, the `dsimp (config := {zeta := false})` syntax.
+
+Implementation note: this structure is only used for processing the `(config := ...)` syntax, and it is not used internally.
+It is immediately converted to `Lean.Meta.Simp.Config` by `Lean.Elab.Tactic.elabSimpConfig`.
+-/
 structure Config where
-  /-- `let x := v; e[x]` reduces to `e[v]`. -/
+  /--
+  When `true` (default: `true`), performs zeta reduction of let expressions.
+  That is, `let x := v; e[x]` reduces to `e[v]`.
+  See also `zetaDelta`.
+  -/
   zeta              : Bool := true
+  /--
+  When `true` (default: `true`), performs beta reduction of applications of `fun` expressions.
+  That is, `(fun x => e[x]) v` reduces to `e[v]`.
+  -/
   beta              : Bool := true
+  /--
+  TODO (currently unimplemented). When `true` (default: `true`), performs eta reduction for `fun` expressions.
+  That is, `(fun x => f x)` reduces to `f`.
+  -/
   eta               : Bool := true
+  /--
+  Configures how to determine definitional equality between two structure instances.
+  See documentation for `Lean.Meta.EtaStructMode`.
+  -/
   etaStruct         : EtaStructMode := .all
+  /--
+  When `true` (default: `true`), reduces `match` expressions applied to constructors.
+  -/
   iota              : Bool := true
+  /--
+  When `true` (default: `true`), reduces projections of structure constructors.
+  -/
   proj              : Bool := true
+  /--
+  When `true` (default: `false`), rewrites a proposition `p` to `True` or `False` by inferring
+  a `Decidable p` instance and reducing it.
+  -/
   decide            : Bool := false
+  /--
+  When `true` (default: `false`), unfolds definitions.
+  This can be enabled using the `simp!` syntax.
+  -/
   autoUnfold        : Bool := false
-  /-- If `failIfUnchanged := true`, then calls to `simp`, `dsimp`, or `simp_all`
-  will fail if they do not make progress. -/
+  /--
+  If `failIfUnchanged` is `true` (default: `true`), then calls to `simp`, `dsimp`, or `simp_all`
+  will fail if they do not make progress.
+  -/
   failIfUnchanged   : Bool := true
-  /-- If `unfoldPartialApp := true`, then calls to `simp`, `dsimp`, or `simp_all`
-  will unfold even partial applications of `f` when we request `f` to be unfolded. -/
+  /--
+  If `unfoldPartialApp` is `true` (default: `false`), then calls to `simp`, `dsimp`, or `simp_all`
+  will unfold even partial applications of `f` when we request `f` to be unfolded.
+  -/
   unfoldPartialApp  : Bool := false
-  /-- Given a local context containing entry `x : t := e`, free variable `x` reduces to `e`. -/
+  /--
+  When `true` (default: `false`), local definitions are unfolded.
+  That is, given a local context containing entry `x : t := e`, the free variable `x` reduces to `e`.
+  -/
   zetaDelta         : Bool := false
   deriving Inhabited, BEq
 
@@ -72,7 +116,7 @@ def defaultMaxSteps := 100000
 The configuration for `simp`.
 Passed to `simp` using, for example, the `simp (config := {contextual := true})` syntax.
 
-See also `Lean.Meta.Simp.neutralConfig`.
+See also `Lean.Meta.Simp.neutralConfig` and `Lean.Meta.DSimp.Config`.
 -/
 structure Config where
   /--