fix: namespace completion to only use the short name (#8350)

This PR changes namespace completion to use the same algorithm as
declaration identifier completion, which makes it use the short name
(last name component) for completions instead of the full name, avoiding
namespace duplications.

Closes #5654

Author: Rob23oba

src/Lean/Server/Completion/CompletionCollectors.lean

@@ -209,43 +209,43 @@ section IdCompletionUtils
             (Name.mkStr p (s.extract 0 ⟨newLen - optDot - len⟩), newLen)
     (go id).1
 
-  def matchNamespace (ns : Name) (nsFragment : Name) (danglingDot : Bool) : Bool :=
-    if danglingDot then
-      if nsFragment != ns && nsFragment.isPrefixOf ns then
-        true
-      else
-        false
-    else
-      match ns, nsFragment with
-      | .str p₁ s₁, .str p₂ s₂ =>
-        if p₁ == p₂ then s₂.charactersIn s₁ else false
-      | _, _ => false
+  def bestLabelForDecl? (ctx : ContextInfo) (declName : Name) (id : Name) (danglingDot : Bool) :
+      M (Option Name) := Prod.snd <$> StateT.run (s := none) do
+    let matchUsingNamespace (ns : Name) : StateT (Option Name) M Unit := do
+      let some label ← matchDecl? ns id danglingDot declName
+        | return
+      modify fun
+        | none =>
+          some label
+        | some bestLabel =>
+          -- for open namespaces `A` and `A.B` and a decl `A.B.c`, pick the decl `c` over `B.c`
+          if label.isSuffixOf bestLabel then
+            some label
+          else
+            some bestLabel
+    let rec visitNamespaces (ns : Name) : StateT (Option Name) M Unit := do
+      let Name.str p .. := ns
+        | return ()
+      matchUsingNamespace ns
+      visitNamespaces p
+    -- use current namespace
+    visitNamespaces ctx.currNamespace
+    -- use open decls
+    for openDecl in ctx.openDecls do
+      let OpenDecl.simple ns exs := openDecl
+        | pure ()
+      if exs.contains declName then
+        continue
+      matchUsingNamespace ns
+    matchUsingNamespace Name.anonymous
 
   def completeNamespaces (ctx : ContextInfo) (id : Name) (danglingDot : Bool) : M Unit := do
     let env ← getEnv
-    let add (ns : Name) (ns' : Name) : M Unit :=
-      if danglingDot then
-        addNamespaceCompletionItem (ns.replacePrefix (ns' ++ id) Name.anonymous)
-      else
-        addNamespaceCompletionItem (ns.replacePrefix ns' Name.anonymous)
     env.getNamespaceSet |>.forM fun ns => do
       unless ns.isInternal || env.contains ns do -- Ignore internal and namespaces that are also declaration names
-        for openDecl in ctx.openDecls do
-          match openDecl with
-          | OpenDecl.simple ns' _      =>
-            if matchNamespace ns (ns' ++ id) danglingDot then
-              add ns ns'
-              return ()
-          | _ => pure ()
-        -- use current namespace
-        let rec visitNamespaces (ns' : Name) : M Unit := do
-          if matchNamespace ns (ns' ++ id) danglingDot then
-            add ns ns'
-          else
-            match ns' with
-            | Name.str p .. => visitNamespaces p
-            | _ => return ()
-        visitNamespaces ctx.currNamespace
+        let label? ← bestLabelForDecl? ctx ns id danglingDot
+        if let some bestLabel := label? then
+          addNamespaceCompletionItem bestLabel
 
 end IdCompletionUtils
 
@@ -258,7 +258,7 @@ section DotCompletionUtils
       | _ => false
     if isConstOf then
       return true
-    let some e ← unfoldeDefinitionGuarded? e | return false
+    let some e ← unfoldDefinitionGuarded? e | return false
     isDefEqToAppOf e declName
 
   private def isDotCompletionMethod (typeName : Name) (info : ConstantInfo) : MetaM Bool :=
@@ -356,34 +356,7 @@ private def idCompletionCore
   -- search for matches in the environment
   let env ← getEnv
   forEligibleDeclsWithCancellationM fun declName c => do
-    let bestMatch? ← (·.2) <$> StateT.run (s := none) do
-      let matchUsingNamespace (ns : Name) : StateT (Option Name) M Unit := do
-        let some label ← matchDecl? ns id danglingDot declName
-          | return
-        modify fun
-          | none =>
-            some label
-          | some bestLabel =>
-            -- for open namespaces `A` and `A.B` and a decl `A.B.c`, pick the decl `c` over `B.c`
-            if label.isSuffixOf bestLabel then
-              some label
-            else
-              some bestLabel
-      let rec visitNamespaces (ns : Name) : StateT (Option Name) M Unit := do
-        let Name.str p .. := ns
-          | return ()
-        matchUsingNamespace ns
-        visitNamespaces p
-      -- use current namespace
-      visitNamespaces ctx.currNamespace
-      -- use open decls
-      for openDecl in ctx.openDecls do
-        let OpenDecl.simple ns exs := openDecl
-          | pure ()
-        if exs.contains declName then
-          continue
-        matchUsingNamespace ns
-      matchUsingNamespace Name.anonymous
+    let bestMatch? ← bestLabelForDecl? ctx declName id danglingDot
     if let some bestLabel := bestMatch? then
       addUnresolvedCompletionItem bestLabel (.const declName) (← getCompletionKindForDecl c)
   RequestCancellation.check

src/Lean/Server/Completion/CompletionUtils.lean

@@ -66,7 +66,7 @@ where
     else
       shortenIn id contextNamespace.getPrefix
 
-def unfoldeDefinitionGuarded? (e : Expr) : MetaM (Option Expr) :=
+def unfoldDefinitionGuarded? (e : Expr) : MetaM (Option Expr) :=
   try Lean.Meta.unfoldDefinition? e catch _ => pure none
 
 partial def getDotCompletionTypeNames (type : Expr) : MetaM (Array Name) :=
@@ -78,7 +78,7 @@ where
     if isStructure (← getEnv) typeName then
       for parentName in (← getAllParentStructures typeName) do
         modify fun s => s.push parentName
-    let some type ← unfoldeDefinitionGuarded? type | return ()
+    let some type ← unfoldDefinitionGuarded? type | return ()
     visit type
 
 end Lean.Server.Completion

tests/lean/interactive/compNamespace.lean.expected.out

@@ -37,7 +37,7 @@
 {"textDocument": {"uri": "file:///compNamespace.lean"},
  "position": {"line": 16, "character": 16}}
 {"items":
- [{"label": "Foo.LongNamespaceExample",
+ [{"label": "LongNamespaceExample",
    "kind": 9,
    "detail": "namespace",
    "data":