fix: be consistent in not reporting newlines between trace nodes to info view (#7143)

This PR makes the server consistently not report newlines between trace
nodes to the info view, enabling it to render them on dedicates lines
without extraneous spacing between them in all circumstances.

The info view code will separately need to be adjusted to this new
behavior, until then this change will make adjacent trace node leafs
consistently be rendered *on the same line* if there is sufficient
space. The cmdline should be unaffected in any case.

src/Lean/Message.lean

@@ -241,6 +241,11 @@ partial def formatAux : NamingContext → Option MessageDataContext → MessageD
   | nCtx, ctx,       compose d₁ d₂            => return (← formatAux nCtx ctx d₁) ++ (← formatAux nCtx ctx d₂)
   | nCtx, ctx,       group d                  => Format.group <$> formatAux nCtx ctx d
   | nCtx, ctx,       trace data header children => do
+    let childFmts ← children.mapM (formatAux nCtx ctx)
+    if data.cls.isAnonymous then
+      -- Sequence of top-level traces collected by `addTraceAsMessages`, do not indent.
+      return .joinSep childFmts.toList "\n"
+
     let mut msg := f!"[{data.cls}]"
     if data.startTime != 0 then
       msg := f!"{msg} [{data.stopTime - data.startTime}]"
@@ -250,7 +255,6 @@ partial def formatAux : NamingContext → Option MessageDataContext → MessageD
       if maxNum > 0 && children.size > maxNum then
         children := children.take maxNum |>.push <|
           ofFormat f!"{children.size - maxNum} more entries... (increase `maxTraceChildren` to see more)"
-    let childFmts ← children.mapM (formatAux nCtx ctx)
     return .nest 2 (.joinSep (msg::childFmts.toList) "\n")
   | nCtx, ctx?,      ofLazy pp _             => do
     let dyn ← pp (ctx?.map (mkPPContext nCtx))

src/Lean/Util/Trace.lean

@@ -380,7 +380,9 @@ def addTraceAsMessages [Monad m] [MonadRef m] [MonadLog m] [MonadTrace m] : m Un
     pos2traces := pos2traces.insert (pos, endPos) <| pos2traces.getD (pos, endPos) #[] |>.push traceElem.msg
   let traces' := pos2traces.toArray.qsort fun ((a, _), _) ((b, _), _) => a < b
   for ((pos, endPos), traceMsg) in traces' do
-    let data := .tagged `trace <| .joinSep traceMsg.toList "\n"
+    -- cmdline and info view differ in how they insert newlines in between trace nodes so we just
+    -- put them in a synthetic root node for now and let the rendering functions handle this case
+    let data := .tagged `trace <| .trace { cls := .anonymous } .nil traceMsg
     logMessage <| Elab.mkMessageCore (← getFileName) (← getFileMap) data .information pos endPos
 
 end Lean

src/Lean/Widget/InteractiveDiagnostic.lean

@@ -149,6 +149,12 @@ where
   | ctx,      compose d₁ d₂            => do let d₁ ← go nCtx ctx d₁; let d₂ ← go nCtx ctx d₂; pure $ d₁ ++ d₂
   | ctx,      group d                  => Format.group <$> go nCtx ctx d
   | ctx,      .trace data header children => do
+    if data.cls.isAnonymous then
+      -- Sequence of top-level traces collected by `addTraceAsMessages`, do not indent.
+      -- As with nested sibling nodes, we do not separate them with newlines but rely on the client
+      -- to never put trace nodes on the same line.
+      return .join (← children.mapM (go nCtx ctx)).toList
+
     let mut header := (← go nCtx ctx header).nest 4
     if data.startTime != 0 then
       header := f!"[{data.stopTime - data.startTime}] {header}"

tests/lean/run/traceFormat.lean

@@ -0,0 +1,62 @@
+import Lean.CoreM
+
+/-!
+Tests formatting of traces in various combinations, on the cmdline automatically via `#guard_msgs`
+and in the info view via manual testing.
+-/
+
+open Lean
+
+def withNode (cls : Name) (msg : MessageData) (k : CoreM Unit) (collapsed := true) (tag := "") : CoreM Unit := do
+  let oldTraces ← getTraces
+  modifyTraces fun _ => {}
+  k
+  let ref ← getRef
+  let mut data := { cls, collapsed, tag }
+  let msg := .trace data msg ((← getTraces).toArray.map (·.msg))
+  modifyTraces fun _ =>
+    oldTraces.push { ref, msg }
+
+/--
+info: [test] top-level leaf
+[test] top-level leaf
+[test] node with single leaf
+  [test] leaf
+[test] node with adjacent leafs
+  [test] leaf
+  [test] leaf
+[test] nested nodes
+  [test] leaf
+  [test] node
+    [test] leaf
+  [test] leaf
+[test] uncollapsed node
+  [test] leaf
+  [test] node
+    [test] leaf
+  [test] leaf
+[test] node with nested newline
+  [test] line1
+      line2
+-/
+#guard_msgs in
+#eval show CoreM Unit from do
+  addTrace `test "top-level leaf"
+  addTrace `test "top-level leaf"
+  withNode `test "node with single leaf" do
+    addTrace `test "leaf"
+  withNode `test "node with adjacent leafs" do
+    addTrace `test "leaf"
+    addTrace `test "leaf"
+  withNode `test "nested nodes" do
+    addTrace `test "leaf"
+    withNode `test "node" do
+      addTrace `test "leaf"
+    addTrace `test "leaf"
+  withNode `test "uncollapsed node" (collapsed := false) do
+    addTrace `test "leaf"
+    withNode `test "node" do
+      addTrace `test "leaf"
+    addTrace `test "leaf"
+  withNode `test "node with nested newline" do
+    addTrace `test "line1\nline2"