From 19bda2628c53fc89837868e2ae77ae03eb8c750e Mon Sep 17 00:00:00 2001
From: Andy Dienes <andydienes@gmail.com>
Date: Mon, 23 Feb 2026 11:52:59 -0500
Subject: [PATCH 1/4] enforce issimpleenoughtype in fast path for tmerge for
 PartialStruct

---
 Compiler/src/typelimits.jl | 4 +++-
 Compiler/test/inference.jl | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/Compiler/src/typelimits.jl b/Compiler/src/typelimits.jl
index 99f5c4185067f..fe1161f455782 100644
--- a/Compiler/src/typelimits.jl
+++ b/Compiler/src/typelimits.jl
@@ -677,7 +677,9 @@ end
 
 @nospecializeinfer function tmerge(lattice::PartialsLattice, @nospecialize(typea), @nospecialize(typeb))
     r = tmerge_fast_path(lattice, typea, typeb)
-    r !== nothing && return r
+    if r !== nothing
+        return (isa(r, PartialStruct) && !issimpleenoughtype(r.typ)) ? widenconst(r) : r
+    end
 
     # type-lattice for Const and PartialStruct wrappers
     aps = isa(typea, PartialStruct)
diff --git a/Compiler/test/inference.jl b/Compiler/test/inference.jl
index eb559caca3717..40e45fe0136c6 100644
--- a/Compiler/test/inference.jl
+++ b/Compiler/test/inference.jl
@@ -6563,4 +6563,10 @@ throwconditional(c, x) = c ? throw(x isa Int) : throw(x isa Float64)
     throwconditional(c, x)
 end == Bool
 
+# issue #60715
+let
+    f() = 1; f(_, x...) = (0, f(x...))
+    @test f(1, 2, 3) == (0, (0, (0, 1)))
+end
+
 end # module inference

From d9b477ab27a7165477623342cfc205d30483472b Mon Sep 17 00:00:00 2001
From: Andy Dienes <andydienes@gmail.com>
Date: Mon, 23 Feb 2026 13:56:49 -0500
Subject: [PATCH 2/4] catch in issimplertype rather than after tmerge_fast_path

---
 Compiler/src/typelimits.jl |  5 ++---
 Compiler/test/inference.jl | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/Compiler/src/typelimits.jl b/Compiler/src/typelimits.jl
index fe1161f455782..d6f1ba91dec0f 100644
--- a/Compiler/src/typelimits.jl
+++ b/Compiler/src/typelimits.jl
@@ -338,6 +338,7 @@ end
     typea === typeb && return true
     if typea isa PartialStruct
         aty = widenconst(typea)
+        issimpleenoughtype(aty) || return false
         if typeb isa Const || typeb isa PartialStruct
             @assert n_initialized(typea) ≤ n_initialized(typeb) "typeb ⊑ typea is assumed"
         elseif typeb isa PartialStruct
@@ -677,9 +678,7 @@ end
 
 @nospecializeinfer function tmerge(lattice::PartialsLattice, @nospecialize(typea), @nospecialize(typeb))
     r = tmerge_fast_path(lattice, typea, typeb)
-    if r !== nothing
-        return (isa(r, PartialStruct) && !issimpleenoughtype(r.typ)) ? widenconst(r) : r
-    end
+    r !== nothing && return r
 
     # type-lattice for Const and PartialStruct wrappers
     aps = isa(typea, PartialStruct)
diff --git a/Compiler/test/inference.jl b/Compiler/test/inference.jl
index 40e45fe0136c6..874824d41a7ff 100644
--- a/Compiler/test/inference.jl
+++ b/Compiler/test/inference.jl
@@ -5077,6 +5077,22 @@ let 𝕃ᵢ = Compiler.fallback_lattice
     @test t.fields == Any[Const(42), Int]
 end
 
+# issue #60715
+let 𝕃 = Compiler.fallback_lattice
+    local fn, fn1, pn, pn1
+    F(n) = iszero(n) ? Union{} : Tuple{Int, Union{Int, F(n-1)}}
+    P(n) = (f = F(n); Compiler.PartialStruct(𝕃, f, [Const(0), fieldtype(f, 2)]))
+
+    n = 0
+    while Compiler.issimpleenoughtype(F(n+1))
+        n += 1
+        fn, fn1, pn, pn1 = F(n), F(n+1), P(n), P(n+1)
+        @test Compiler.:⊑(𝕃, pn, pn1)
+    end
+    @test !Compiler.issimplertype(𝕃, pn1, pn)
+    @test !isa(Compiler.tmerge(𝕃, pn, pn1), Compiler.PartialStruct)
+end
+
 foo_empty_vararg(i...) = i[2]
 bar_empty_vararg(i) = foo_empty_vararg(10, 20, 30, i...)
 @test bar_empty_vararg(Union{}[]) === 20

From 0696471347e05de4084e04ce98a750a64ba26428 Mon Sep 17 00:00:00 2001
From: Andy Dienes <51664769+adienes@users.noreply.github.com>
Date: Mon, 23 Feb 2026 15:59:10 -0500
Subject: [PATCH 3/4] Update Compiler/src/typelimits.jl

Co-authored-by: Jameson Nash <vtjnash@gmail.com>
---
 Compiler/src/typelimits.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Compiler/src/typelimits.jl b/Compiler/src/typelimits.jl
index d6f1ba91dec0f..337a673e6b20f 100644
--- a/Compiler/src/typelimits.jl
+++ b/Compiler/src/typelimits.jl
@@ -338,7 +338,7 @@ end
     typea === typeb && return true
     if typea isa PartialStruct
         aty = widenconst(typea)
-        issimpleenoughtype(aty) || return false
+        issimplertype(aty, widenconst(bty)) || return false
         if typeb isa Const || typeb isa PartialStruct
             @assert n_initialized(typea) ≤ n_initialized(typeb) "typeb ⊑ typea is assumed"
         elseif typeb isa PartialStruct

From 4ab4c38cc5c6289cadfc3d5463711b4aa60a0142 Mon Sep 17 00:00:00 2001
From: Andy Dienes <andydienes@gmail.com>
Date: Mon, 23 Feb 2026 16:06:49 -0500
Subject: [PATCH 4/4] fixup

---
 Compiler/src/typelimits.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Compiler/src/typelimits.jl b/Compiler/src/typelimits.jl
index 337a673e6b20f..2d025221c77b9 100644
--- a/Compiler/src/typelimits.jl
+++ b/Compiler/src/typelimits.jl
@@ -338,7 +338,7 @@ end
     typea === typeb && return true
     if typea isa PartialStruct
         aty = widenconst(typea)
-        issimplertype(aty, widenconst(bty)) || return false
+        issimplertype(𝕃, aty, widenconst(typeb)) || return false
         if typeb isa Const || typeb isa PartialStruct
             @assert n_initialized(typea) ≤ n_initialized(typeb) "typeb ⊑ typea is assumed"
         elseif typeb isa PartialStruct