Merge #34257

34257: pretty: make union and concat pointer receivers r=jordanlewis a=jordanlewis

Previously, union and concat were struct receivers in the Doc type,
which led to pathological hashing behavior when inserting into the
memoiDoc map. This commit switches them to pointer receivers, which
makes everything a lot faster.


```
name          old time/op    new time/op    delta
PrettyData-8     202ms ± 4%      66ms ± 2%  -67.35%  (p=0.000 n=10+10)

name          old alloc/op   new alloc/op   delta
PrettyData-8    24.7MB ± 0%    30.7MB ± 0%  +24.10%  (p=0.000 n=10+10)

name          old allocs/op  new allocs/op  delta
PrettyData-8     8.29k ± 0%     9.17k ± 0%  +10.59%  (p=0.000 n=10+10)
```

Helps #33649.

Release note: None

Co-authored-by: Jordan Lewis <[email protected]>

pkg/util/pretty/document.go

@@ -47,10 +47,10 @@ func (text) isDoc()      {}
 func (line) isDoc()      {}
 func (softbreak) isDoc() {}
 func (nilDoc) isDoc()    {}
-func (concat) isDoc()    {}
+func (*concat) isDoc()   {}
 func (nestt) isDoc()     {}
 func (nests) isDoc()     {}
-func (union) isDoc()     {}
+func (*union) isDoc()    {}
 func (*scolumn) isDoc()  {}
 func (*snesting) isDoc() {}
 func (pad) isDoc()       {}
@@ -105,7 +105,7 @@ type concat struct {
 // This uses simplifyNil to avoid actually inserting NIL docs
 // in the abstract tree.
 func Concat(a, b Doc) Doc {
-	return simplifyNil(a, b, func(a, b Doc) Doc { return concat{a, b} })
+	return simplifyNil(a, b, func(a, b Doc) Doc { return &concat{a, b} })
 }
 
 // nests represents (NESTS Int DOC) :: DOC -- nesting a doc "under" another.
@@ -149,7 +149,7 @@ type union struct {
 
 // Group will format d on one line if possible.
 func Group(d Doc) Doc {
-	return union{flatten(d), d}
+	return &union{flatten(d), d}
 }
 
 var textSpace = Text(" ")
@@ -158,7 +158,7 @@ func flatten(d Doc) Doc {
 	switch t := d.(type) {
 	case nilDoc:
 		return Nil
-	case concat:
+	case *concat:
 		return Concat(flatten(t.a), flatten(t.b))
 	case nestt:
 		return NestT(flatten(t.d))
@@ -170,7 +170,7 @@ func flatten(d Doc) Doc {
 		return textSpace
 	case softbreak:
 		return Nil
-	case union:
+	case *union:
 		return flatten(t.x)
 	case *scolumn:
 		return &scolumn{f: func(c int16) Doc { return flatten(t.f(c)) }}

pkg/util/pretty/pretty.go

@@ -123,7 +123,7 @@ func (b *beExec) be(k docPos, xlist *iDoc) *docBest {
 	switch t := d.d.(type) {
 	case nilDoc:
 		res = b.be(k, z)
-	case concat:
+	case *concat:
 		res = b.be(k, b.iDoc(d.i, t.a, b.iDoc(d.i, t.b, z)))
 	case nests:
 		res = b.be(k, b.iDoc(docPos{d.i.tabs, d.i.spaces + t.n}, t.d, z))
@@ -141,7 +141,7 @@ func (b *beExec) be(k docPos, xlist *iDoc) *docBest {
 			i:   d.i,
 			d:   b.be(d.i, z),
 		})
-	case union:
+	case *union:
 		res = b.better(k,
 			b.be(k, b.iDoc(d.i, t.x, z)),
 			// We eta-lift the second argument to avoid eager evaluation.

pkg/util/pretty/util.go

@@ -113,7 +113,7 @@ func AlignUnder(head, nested Doc) Doc {
 	g := Group(nested)
 	a := ConcatSpace(head, Align(g))
 	b := Concat(head, NestT(Concat(Line, g)))
-	return Group(union{a, b})
+	return Group(&union{a, b})
 }
 
 // Fold applies f recursively to all Docs in d.
@@ -282,7 +282,7 @@ func RLTable(align bool, rows ...RLTableRow) Doc {
 		}
 		alignedTable := Stack(items...)
 
-		finalDoc = union{alignedTable, nestedSections}
+		finalDoc = &union{alignedTable, nestedSections}
 	}
 
 	return Group(finalDoc)