From d24d34e18d4443ae5365044aaa0bce40a3dd853c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Mart=C3=AD?= <mvdan@mvdan.cc>
Date: Tue, 12 May 2020 23:47:29 +0100
Subject: [PATCH] make "split long lines" idempotent

---
 format/format.go                | 109 +++++++++++++++++---------------
 testdata/scripts/long-lines.txt |  14 ++--
 2 files changed, 68 insertions(+), 55 deletions(-)

diff --git a/format/format.go b/format/format.go
index 9f5e98c..5576f72 100644
--- a/format/format.go
+++ b/format/format.go
@@ -97,6 +97,7 @@ func File(fset *token.FileSet, file *ast.File, opts Options) {
 		return true
 	}
 	post := func(c *astutil.Cursor) bool {
+		f.applyPost(c)
 		switch c.Node().(type) {
 		case *ast.FieldList:
 			f.longLineExtra = 0
@@ -267,7 +268,6 @@ func (f *fumpter) lineEnd(line int) token.Pos {
 // "go:generate", to prevent matching false positives like "https://site".
 var rxCommentDirective = regexp.MustCompile(`^([a-z]+:[a-z]+|line\b|export\b|extern\b|sys(nb)?\b|nolint\b)`)
 
-// visit takes either an ast.Node or a []ast.Stmt.
 func (f *fumpter) applyPre(c *astutil.Cursor) {
 	f.splitLongLine(c)
 
@@ -465,6 +465,63 @@ func (f *fumpter) applyPre(c *astutil.Cursor) {
 
 		f.removeLinesBetween(node.Lbrace, bodyPos)
 
+	case *ast.CaseClause:
+		f.stmts(node.Body)
+		openLine := f.Line(node.Case)
+		closeLine := f.Line(node.Colon)
+		if openLine == closeLine {
+			// nothing to do
+			break
+		}
+		if len(f.commentsBetween(node.Case, node.Colon)) > 0 {
+			// don't move comments
+			break
+		}
+		if f.printLength(node) > shortLineLimit {
+			// too long to collapse
+			break
+		}
+		f.removeLines(openLine, closeLine)
+
+	case *ast.CommClause:
+		f.stmts(node.Body)
+
+	case *ast.FieldList:
+		if node.NumFields() == 0 {
+			// Empty field lists should not contain a newline.
+			openLine := f.Line(node.Pos())
+			closeLine := f.Line(node.End())
+			f.removeLines(openLine, closeLine)
+		}
+
+		// Merging adjacent fields (e.g. parameters) is disabled by default.
+		if !f.ExtraRules {
+			break
+		}
+		switch c.Parent().(type) {
+		case *ast.FuncDecl, *ast.FuncType, *ast.InterfaceType:
+			node.List = f.mergeAdjacentFields(node.List)
+			c.Replace(node)
+		case *ast.StructType:
+			// Do not merge adjacent fields in structs.
+		}
+
+	case *ast.BasicLit:
+		// Octal number literals were introduced in 1.13.
+		if semver.Compare(f.LangVersion, "v1.13") >= 0 {
+			if node.Kind == token.INT && rxOctalInteger.MatchString(node.Value) {
+				node.Value = "0o" + node.Value[1:]
+				c.Replace(node)
+			}
+		}
+	}
+}
+
+func (f *fumpter) applyPost(c *astutil.Cursor) {
+	switch node := c.Node().(type) {
+	// Adding newlines to composite literals happens as a "post" step, so
+	// that we can take into account whether "pre" steps added any newlines
+	// that would affect us here.
 	case *ast.CompositeLit:
 		if len(node.Elts) == 0 {
 			// doesn't have elements
@@ -529,56 +586,6 @@ func (f *fumpter) applyPre(c *astutil.Cursor) {
 				f.addNewline(elem1.End())
 			}
 		}
-
-	case *ast.CaseClause:
-		f.stmts(node.Body)
-		openLine := f.Line(node.Case)
-		closeLine := f.Line(node.Colon)
-		if openLine == closeLine {
-			// nothing to do
-			break
-		}
-		if len(f.commentsBetween(node.Case, node.Colon)) > 0 {
-			// don't move comments
-			break
-		}
-		if f.printLength(node) > shortLineLimit {
-			// too long to collapse
-			break
-		}
-		f.removeLines(openLine, closeLine)
-
-	case *ast.CommClause:
-		f.stmts(node.Body)
-
-	case *ast.FieldList:
-		if node.NumFields() == 0 {
-			// Empty field lists should not contain a newline.
-			openLine := f.Line(node.Pos())
-			closeLine := f.Line(node.End())
-			f.removeLines(openLine, closeLine)
-		}
-
-		// Merging adjacent fields (e.g. parameters) is disabled by default.
-		if !f.ExtraRules {
-			break
-		}
-		switch c.Parent().(type) {
-		case *ast.FuncDecl, *ast.FuncType, *ast.InterfaceType:
-			node.List = f.mergeAdjacentFields(node.List)
-			c.Replace(node)
-		case *ast.StructType:
-			// Do not merge adjacent fields in structs.
-		}
-
-	case *ast.BasicLit:
-		// Octal number literals were introduced in 1.13.
-		if semver.Compare(f.LangVersion, "v1.13") >= 0 {
-			if node.Kind == token.INT && rxOctalInteger.MatchString(node.Value) {
-				node.Value = "0o" + node.Value[1:]
-				c.Replace(node)
-			}
-		}
 	}
 }
 
diff --git a/testdata/scripts/long-lines.txt b/testdata/scripts/long-lines.txt
index e67978c..ea9f69f 100644
--- a/testdata/scripts/long-lines.txt
+++ b/testdata/scripts/long-lines.txt
@@ -1,6 +1,9 @@
-gofumpt -w .
+gofumpt -w foo.go
 cmp foo.go foo.go.golden
 
+gofumpt -d foo.go.golden
+! stdout .
+
 -- foo.go --
 package p
 
@@ -82,15 +85,18 @@ func _() {
 
 	// Allow splitting at the start of sub-lists too.
 	if err := f(argument1, argument2, argument3, argument4, argument5, argument6, someComplex{
-		argument7, argument8, argument9}); err != nil {
+		argument7, argument8, argument9,
+	}); err != nil {
 		panic(err)
 	}
 	if err := f(argument1, argument2, argument3, argument4, argument5, argument6, &someComplex{
-		argument7, argument8, argument9}); err != nil {
+		argument7, argument8, argument9,
+	}); err != nil {
 		panic(err)
 	}
 	if err := f(argument1, argument2, argument3, argument4, argument5, argument6, []someSlice{
-		argument7, argument8, argument9}); err != nil {
+		argument7, argument8, argument9,
+	}); err != nil {
 		panic(err)
 	}
 }