Collapse empty call expressions (#1308)

* Collapse empty call expressions

* Unset ForceMultiLine in rewrite.go so parse tree doesn't change when formatting

build/print.go

@@ -955,6 +955,10 @@ func (p *printer) useCompactMode(start *Position, list *[]Expr, end *End, mode s
 	if mode == modeSeq {
 		return true
 	}
+	// Use compact mode for empty call expressions if ForceMultiLine is not set
+	if mode == modeCall && len(*list) == 0 && !forceMultiLine {
+		return true
+	}
 
 	// In the Default and .bzl printing modes try to keep the original printing style.
 	// Non-top-level statements and lists of arguments of a function definition

build/rewrite.go

@@ -138,6 +138,7 @@ var rewrites = []struct {
 	{"reorderarguments", reorderArguments, scopeBoth},
 	{"editoctal", editOctals, scopeBoth},
 	{"editfloat", editFloats, scopeBoth},
+	{"collapseEmpty", collapseEmpty, scopeBoth},
 }
 
 // leaveAlone reports whether any of the nodes on the stack are marked
@@ -1459,3 +1460,17 @@ func removeParens(f *File, _ *Rewriter) {
 
 	Edit(f, simplify)
 }
+
+// collapseEmpty unsets ForceMultiLine for empty call expressions.
+func collapseEmpty(f *File, _ *Rewriter) {
+	Walk(f, func(expr Expr, stack []Expr) {
+		c, ok := expr.(*CallExpr)
+		if !ok {
+			return
+		}
+
+		if len(c.List) == 0 { // No arguments
+			c.ForceMultiLine = false
+		}
+	})
+}

build/testdata/076.golden

@@ -0,0 +1,18 @@
+# Test collapse empty call expressions
+
+func()
+
+func()
+
+# before comment
+func()
+
+func()  # after comment
+
+func(
+    # line comment
+)
+
+func(
+    name = "not_empty",
+)

build/testdata/076.in

@@ -0,0 +1,22 @@
+# Test collapse empty call expressions
+
+func(
+)
+
+func(
+)
+
+# before comment
+func(
+)
+
+func(
+)  # after comment
+
+func(
+    # line comment
+)
+
+func(
+    name = "not_empty",
+)