go/minformat: fix several formatting issues

Signed-off-by: Iskander Sharipov <quasilyte@gmail.com>

Author: quasilyte

go/minformat/minifier.go

@@ -105,9 +105,7 @@ func (m *minifier) printExpr(n ast.Expr) {
 		m.out.WriteByte(']')
 
 	case *ast.BinaryExpr:
-		m.printExpr(n.X)
-		m.out.WriteString(n.Op.String())
-		m.printExpr(n.Y)
+		m.printBinaryExpr(n)
 
 	case *ast.UnaryExpr:
 		m.out.WriteString(n.Op.String())
@@ -229,12 +227,18 @@ func (m *minifier) printStmt(n ast.Stmt) {
 		}
 
 	case *ast.AssignStmt:
-		for _, lhs := range n.Lhs {
+		for i, lhs := range n.Lhs {
 			m.printExpr(lhs)
+			if i != len(n.Lhs)-1 {
+				m.out.WriteByte(',')
+			}
 		}
 		m.out.WriteString(n.Tok.String())
-		for _, rhs := range n.Rhs {
+		for i, rhs := range n.Rhs {
 			m.printExpr(rhs)
+			if i != len(n.Rhs)-1 {
+				m.out.WriteByte(',')
+			}
 		}
 
 	case *ast.IncDecStmt:
@@ -481,6 +485,24 @@ func (m *minifier) printGenDecl(n *ast.GenDecl) {
 	}
 }
 
+func (m *minifier) printBinaryExpr(n *ast.BinaryExpr) {
+	// Handle `x < -y` and `x - -y`.
+	if n.Op == token.LSS || n.Op == token.SUB {
+		y := leftmostExpr(n.Y)
+		if y, ok := y.(*ast.UnaryExpr); ok && y.Op == token.SUB {
+			m.printExpr(n.X)
+			m.out.WriteString(n.Op.String())
+			m.out.WriteByte(' ')
+			m.printExpr(n.Y)
+			return
+		}
+	}
+
+	m.printExpr(n.X)
+	m.out.WriteString(n.Op.String())
+	m.printExpr(n.Y)
+}
+
 func (m *minifier) printFuncType(n *ast.FuncType) {
 	m.out.WriteString("(")
 	m.printFieldList(n.Params, ',')

go/minformat/minifier_test.go

@@ -56,6 +56,10 @@ func TestMinifyStmt(t *testing.T) {
 		{`x ++`, `x++`},
 		{`x [0 ] --`, `x[0]--`},
 
+		{`x = f()`, `x=f()`},
+		{`x, y = f()`, `x,y=f()`},
+		{`x, y = a, b`, `x,y=a,b`},
+
 		{`{ }`, `{}`},
 		{`{ 1; }`, `{1}`},
 		{`{ 1; 2 }`, `{1;2}`},
@@ -194,6 +198,13 @@ func TestMinifyExpr(t *testing.T) {
 		{`interface{ foo(); bar() }`, `interface{foo();bar()}`},
 		{`interface{ foo(int); bar() (int, error) }`, `interface{foo(int);bar()(int,error)}`},
 		{`interface { Embedded; foo() }`, `interface{Embedded;foo()}`},
+
+		// We need a space between `<` and `-`; otherwise it'll be parsed differently.
+		{`x < -y`, `x< -y`},
+		{`d < -35*Second`, `d< -35*Second`},
+
+		// We need a space between `-` and another `-`; otherwise it'll be parsed differently.
+		{`x - -1`, `x- -1`},
 	}
 
 	var m minifier

go/minformat/utils.go

@@ -0,0 +1,14 @@
+package minformat
+
+import (
+	"go/ast"
+)
+
+func leftmostExpr(n ast.Expr) ast.Expr {
+	switch n := n.(type) {
+	case *ast.BinaryExpr:
+		return leftmostExpr(n.X)
+	default:
+		return n
+	}
+}