From db3f952b1f3c996085cb9bfe846590084f8fae2e Mon Sep 17 00:00:00 2001 From: Robert Griesemer Date: Mon, 5 Jun 2023 09:30:58 -0700 Subject: [PATCH] cmd/compile/internal/syntax: better error message when using = instead of == When = is used instead of == as part of a conditional expression, the parser message emphasizes the LHS and RHS of = by always parenthesizing the two sides. For example, for: if x = y {} the error is: cannot use assignment (x) = (y) as value This is done to highlight the LHS and RHS in case of more complex cases such as if x || y = z {} which one may incorrectly read as (x) || (y == z) rather than the correct (x || y) = z. This CL fine-tunes the error message a bit by only adding the parentheses if the LHS and RHS are binary expressions. Fixes #60599. For #23385. Change-Id: Ida4c8d12464cc2ac15c934f24858eb6f43cf9950 Reviewed-on: https://go-review.googlesource.com/c/go/+/500975 Reviewed-by: Robert Findley Run-TryBot: Robert Griesemer Reviewed-by: Robert Griesemer Auto-Submit: Robert Griesemer TryBot-Result: Gopher Robot --- src/cmd/compile/internal/syntax/parser.go | 17 +++++++++++++---- .../internal/syntax/testdata/issue60599.go | 11 +++++++++++ 2 files changed, 24 insertions(+), 4 deletions(-) create mode 100644 src/cmd/compile/internal/syntax/testdata/issue60599.go diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go index c8b8ab0601..b5602fcff7 100644 --- a/src/cmd/compile/internal/syntax/parser.go +++ b/src/cmd/compile/internal/syntax/parser.go @@ -2369,10 +2369,8 @@ done: // further confusion. var str string if as, ok := s.(*AssignStmt); ok && as.Op == 0 { - // Emphasize Lhs and Rhs of assignment with parentheses to highlight '='. - // Do it always - it's not worth going through the trouble of doing it - // only for "complex" left and right sides. - str = "assignment (" + String(as.Lhs) + ") = (" + String(as.Rhs) + ")" + // Emphasize complex Lhs and Rhs of assignment with parentheses to highlight '='. + str = "assignment " + emphasize(as.Lhs) + " = " + emphasize(as.Rhs) } else { str = String(s) } @@ -2383,6 +2381,17 @@ done: return } +// emphasize returns a string representation of x, with (top-level) +// binary expressions emphasized by enclosing them in parentheses. +func emphasize(x Expr) string { + s := String(x) + if op, _ := x.(*Operation); op != nil && op.Y != nil { + // binary expression + return "(" + s + ")" + } + return s +} + func (p *parser) ifStmt() *IfStmt { if trace { defer p.trace("ifStmt")() diff --git a/src/cmd/compile/internal/syntax/testdata/issue60599.go b/src/cmd/compile/internal/syntax/testdata/issue60599.go new file mode 100644 index 0000000000..711d97bde0 --- /dev/null +++ b/src/cmd/compile/internal/syntax/testdata/issue60599.go @@ -0,0 +1,11 @@ +// Copyright 2023 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package p + +func _(x, y, z int) { + if x /* ERROR cannot use assignment x = y as value */ = y {} + if x || y /* ERROR cannot use assignment \(x || y\) = z as value */ = z {} + if x /* ERROR cannot use assignment x = \(y || z\) as value */ = y || z {} +} -- 2.48.1