From be9a1774f274e5333bef873868bb28b93918d8e7 Mon Sep 17 00:00:00 2001 From: Robert Griesemer Date: Wed, 10 Jan 2018 16:05:12 -0800 Subject: [PATCH] cmd/compile/internal/syntax: better error msg for some 'if' statements MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit R=go1.11 A common error is to write '=' instead of '==' inside the condition of a simple 'if' statement: if x = 0 { ... } Highlight the fact that we have an assignment in the error message to prevent further confusion. Fixes #23385. Change-Id: I1552050fd6da927bd12a1be0977bd2e98eca5885 Reviewed-on: https://go-review.googlesource.com/87316 Reviewed-by: Daniel Martí Reviewed-by: Matthew Dempsky --- src/cmd/compile/internal/syntax/parser.go | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go index 6b52950b94..d01ad6056e 100644 --- a/src/cmd/compile/internal/syntax/parser.go +++ b/src/cmd/compile/internal/syntax/parser.go @@ -170,9 +170,9 @@ func (p *parser) syntax_error_at(pos src.Pos, msg string) { switch { case msg == "": // nothing to do - case strings.HasPrefix(msg, "in"), strings.HasPrefix(msg, "at"), strings.HasPrefix(msg, "after"): + case strings.HasPrefix(msg, "in "), strings.HasPrefix(msg, "at "), strings.HasPrefix(msg, "after "): msg = " " + msg - case strings.HasPrefix(msg, "expecting"): + case strings.HasPrefix(msg, "expecting "): msg = ", " + msg default: // plain error - we don't care about current token @@ -1844,7 +1844,15 @@ done: case *ExprStmt: cond = s.X default: - p.syntax_error(fmt.Sprintf("%s used as value", String(s))) + // A common syntax error is to write '=' instead of '==', + // which turns an expression into an assignment. Provide + // a more explicit error message in that case to prevent + // further confusion. + str := String(s) + if as, ok := s.(*AssignStmt); ok && as.Op == 0 { + str = "assignment " + str + } + p.syntax_error(fmt.Sprintf("%s used as value", str)) } p.xnest = outer