From ffc0573b854ca2fc58ad85ad7599ec66f0a82b36 Mon Sep 17 00:00:00 2001 From: Robert Griesemer Date: Thu, 6 Feb 2020 15:32:40 -0800 Subject: [PATCH] cmd/compile/internal/syntax: better error when an assignment is used in value context The error message is now positioned at the statement position (which is an identifing token, such as the '=' for assignments); and in case of assignments it emphasizes the assignment by putting the Lhs and Rhs in parentheses. Finally, the wording is changed from "use of * as value" to the stronger "cannot use * as value" (for which there is precedent elsewhere in the parser). Fixes #36858. Change-Id: Ic3f101bba50f58e3a1d9b29645066634631f2d61 Reviewed-on: https://go-review.googlesource.com/c/go/+/218337 Reviewed-by: Matthew Dempsky --- src/cmd/compile/internal/syntax/parser.go | 11 ++++++++--- .../compile/internal/syntax/testdata/issue23385.src | 9 +++++++-- test/fixedbugs/issue18915.go | 6 +++--- test/syntax/chan1.go | 2 +- test/syntax/typesw.go | 2 +- 5 files changed, 20 insertions(+), 10 deletions(-) diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go index f3c2c60ec8..469d9ad69b 100644 --- a/src/cmd/compile/internal/syntax/parser.go +++ b/src/cmd/compile/internal/syntax/parser.go @@ -1886,11 +1886,16 @@ done: // which turns an expression into an assignment. Provide // a more explicit error message in that case to prevent // further confusion. - str := String(s) + var str string if as, ok := s.(*AssignStmt); ok && as.Op == 0 { - str = "assignment " + str + // 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) + ")" + } else { + str = String(s) } - p.syntaxError(fmt.Sprintf("%s used as value", str)) + p.syntaxErrorAt(s.Pos(), fmt.Sprintf("cannot use %s as value", str)) } p.xnest = outer diff --git a/src/cmd/compile/internal/syntax/testdata/issue23385.src b/src/cmd/compile/internal/syntax/testdata/issue23385.src index 44abcd7e23..2459a7369b 100644 --- a/src/cmd/compile/internal/syntax/testdata/issue23385.src +++ b/src/cmd/compile/internal/syntax/testdata/issue23385.src @@ -6,7 +6,12 @@ package p -func f() { - if true || 0 = 1 /* ERROR assignment .* used as value */ { +func _() { + if true || 0 /* ERROR cannot use assignment .* as value */ = 1 { + } +} + +func _(a, b string) { + if a == "a" && b /* ERROR cannot use assignment .* as value */ = "b" { } } diff --git a/test/fixedbugs/issue18915.go b/test/fixedbugs/issue18915.go index a432bbc17c..66e31e2556 100644 --- a/test/fixedbugs/issue18915.go +++ b/test/fixedbugs/issue18915.go @@ -10,12 +10,12 @@ package p func _() { - if a := 10 { // ERROR "a := 10 used as value" + if a := 10 { // ERROR "cannot use a := 10 as value" } - for b := 10 { // ERROR "b := 10 used as value" + for b := 10 { // ERROR "cannot use b := 10 as value" } - switch c := 10 { // ERROR "c := 10 used as value" + switch c := 10 { // ERROR "cannot use c := 10 as value" } } diff --git a/test/syntax/chan1.go b/test/syntax/chan1.go index 4eb63796ac..56103d1d79 100644 --- a/test/syntax/chan1.go +++ b/test/syntax/chan1.go @@ -10,7 +10,7 @@ var c chan int var v int func main() { - if c <- v { // ERROR "used as value" + if c <- v { // ERROR "cannot use c <- v as value" } } diff --git a/test/syntax/typesw.go b/test/syntax/typesw.go index f9120e8851..3781933978 100644 --- a/test/syntax/typesw.go +++ b/test/syntax/typesw.go @@ -7,7 +7,7 @@ package main func main() { - switch main() := interface{}(nil).(type) { // ERROR "invalid variable name|used as value" + switch main() := interface{}(nil).(type) { // ERROR "invalid variable name|cannot use .* as value" default: } } -- 2.50.0