go/parser: better error messages for if/switch/for conditions/expressions

Fixes #7102.

LGTM=adonovan
R=adonovan
CC=golang-codereviews
https://golang.org/cl/56770045

diff --git a/src/pkg/go/parser/parser.go b/src/pkg/go/parser/parser.go
index 2ad3e4e55610974c904c9cb01c3b625b33477e30..c3e3ee859ab2f623c47634e0c5296b84054e3198 100644 (file)
--- a/src/pkg/go/parser/parser.go
+++ b/src/pkg/go/parser/parser.go
@@ -1762,14 +1762,14 @@ func (p *parser) parseBranchStmt(tok token.Token) *ast.BranchStmt {
        return &ast.BranchStmt{TokPos: pos, Tok: tok, Label: label}
 }
 
-func (p *parser) makeExpr(s ast.Stmt) ast.Expr {
+func (p *parser) makeExpr(s ast.Stmt, kind string) ast.Expr {
        if s == nil {
                return nil
        }
        if es, isExpr := s.(*ast.ExprStmt); isExpr {
                return p.checkExpr(es.X)
        }
-       p.error(s.Pos(), "expected condition, found simple statement (missing parentheses around composite literal?)")
+       p.error(s.Pos(), fmt.Sprintf("expected %s, found simple statement (missing parentheses around composite literal?)", kind))
        return &ast.BadExpr{From: s.Pos(), To: s.End()}
 }
 
@@ -1796,7 +1796,7 @@ func (p *parser) parseIfStmt() *ast.IfStmt {
                                p.next()
                                x = p.parseRhs()
                        } else {
-                               x = p.makeExpr(s)
+                               x = p.makeExpr(s, "boolean expression")
                                s = nil
                        }
                }
@@ -1927,7 +1927,7 @@ func (p *parser) parseSwitchStmt() ast.Stmt {
                return &ast.TypeSwitchStmt{Switch: pos, Init: s1, Assign: s2, Body: body}
        }
 
-       return &ast.SwitchStmt{Switch: pos, Init: s1, Tag: p.makeExpr(s2), Body: body}
+       return &ast.SwitchStmt{Switch: pos, Init: s1, Tag: p.makeExpr(s2, "switch expression"), Body: body}
 }
 
 func (p *parser) parseCommClause() *ast.CommClause {
@@ -2072,7 +2072,7 @@ func (p *parser) parseForStmt() ast.Stmt {
        return &ast.ForStmt{
                For:  pos,
                Init: s1,
-               Cond: p.makeExpr(s2),
+               Cond: p.makeExpr(s2, "boolean or range expression"),
                Post: s3,
                Body: body,
        }

diff --git a/src/pkg/go/parser/short_test.go b/src/pkg/go/parser/short_test.go
index 9d18d049000c9f22372b71e2df28c83d772a3c49..22f79930b372ef46b856b28912b579d54eceb532 100644 (file)
--- a/src/pkg/go/parser/short_test.go
+++ b/src/pkg/go/parser/short_test.go
@@ -48,14 +48,14 @@ var invalids = []string{
        `package p; func f() { if { /* ERROR "expected operand" */ } };`,
        `package p; func f() { if ; { /* ERROR "expected operand" */ } };`,
        `package p; func f() { if f(); { /* ERROR "expected operand" */ } };`,
-       `package p; func f() { if _ /* ERROR "expected condition" */ = range x; true {} };`,
-       `package p; func f() { switch _ /* ERROR "expected condition" */ = range x; true {} };`,
+       `package p; func f() { if _ /* ERROR "expected boolean expression" */ = range x; true {} };`,
+       `package p; func f() { switch _ /* ERROR "expected switch expression" */ = range x; true {} };`,
        `package p; func f() { for _ = range x ; /* ERROR "expected '{'" */ ; {} };`,
        `package p; func f() { for ; ; _ = range /* ERROR "expected operand" */ x {} };`,
-       `package p; func f() { for ; _ /* ERROR "expected condition" */ = range x ; {} };`,
-       `package p; func f() { switch t /* ERROR "expected condition" */ = t.(type) {} };`,
-       `package p; func f() { switch t /* ERROR "expected condition" */ , t = t.(type) {} };`,
-       `package p; func f() { switch t /* ERROR "expected condition" */ = t.(type), t {} };`,
+       `package p; func f() { for ; _ /* ERROR "expected boolean or range expression" */ = range x ; {} };`,
+       `package p; func f() { switch t /* ERROR "expected switch expression" */ = t.(type) {} };`,
+       `package p; func f() { switch t /* ERROR "expected switch expression" */ , t = t.(type) {} };`,
+       `package p; func f() { switch t /* ERROR "expected switch expression" */ = t.(type), t {} };`,
        `package p; var a = [ /* ERROR "expected expression" */ 1]int;`,
        `package p; var a = [ /* ERROR "expected expression" */ ...]int;`,
        `package p; var a = struct /* ERROR "expected expression" */ {}`,
@@ -82,6 +82,10 @@ var invalids = []string{
        `package p; func f() { var s []int; _ = s[: /* ERROR "2nd index required" */ :] };`,
        `package p; func f() { var s []int; _ = s[: /* ERROR "2nd index required" */ ::] };`,
        `package p; func f() { var s []int; _ = s[i:j:k: /* ERROR "expected ']'" */ l] };`,
+       `package p; func f() { for x /* ERROR "boolean or range expression" */ = []string {} }`,
+       `package p; func f() { for x /* ERROR "boolean or range expression" */ := []string {} }`,
+       `package p; func f() { for i /* ERROR "boolean or range expression" */ , x = []string {} }`,
+       `package p; func f() { for i /* ERROR "boolean or range expression" */ , x := []string {} }`,
 }
 
 func TestInvalid(t *testing.T) {