cmd/compile/internal/syntax: differentiate between ';' and '\n' in syntax errors

Towards better syntax error messages: With this change, the parser knows whether
a semicolon was an actual ';' in the source, or whether it was an automatically
inserted semicolon as result of a '\n' or EOF. Using this information in error
messages makes them more understandable.

For #17328.

Change-Id: I8cd9accee8681b62569d0ecef922d38682b401eb
Reviewed-on: https://go-review.googlesource.com/36636
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go
index 3ebc670950f05323d7e3463eb308163fd841ac33..f016a6adbe3fa9d70175b0200ffff81dea03ad84 100644 (file)
--- a/src/cmd/compile/internal/syntax/parser.go
+++ b/src/cmd/compile/internal/syntax/parser.go
@@ -144,7 +144,7 @@ func (p *parser) syntax_error_at(pos src.Pos, msg string) {
        // determine token string
        var tok string
        switch p.tok {
-       case _Name:
+       case _Name, _Semi:
                tok = p.lit
        case _Literal:
                tok = "literal " + p.lit
@@ -215,7 +215,7 @@ func tokstring(tok token) string {
        case _Comma:
                return "comma"
        case _Semi:
-               return "semicolon or newline"
+               return "semicolon"
        }
        return tok.String()
 }

diff --git a/src/cmd/compile/internal/syntax/scanner.go b/src/cmd/compile/internal/syntax/scanner.go
index 149827b21c683b43ce3bc3665e79e83d050d1454..ede3b00a342a0f37fc5976eab479adfdf3d03ab5 100644 (file)
--- a/src/cmd/compile/internal/syntax/scanner.go
+++ b/src/cmd/compile/internal/syntax/scanner.go
@@ -27,7 +27,7 @@ type scanner struct {
        // current token, valid after calling next()
        line, col uint
        tok       token
-       lit       string   // valid if tok is _Name or _Literal
+       lit       string   // valid if tok is _Name, _Literal, or _Semi ("semicolon", "newline", or "EOF")
        kind      LitKind  // valid if tok is _Literal
        op        Operator // valid if tok is _Operator, _AssignOp, or _IncOp
        prec      int      // valid if tok is _Operator, _AssignOp, or _IncOp
@@ -73,12 +73,14 @@ redo:
        switch c {
        case -1:
                if nlsemi {
+                       s.lit = "EOF"
                        s.tok = _Semi
                        break
                }
                s.tok = _EOF
 
        case '\n':
+               s.lit = "newline"
                s.tok = _Semi
 
        case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
@@ -106,6 +108,7 @@ redo:
                s.tok = _Comma
 
        case ';':
+               s.lit = "semicolon"
                s.tok = _Semi
 
        case ')':
@@ -185,6 +188,7 @@ redo:
                        if s.source.line > s.line && nlsemi {
                                // A multi-line comment acts like a newline;
                                // it translates to a ';' if nlsemi is set.
+                               s.lit = "newline"
                                s.tok = _Semi
                                break
                        }

diff --git a/src/cmd/compile/internal/syntax/scanner_test.go b/src/cmd/compile/internal/syntax/scanner_test.go
index fcdc3348e4ed0bac325d83f91ebf24bf4fb9fd30..ed240df069da9ba868c0dfa2867a3ff7dea8959b 100644 (file)
--- a/src/cmd/compile/internal/syntax/scanner_test.go
+++ b/src/cmd/compile/internal/syntax/scanner_test.go
@@ -66,6 +66,11 @@ func TestTokens(t *testing.T) {
                }
 
                switch want.tok {
+               case _Semi:
+                       if got.lit != "semicolon" {
+                               t.Errorf("got %s; want semicolon", got.lit)
+                       }
+
                case _Name, _Literal:
                        if got.lit != want.src {
                                t.Errorf("got lit = %q; want %q", got.lit, want.src)
@@ -94,6 +99,9 @@ func TestTokens(t *testing.T) {
                                t.Errorf("got tok = %s; want ;", got.tok)
                                continue
                        }
+                       if got.lit != "newline" {
+                               t.Errorf("got %s; want newline", got.lit)
+                       }
                }
 
                got.next()

diff --git a/test/fixedbugs/issue14520.go b/test/fixedbugs/issue14520.go
index 1b1f4dedd336f740e606348010aecd23d137156e..84d240faf0a14981e5182c139fed80f7e7a56fef 100644 (file)
--- a/test/fixedbugs/issue14520.go
+++ b/test/fixedbugs/issue14520.go
@@ -9,6 +9,6 @@ package f
 import /* // ERROR "import path" */ `
 bogus`
 
-func f(x int /* // ERROR "unexpected semicolon"
+func f(x int /* // ERROR "unexpected newline"
 
 */)

diff --git a/test/syntax/semi6.go b/test/syntax/semi6.go
index 325cc274255f146efcbf3d971f26c98601ba8c38..4a04f89ddb107043157c9c397d3367433963b06d 100644 (file)
--- a/test/syntax/semi6.go
+++ b/test/syntax/semi6.go
@@ -6,6 +6,6 @@
 
 package main
 
-type T // ERROR "unexpected semicolon or newline in type declaration"
-// line below uncommented to avoid follow-up error
-// {
\ No newline at end of file
+type T1        // ERROR "unexpected newline in type declaration"
+
+type T2 /* // ERROR "unexpected EOF in type declaration" */
\ No newline at end of file