cmd/compile: avoid follow-on errors for literals with syntax errors

- only convert literal strings if there were no syntax errors
  (some of the conversion routines exit if there is an error)
- mark nodes for literals with syntax errors to avoid follow-on
  errors
- don't attempt to import packages whose path had syntax errors

Fixes #32133.

Change-Id: I1803ad48c65abfecf6f48ddff1e27eded5e282c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/192437Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/noder.go

@@ -309,6 +309,10 @@ func (p *noder) decls(decls []syntax.Decl) (l []*Node) {
 }
 
 func (p *noder) importDecl(imp *syntax.ImportDecl) {
+	if imp.Path.Bad {
+		return // avoid follow-on errors if there was a syntax error
+	}
+
 	val := p.basicLit(imp.Path)
 	ipkg := importfile(&val)
 
@@ -602,7 +606,9 @@ func (p *noder) expr(expr syntax.Expr) *Node {
 	case *syntax.Name:
 		return p.mkname(expr)
 	case *syntax.BasicLit:
-		return nodlit(p.basicLit(expr))
+		n := nodlit(p.basicLit(expr))
+		n.SetDiag(expr.Bad) // avoid follow-on errors if there was a syntax error
+		return n
 	case *syntax.CompositeLit:
 		n := p.nod(expr, OCOMPLIT, nil, nil)
 		if expr.Type != nil {
@@ -1351,55 +1357,60 @@ func checkLangCompat(lit *syntax.BasicLit) {
 }
 
 func (p *noder) basicLit(lit *syntax.BasicLit) Val {
-	// TODO: Don't try to convert if we had syntax errors (conversions may fail).
-	//       Use dummy values so we can continue to compile. Eventually, use a
-	//       form of "unknown" literals that are ignored during type-checking so
-	//       we can continue type-checking w/o spurious follow-up errors.
+	// We don't use the errors of the conversion routines to determine
+	// if a literal string is valid because the conversion routines may
+	// accept a wider syntax than the language permits. Rely on lit.Bad
+	// instead.
 	switch s := lit.Value; lit.Kind {
 	case syntax.IntLit:
 		checkLangCompat(lit)
 		x := new(Mpint)
-		x.SetString(s)
+		if !lit.Bad {
+			x.SetString(s)
+		}
 		return Val{U: x}
 
 	case syntax.FloatLit:
 		checkLangCompat(lit)
 		x := newMpflt()
-		x.SetString(s)
+		if !lit.Bad {
+			x.SetString(s)
+		}
 		return Val{U: x}
 
 	case syntax.ImagLit:
 		checkLangCompat(lit)
 		x := newMpcmplx()
-		x.Imag.SetString(strings.TrimSuffix(s, "i"))
+		if !lit.Bad {
+			x.Imag.SetString(strings.TrimSuffix(s, "i"))
+		}
 		return Val{U: x}
 
 	case syntax.RuneLit:
-		var r rune
-		if u, err := strconv.Unquote(s); err == nil && len(u) > 0 {
-			// Package syntax already reported any errors.
-			// Check for them again though because 0 is a
-			// better fallback value for invalid rune
-			// literals than 0xFFFD.
+		x := new(Mpint)
+		x.Rune = true
+		if !lit.Bad {
+			u, _ := strconv.Unquote(s)
+			var r rune
 			if len(u) == 1 {
 				r = rune(u[0])
 			} else {
 				r, _ = utf8.DecodeRuneInString(u)
 			}
+			x.SetInt64(int64(r))
 		}
-		x := new(Mpint)
-		x.SetInt64(int64(r))
-		x.Rune = true
 		return Val{U: x}
 
 	case syntax.StringLit:
-		if len(s) > 0 && s[0] == '`' {
-			// strip carriage returns from raw string
-			s = strings.Replace(s, "\r", "", -1)
+		var x string
+		if !lit.Bad {
+			if len(s) > 0 && s[0] == '`' {
+				// strip carriage returns from raw string
+				s = strings.Replace(s, "\r", "", -1)
+			}
+			x, _ = strconv.Unquote(s)
 		}
-		// Ignore errors because package syntax already reported them.
-		u, _ := strconv.Unquote(s)
-		return Val{U: u}
+		return Val{U: x}
 
 	default:
 		panic("unhandled BasicLit kind")

test/fixedbugs/issue32133.go

+// errorcheck
+
+// Copyright 2019 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
+
+// errors for the //line-adjusted code below
+// ERROR "newline in string"
+// ERROR "newline in character literal"
+// ERROR "newline in string"
+// ERROR "string not terminated"
+
+//line :10:1
+import "foo
+
+//line :19:1
+func _() {
+	0x // ERROR "hexadecimal literal has no digits"
+}
+
+func _() {
+	0x1.0 // ERROR "hexadecimal mantissa requires a 'p' exponent"
+}
+
+func _() {
+	0_i // ERROR "'_' must separate successive digits"
+}
+
+func _() {
+//line :11:1
+	'
+}
+
+func _() {
+//line :12:1
+	"
+}
+
+func _() {
+//line :13:1
+	`
\ No newline at end of file