go.tools/go/types: support for "soft" errors

Provide an extra field, "Soft" in types.Error.
A client may want to filter out soft errors and
only abort if there are "hard" errors.

Qualified a first set of errors as "soft".

Fixes golang/go#7360.

LGTM=adonovan
R=adonovan
CC=golang-codereviews
https://golang.org/cl/71800043

go/types/api.go

@@ -46,12 +46,15 @@ func Check(path string, fset *token.FileSet, files []*ast.File) (*Package, error
 	return pkg, nil
 }
 
-// An Error describes a type-checking error;
+// An Error describes a type-checking error; it implements the error interface.
-// it implements the error interface.
+// A "soft" error is an error that still permits a valid interpretation of a
+// package (such as "unused variable"); "hard" errors may lead to unpredictable
+// behavior if ignored.
 type Error struct {
 	Fset *token.FileSet // file set for interpretation of Pos
 	Pos  token.Pos      // error position
 	Msg  string         // error message
+	Soft bool           // if set, error is "soft"
 }
 
 // Error returns an error string formatted as follows:

go/types/errors.go

@@ -54,8 +54,8 @@ func (check *checker) dump(format string, args ...interface{}) {
 	fmt.Println(check.sprintf(format, args...))
 }
 
-func (check *checker) err(pos token.Pos, msg string) {
+func (check *checker) err(pos token.Pos, msg string, soft bool) {
-	err := Error{check.fset, pos, msg}
+	err := Error{check.fset, pos, msg, soft}
 	if check.firstErr == nil {
 		check.firstErr = err
 	}
@@ -66,8 +66,16 @@ func (check *checker) err(pos token.Pos, msg string) {
 	f(err)
 }
 
+func (check *checker) error(pos token.Pos, msg string) {
+	check.err(pos, msg, false)
+}
+
 func (check *checker) errorf(pos token.Pos, format string, args ...interface{}) {
-	check.err(pos, check.sprintf(format, args...))
+	check.err(pos, check.sprintf(format, args...), false)
+}
+
+func (check *checker) softErrorf(pos token.Pos, format string, args ...interface{}) {
+	check.err(pos, check.sprintf(format, args...), true)
 }
 
 func (check *checker) invalidAST(pos token.Pos, format string, args ...interface{}) {

go/types/expr.go

@@ -961,7 +961,7 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 	case *ast.Ellipsis:
 		// ellipses are handled explicitly where they are legal
 		// (array composite literals and parameter lists)
-		check.errorf(e.Pos(), "invalid use of '...'")
+		check.error(e.Pos(), "invalid use of '...'")
 		goto Error
 
 	case *ast.BasicLit:
@@ -1005,7 +1005,7 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 			}
 		}
 		if typ == nil {
-			check.errorf(e.Pos(), "missing type in composite literal")
+			check.error(e.Pos(), "missing type in composite literal")
 			goto Error
 		}
 
@@ -1021,7 +1021,7 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 				for _, e := range e.Elts {
 					kv, _ := e.(*ast.KeyValueExpr)
 					if kv == nil {
-						check.errorf(e.Pos(), "mixture of field:value and value elements in struct literal")
+						check.error(e.Pos(), "mixture of field:value and value elements in struct literal")
 						continue
 					}
 					key, _ := kv.Key.(*ast.Ident)
@@ -1055,12 +1055,12 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 				// no element must have a key
 				for i, e := range e.Elts {
 					if kv, _ := e.(*ast.KeyValueExpr); kv != nil {
-						check.errorf(kv.Pos(), "mixture of field:value and value elements in struct literal")
+						check.error(kv.Pos(), "mixture of field:value and value elements in struct literal")
 						continue
 					}
 					check.expr(x, e)
 					if i >= len(fields) {
-						check.errorf(x.pos(), "too many values in struct literal")
+						check.error(x.pos(), "too many values in struct literal")
 						break // cannot continue
 					}
 					// i < len(fields)
@@ -1073,7 +1073,7 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 					}
 				}
 				if len(e.Elts) < len(fields) {
-					check.errorf(e.Rbrace, "too few values in struct literal")
+					check.error(e.Rbrace, "too few values in struct literal")
 					// ok to continue
 				}
 			}
@@ -1093,7 +1093,7 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 			for _, e := range e.Elts {
 				kv, _ := e.(*ast.KeyValueExpr)
 				if kv == nil {
-					check.errorf(e.Pos(), "missing key in map literal")
+					check.error(e.Pos(), "missing key in map literal")
 					continue
 				}
 				check.expr(x, kv.Key)
@@ -1263,7 +1263,7 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 
 		// spec: "Only the first index may be omitted; it defaults to 0."
 		if slice3(e) && (e.High == nil || sliceMax(e) == nil) {
-			check.errorf(e.Rbrack, "2nd and 3rd index required in 3-index slice")
+			check.error(e.Rbrack, "2nd and 3rd index required in 3-index slice")
 			goto Error
 		}
 

go/types/labels.go

@@ -35,7 +35,7 @@ func (check *checker) labels(body *ast.BlockStmt) {
 	// spec: "It is illegal to define a label that is never used."
 	for _, obj := range all.elems {
 		if lbl := obj.(*Label); !lbl.used {
-			check.errorf(lbl.pos, "label %s declared but not used", lbl.name)
+			check.softErrorf(lbl.pos, "label %s declared but not used", lbl.name)
 		}
 	}
 }

go/types/resolver.go

@@ -311,8 +311,7 @@ func (check *checker) resolveFiles(files []*ast.File) {
 						check.recordDef(d.Name, obj)
 						// init functions must have a body
 						if d.Body == nil {
-							check.errorf(obj.pos, "missing function body")
+							check.softErrorf(obj.pos, "missing function body")
-							// ok to continue
 						}
 					} else {
 						check.declare(pkg.scope, d.Name, obj)
@@ -414,7 +413,7 @@ func (check *checker) resolveFiles(files []*ast.File) {
 				// Unused "blank imports" are automatically ignored
 				// since _ identifiers are not entered into scopes.
 				if !obj.used {
-					check.errorf(obj.pos, "%q imported but not used", obj.pkg.path)
+					check.softErrorf(obj.pos, "%q imported but not used", obj.pkg.path)
 				}
 			default:
 				// All other objects in the file scope must be dot-
@@ -432,7 +431,7 @@ func (check *checker) resolveFiles(files []*ast.File) {
 		// check if the corresponding package was used.
 		for pkg, pos := range dotImports[i] {
 			if !usedDotImports[pkg] {
-				check.errorf(pos, "%q imported but not used", pkg.path)
+				check.softErrorf(pos, "%q imported but not used", pkg.path)
 			}
 		}
 	}

go/types/stmt.go

@@ -43,7 +43,7 @@ func (check *checker) funcBody(decl *declInfo, name string, sig *Signature, body
 	}
 
 	if sig.results.Len() > 0 && !check.isTerminating(body, "") {
-		check.errorf(body.Rbrace, "missing return")
+		check.error(body.Rbrace, "missing return")
 	}
 
 	// spec: "Implementation restriction: A compiler may make it illegal to
@@ -56,7 +56,7 @@ func (check *checker) funcBody(decl *declInfo, name string, sig *Signature, body
 func (check *checker) usage(scope *Scope) {
 	for _, obj := range scope.elems {
 		if v, _ := obj.(*Var); v != nil && !v.used {
-			check.errorf(v.pos, "%s declared but not used", v.name)
+			check.softErrorf(v.pos, "%s declared but not used", v.name)
 		}
 	}
 	for _, scope := range scope.children {
@@ -186,7 +186,7 @@ L:
 		for t, pos := range seen {
 			if T == nil && t == nil || T != nil && t != nil && Identical(T, t) {
 				// talk about "case" rather than "type" because of nil case
-				check.errorf(e.Pos(), "duplicate case in type switch")
+				check.error(e.Pos(), "duplicate case in type switch")
 				check.errorf(pos, "\tprevious case %s", T) // secondary error, \t indented
 				continue L
 			}
@@ -340,7 +340,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 				check.initVars(res.vars, s.Results, s.Return)
 			}
 		} else if len(s.Results) > 0 {
-			check.errorf(s.Results[0].Pos(), "no result values expected")
+			check.error(s.Results[0].Pos(), "no result values expected")
 		}
 
 	case *ast.BranchStmt:
@@ -351,15 +351,15 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 		switch s.Tok {
 		case token.BREAK:
 			if ctxt&inBreakable == 0 {
-				check.errorf(s.Pos(), "break not in for, switch, or select statement")
+				check.error(s.Pos(), "break not in for, switch, or select statement")
 			}
 		case token.CONTINUE:
 			if ctxt&inContinuable == 0 {
-				check.errorf(s.Pos(), "continue not in for statement")
+				check.error(s.Pos(), "continue not in for statement")
 			}
 		case token.FALLTHROUGH:
 			if ctxt&fallthroughOk == 0 {
-				check.errorf(s.Pos(), "fallthrough statement out of place")
+				check.error(s.Pos(), "fallthrough statement out of place")
 			}
 		default:
 			check.invalidAST(s.Pos(), "branch statement: %s", s.Tok)
@@ -379,7 +379,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 		var x operand
 		check.expr(&x, s.Cond)
 		if x.mode != invalid && !isBoolean(x.typ) {
-			check.errorf(s.Cond.Pos(), "non-boolean condition in if statement")
+			check.error(s.Cond.Pos(), "non-boolean condition in if statement")
 		}
 		check.stmt(inner, s.Body)
 		if s.Else != nil {
@@ -526,7 +526,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 				v.used = true // avoid usage error when checking entire function
 			}
 			if !used {
-				check.errorf(lhs.Pos(), "%s declared but not used", lhs.Name)
+				check.softErrorf(lhs.Pos(), "%s declared but not used", lhs.Name)
 			}
 		}
 
@@ -563,7 +563,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 			}
 
 			if !valid {
-				check.errorf(clause.Comm.Pos(), "select case must be send or receive (possibly with assignment)")
+				check.error(clause.Comm.Pos(), "select case must be send or receive (possibly with assignment)")
 				continue
 			}
 
@@ -585,7 +585,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 			var x operand
 			check.expr(&x, s.Cond)
 			if x.mode != invalid && !isBoolean(x.typ) {
-				check.errorf(s.Cond.Pos(), "non-boolean condition in for statement")
+				check.error(s.Cond.Pos(), "non-boolean condition in for statement")
 			}
 		}
 		check.initStmt(s.Post)
@@ -703,7 +703,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 					check.declare(check.scope, nil, obj) // recordObject already called
 				}
 			} else {
-				check.errorf(s.TokPos, "no new variables on left side of :=")
+				check.error(s.TokPos, "no new variables on left side of :=")
 			}
 		} else {
 			// ordinary assignment
@@ -721,6 +721,6 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 		check.stmt(inner, s.Body)
 
 	default:
-		check.errorf(s.Pos(), "invalid statement")
+		check.error(s.Pos(), "invalid statement")
 	}
 }