cmd/vet: add ifaceassert and stringintconv checks

This change re-vendors x/tools to add the ifaceassert and stringintconv
checks to cmd/vet.

Fixes #32479.
Updates #4483.

Change-Id: I6bd30b0a3278592dfab4bd247036404ddaff09e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/221339
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

7 files changed, 240 insertions, 8 deletions

diff --git a/src/cmd/go.mod b/src/cmd/go.mod
index 0096c74e86..e1e5b34e6e 100644
--- a/src/cmd/go.mod
+++ b/src/cmd/go.mod
@@ -8,6 +8,5 @@ require (
 	golang.org/x/crypto v0.0.0-20200214034016-1d94cc7ab1c6
 	golang.org/x/mod v0.2.0
 	golang.org/x/sys v0.0.0-20200219091948-cb0a6d8edb6c // indirect
-	golang.org/x/tools v0.0.0-20200219195521-7c4b6277d74d
-	golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 // indirect
+	golang.org/x/tools v0.0.0-20200309180859-aa4048aca1ca
 )
diff --git a/src/cmd/go.sum b/src/cmd/go.sum
index 2bb6a9ab06..73eff83010 100644
--- a/src/cmd/go.sum
+++ b/src/cmd/go.sum
@@ -13,12 +13,13 @@ golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550 h1:ObdrDkeb4kJdCP557AjRjq
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20200214034016-1d94cc7ab1c6 h1:Sy5bstxEqwwbYs6n0/pBuxKENqOeZUgD45Gp3Q3pqLg=
 golang.org/x/crypto v0.0.0-20200214034016-1d94cc7ab1c6/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzBzNggFXnrqF1CaUcvgkdR5Ot7KZg=
 golang.org/x/mod v0.2.0 h1:KU7oHjnv3XNWfa5COkzUifxZmxp1TyI7ImMXqFxLwvQ=
 golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20200226121028-0de0cce0169b/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191204072324-ce4227a45e2e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -28,8 +29,8 @@ golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e h1:aZzprAO9/8oim3qStq3wc1Xuxx4QmAGriC4VU4ojemQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
-golang.org/x/tools v0.0.0-20200219195521-7c4b6277d74d h1:ZQ18He7VORO2x4IEBuwfdp56K+ftEzRjvL0cFuCGCcM=
-golang.org/x/tools v0.0.0-20200219195521-7c4b6277d74d/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
+golang.org/x/tools v0.0.0-20200309180859-aa4048aca1ca h1:cFQHQhDv9N1vc+64dtXDAyd3exHDGfRTtveOnD0IsLI=
+golang.org/x/tools v0.0.0-20200309180859-aa4048aca1ca/go.mod h1:o4KQGtdN14AW+yjsvvwRTJJuXz8XRtIHtEnmAXLyFUw=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898 h1:/atklqdjdhuosWIl6AIbOeHJjicWYPqR9bpxqxYG2pA=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/errorsas/errorsas.go b/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/errorsas/errorsas.go
index b80271afb9..384f025570 100644
--- a/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/errorsas/errorsas.go
+++ b/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/errorsas/errorsas.go
@@ -51,7 +51,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			return // not enough arguments, e.g. called with return values of another function
 		}
 		if fn.FullName() == "errors.As" && !pointerToInterfaceOrError(pass, call.Args[1]) {
-			pass.ReportRangef(call, "second argument to errors.As must be a pointer to an interface or a type implementing error")
+			pass.ReportRangef(call, "second argument to errors.As must be a non-nil pointer to either a type that implements error, or to any interface type")
 		}
 	})
 	return nil, nil
diff --git a/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/ifaceassert/ifaceassert.go b/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/ifaceassert/ifaceassert.go
new file mode 100644
index 0000000000..c5a71a7c57
--- /dev/null
+++ b/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/ifaceassert/ifaceassert.go
@@ -0,0 +1,101 @@
+// Copyright 2020 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 ifaceassert defines an Analyzer that flags
+// impossible interface-interface type assertions.
+package ifaceassert
+
+import (
+	"go/ast"
+	"go/types"
+
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/analysis/passes/inspect"
+	"golang.org/x/tools/go/ast/inspector"
+)
+
+const Doc = `detect impossible interface-to-interface type assertions
+
+This checker flags type assertions v.(T) and corresponding type-switch cases
+in which the static type V of v is an interface that cannot possibly implement
+the target interface T. This occurs when V and T contain methods with the same
+name but different signatures. Example:
+
+	var v interface {
+		Read()
+	}
+	_ = v.(io.Reader)
+
+The Read method in v has a different signature than the Read method in
+io.Reader, so this assertion cannot succeed.
+`
+
+var Analyzer = &analysis.Analyzer{
+	Name:     "ifaceassert",
+	Doc:      Doc,
+	Requires: []*analysis.Analyzer{inspect.Analyzer},
+	Run:      run,
+}
+
+// assertableTo checks whether interface v can be asserted into t. It returns
+// nil on success, or the first conflicting method on failure.
+func assertableTo(v, t types.Type) *types.Func {
+	// ensure that v and t are interfaces
+	V, _ := v.Underlying().(*types.Interface)
+	T, _ := t.Underlying().(*types.Interface)
+	if V == nil || T == nil {
+		return nil
+	}
+	if f, wrongType := types.MissingMethod(V, T, false); wrongType {
+		return f
+	}
+	return nil
+}
+
+func run(pass *analysis.Pass) (interface{}, error) {
+	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
+	nodeFilter := []ast.Node{
+		(*ast.TypeAssertExpr)(nil),
+		(*ast.TypeSwitchStmt)(nil),
+	}
+	inspect.Preorder(nodeFilter, func(n ast.Node) {
+		var (
+			assert  *ast.TypeAssertExpr // v.(T) expression
+			targets []ast.Expr          // interfaces T in v.(T)
+		)
+		switch n := n.(type) {
+		case *ast.TypeAssertExpr:
+			// take care of v.(type) in *ast.TypeSwitchStmt
+			if n.Type == nil {
+				return
+			}
+			assert = n
+			targets = append(targets, n.Type)
+		case *ast.TypeSwitchStmt:
+			// retrieve type assertion from type switch's 'assign' field
+			switch t := n.Assign.(type) {
+			case *ast.ExprStmt:
+				assert = t.X.(*ast.TypeAssertExpr)
+			case *ast.AssignStmt:
+				assert = t.Rhs[0].(*ast.TypeAssertExpr)
+			}
+			// gather target types from case clauses
+			for _, c := range n.Body.List {
+				targets = append(targets, c.(*ast.CaseClause).List...)
+			}
+		}
+		V := pass.TypesInfo.TypeOf(assert.X)
+		for _, target := range targets {
+			T := pass.TypesInfo.TypeOf(target)
+			if f := assertableTo(V, T); f != nil {
+				pass.Reportf(
+					target.Pos(),
+					"impossible type assertion: no type can implement both %v and %v (conflicting types for %v method)",
+					V, T, f.Name(),
+				)
+			}
+		}
+	})
+	return nil, nil
+}
diff --git a/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/stringintconv/string.go b/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/stringintconv/string.go
new file mode 100644
index 0000000000..ac2cd84ad3
--- /dev/null
+++ b/src/cmd/vendor/golang.org/x/tools/go/analysis/passes/stringintconv/string.go
@@ -0,0 +1,126 @@
+// Copyright 2020 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 stringintconv defines an Analyzer that flags type conversions
+// from integers to strings.
+package stringintconv
+
+import (
+	"fmt"
+	"go/ast"
+	"go/types"
+
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/analysis/passes/inspect"
+	"golang.org/x/tools/go/ast/inspector"
+)
+
+const Doc = `check for string(int) conversions
+
+This checker flags conversions of the form string(x) where x is an integer
+(but not byte or rune) type. Such conversions are discouraged because they
+return the UTF-8 representation of the Unicode code point x, and not a decimal
+string representation of x as one might expect. Furthermore, if x denotes an
+invalid code point, the conversion cannot be statically rejected.
+
+For conversions that intend on using the code point, consider replacing them
+with string(rune(x)). Otherwise, strconv.Itoa and its equivalents return the
+string representation of the value in the desired base.
+`
+
+var Analyzer = &analysis.Analyzer{
+	Name:     "stringintconv",
+	Doc:      Doc,
+	Requires: []*analysis.Analyzer{inspect.Analyzer},
+	Run:      run,
+}
+
+func typeName(typ types.Type) string {
+	if v, _ := typ.(interface{ Name() string }); v != nil {
+		return v.Name()
+	}
+	if v, _ := typ.(interface{ Obj() *types.TypeName }); v != nil {
+		return v.Obj().Name()
+	}
+	return ""
+}
+
+func run(pass *analysis.Pass) (interface{}, error) {
+	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
+	nodeFilter := []ast.Node{
+		(*ast.CallExpr)(nil),
+	}
+	inspect.Preorder(nodeFilter, func(n ast.Node) {
+		call := n.(*ast.CallExpr)
+
+		// Retrieve target type name.
+		var tname *types.TypeName
+		switch fun := call.Fun.(type) {
+		case *ast.Ident:
+			tname, _ = pass.TypesInfo.Uses[fun].(*types.TypeName)
+		case *ast.SelectorExpr:
+			tname, _ = pass.TypesInfo.Uses[fun.Sel].(*types.TypeName)
+		}
+		if tname == nil {
+			return
+		}
+		target := tname.Name()
+
+		// Check that target type T in T(v) has an underlying type of string.
+		T, _ := tname.Type().Underlying().(*types.Basic)
+		if T == nil || T.Kind() != types.String {
+			return
+		}
+		if s := T.Name(); target != s {
+			target += " (" + s + ")"
+		}
+
+		// Check that type V of v has an underlying integral type that is not byte or rune.
+		if len(call.Args) != 1 {
+			return
+		}
+		v := call.Args[0]
+		vtyp := pass.TypesInfo.TypeOf(v)
+		V, _ := vtyp.Underlying().(*types.Basic)
+		if V == nil || V.Info()&types.IsInteger == 0 {
+			return
+		}
+		switch V.Kind() {
+		case types.Byte, types.Rune, types.UntypedRune:
+			return
+		}
+
+		// Retrieve source type name.
+		source := typeName(vtyp)
+		if source == "" {
+			return
+		}
+		if s := V.Name(); source != s {
+			source += " (" + s + ")"
+		}
+		diag := analysis.Diagnostic{
+			Pos:     n.Pos(),
+			Message: fmt.Sprintf("conversion from %s to %s yields a string of one rune", source, target),
+			SuggestedFixes: []analysis.SuggestedFix{
+				{
+					Message: "Did you mean to convert a rune to a string?",
+					TextEdits: []analysis.TextEdit{
+						{
+							Pos:     v.Pos(),
+							End:     v.Pos(),
+							NewText: []byte("rune("),
+						},
+						{
+							Pos:     v.End(),
+							End:     v.End(),
+							NewText: []byte(")"),
+						},
+					},
+				},
+			},
+		}
+		pass.Report(diag)
+	})
+	return nil, nil
+}
diff --git a/src/cmd/vendor/modules.txt b/src/cmd/vendor/modules.txt
index 8bb7b7423e..9f4c9985c6 100644
--- a/src/cmd/vendor/modules.txt
+++ b/src/cmd/vendor/modules.txt
@@ -43,7 +43,7 @@ golang.org/x/mod/zip
 ## explicit
 golang.org/x/sys/unix
 golang.org/x/sys/windows
-# golang.org/x/tools v0.0.0-20200219195521-7c4b6277d74d
+# golang.org/x/tools v0.0.0-20200309180859-aa4048aca1ca
 ## explicit
 golang.org/x/tools/go/analysis
 golang.org/x/tools/go/analysis/internal/analysisflags
@@ -59,6 +59,7 @@ golang.org/x/tools/go/analysis/passes/copylock
 golang.org/x/tools/go/analysis/passes/ctrlflow
 golang.org/x/tools/go/analysis/passes/errorsas
 golang.org/x/tools/go/analysis/passes/httpresponse
+golang.org/x/tools/go/analysis/passes/ifaceassert
 golang.org/x/tools/go/analysis/passes/inspect
 golang.org/x/tools/go/analysis/passes/internal/analysisutil
 golang.org/x/tools/go/analysis/passes/loopclosure
@@ -67,6 +68,7 @@ golang.org/x/tools/go/analysis/passes/nilfunc
 golang.org/x/tools/go/analysis/passes/printf
 golang.org/x/tools/go/analysis/passes/shift
 golang.org/x/tools/go/analysis/passes/stdmethods
+golang.org/x/tools/go/analysis/passes/stringintconv
 golang.org/x/tools/go/analysis/passes/structtag
 golang.org/x/tools/go/analysis/passes/tests
 golang.org/x/tools/go/analysis/passes/unmarshal
@@ -80,6 +82,5 @@ golang.org/x/tools/go/cfg
 golang.org/x/tools/go/types/objectpath
 golang.org/x/tools/go/types/typeutil
 # golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543
-## explicit
 golang.org/x/xerrors
 golang.org/x/xerrors/internal
diff --git a/src/cmd/vet/main.go b/src/cmd/vet/main.go
index 2a4f929d60..6381de840c 100644
--- a/src/cmd/vet/main.go
+++ b/src/cmd/vet/main.go
@@ -15,12 +15,14 @@ import (
 	"golang.org/x/tools/go/analysis/passes/copylock"
 	"golang.org/x/tools/go/analysis/passes/errorsas"
 	"golang.org/x/tools/go/analysis/passes/httpresponse"
+	"golang.org/x/tools/go/analysis/passes/ifaceassert"
 	"golang.org/x/tools/go/analysis/passes/loopclosure"
 	"golang.org/x/tools/go/analysis/passes/lostcancel"
 	"golang.org/x/tools/go/analysis/passes/nilfunc"
 	"golang.org/x/tools/go/analysis/passes/printf"
 	"golang.org/x/tools/go/analysis/passes/shift"
 	"golang.org/x/tools/go/analysis/passes/stdmethods"
+	"golang.org/x/tools/go/analysis/passes/stringintconv"
 	"golang.org/x/tools/go/analysis/passes/structtag"
 	"golang.org/x/tools/go/analysis/passes/tests"
 	"golang.org/x/tools/go/analysis/passes/unmarshal"
@@ -43,12 +45,14 @@ func main() {
 		copylock.Analyzer,
 		errorsas.Analyzer,
 		httpresponse.Analyzer,
+		ifaceassert.Analyzer,
 		loopclosure.Analyzer,
 		lostcancel.Analyzer,
 		nilfunc.Analyzer,
 		printf.Analyzer,
 		shift.Analyzer,
 		stdmethods.Analyzer,
+		stringintconv.Analyzer,
 		structtag.Analyzer,
 		tests.Analyzer,
 		unmarshal.Analyzer,