gopls/test: it is safe to ignore json unmarshalling errors

This test checks that if a single value in the Initialize message
changes, the resulting unmarshalled struct changes in no more than
one place. The implication is that ignoring UnmarshalTypeErrors
in LSP processing is safer than causing a fatal error, which is the
current state.

Change-Id: I64bbf6f785c32fa7483966a117ac3b6f11d573be
Reviewed-on: https://go-review.googlesource.com/c/tools/+/310109
Run-TryBot: Peter Weinberger <pjw@google.com>
Trust: Peter Weinberger <pjw@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

gopls/go.mod

@@ -3,6 +3,7 @@ module golang.org/x/tools/gopls
 go 1.12
 
 require (
+	github.com/google/go-cmp v0.5.5
 	github.com/jba/templatecheck v0.5.0
 	github.com/sanity-io/litter v1.5.0
 	github.com/sergi/go-diff v1.1.0

gopls/go.sum

@@ -4,8 +4,9 @@ github.com/davecgh/go-spew v0.0.0-20161028175848-04cdfd42973b/go.mod h1:J7Y8YcW2
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/google/go-cmp v0.5.4 h1:L8R9j+yAqZuZjsqh/z+F1NCffTKKLShY6zXTItVIZ8M=
 github.com/google/go-cmp v0.5.4/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/safehtml v0.0.2 h1:ZOt2VXg4x24bW0m2jtzAOkhoXV0iM8vNKc0paByCZqM=
 github.com/google/safehtml v0.0.2/go.mod h1:L4KWwDsUJdECRAEpZoBn3O64bQaywRscowZjJAzjHnU=
 github.com/jba/templatecheck v0.5.0 h1:sZwNjXG3xNApuwKmgUWEo2JuxmG0sgNaELl0zwRQ9x8=

gopls/test/json_test.go

@@ -0,0 +1,134 @@
+// Copyright 2021 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 gopls_test
+
+import (
+	"encoding/json"
+	"fmt"
+	"regexp"
+	"strings"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"golang.org/x/tools/internal/lsp/protocol"
+)
+
+// verify that type errors in Initialize lsp messages don't cause
+// any other unmarshalling errors. The code looks at single values and the
+// first component of array values. Each occurrence is replaced by something
+// of a different type,  the resulting string unmarshalled, and compared to
+// the unmarshalling of the unchanged strings. The test passes if there is no
+// more than a single difference reported. That is, if changing a single value
+// in the message changes no more than a single value in the unmarshalled struct,
+// it is safe to ignore *json.UnmarshalTypeError.
+
+// strings are changed to numbers or bools (true)
+// bools are changed to numbers or strings
+// numbers are changed to strings or bools
+
+// a recent Initialize message taken from a log
+const input = `{"processId":38349,"clientInfo":{"name":"vscode","version":"1.56.0-insider"},"rootPath":"/Users/pjw/latest/tools","rootUri":"file:///Users/pjw/latest/tools","capabilities":{"workspace":{"applyEdit":true,"workspaceEdit":{"documentChanges":true,"resourceOperations":["create","rename","delete"],"failureHandling":"textOnlyTransactional"},"didChangeConfiguration":{"dynamicRegistration":true},"didChangeWatchedFiles":{"dynamicRegistration":true},"symbol":{"dynamicRegistration":true,"symbolKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]},"tagSupport":{"valueSet":[1]}},"executeCommand":{"dynamicRegistration":true},"configuration":true,"workspaceFolders":true,"semanticTokens":{"refreshSupport":true}},"textDocument":{"publishDiagnostics":{"relatedInformation":true,"versionSupport":false,"tagSupport":{"valueSet":[1,2]},"codeDescriptionSupport":true,"dataSupport":true},"synchronization":{"dynamicRegistration":true,"willSave":true,"willSaveWaitUntil":true,"didSave":true},"completion":{"dynamicRegistration":true,"contextSupport":true,"completionItem":{"snippetSupport":true,"commitCharactersSupport":true,"documentationFormat":["markdown","plaintext"],"deprecatedSupport":true,"preselectSupport":true,"tagSupport":{"valueSet":[1]},"insertReplaceSupport":true,"resolveSupport":{"properties":["documentation","detail","additionalTextEdits"]}},"completionItemKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]}},"hover":{"dynamicRegistration":true,"contentFormat":["markdown","plaintext"]},"signatureHelp":{"dynamicRegistration":true,"signatureInformation":{"documentationFormat":["markdown","plaintext"],"parameterInformation":{"labelOffsetSupport":true},"activeParameterSupport":true},"contextSupport":true},"definition":{"dynamicRegistration":true,"linkSupport":true},"references":{"dynamicRegistration":true},"documentHighlight":{"dynamicRegistration":true},"documentSymbol":{"dynamicRegistration":true,"symbolKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]},"hierarchicalDocumentSymbolSupport":true,"tagSupport":{"valueSet":[1]},"labelSupport":true},"codeAction":{"dynamicRegistration":true,"isPreferredSupport":true,"disabledSupport":true,"dataSupport":true,"resolveSupport":{"properties":["edit"]},"codeActionLiteralSupport":{"codeActionKind":{"valueSet":["","quickfix","refactor","refactor.extract","refactor.inline","refactor.rewrite","source","source.organizeImports"]}}},"codeLens":{"dynamicRegistration":true},"formatting":{"dynamicRegistration":true},"rangeFormatting":{"dynamicRegistration":true},"onTypeFormatting":{"dynamicRegistration":true},"rename":{"dynamicRegistration":true,"prepareSupport":true,"prepareSupportDefaultBehavior":true},"documentLink":{"dynamicRegistration":true,"tooltipSupport":true},"typeDefinition":{"dynamicRegistration":true,"linkSupport":true},"implementation":{"dynamicRegistration":true,"linkSupport":true},"colorProvider":{"dynamicRegistration":true},"foldingRange":{"dynamicRegistration":true,"rangeLimit":5000,"lineFoldingOnly":true},"declaration":{"dynamicRegistration":true,"linkSupport":true},"selectionRange":{"dynamicRegistration":true},"callHierarchy":{"dynamicRegistration":true},"semanticTokens":{"dynamicRegistration":true,"tokenTypes":["namespace","type","class","enum","interface","struct","typeParameter","parameter","variable","property","enumMember","event","function","member","macro","keyword","modifier","comment","string","number","regexp","operator"],"tokenModifiers":["declaration","definition","readonly","static","deprecated","abstract","async","modification","documentation","defaultLibrary"],"formats":["relative"],"requests":{"range":true,"full":{"delta":true}}}},"window":{"workDoneProgress":true}},"initializationOptions":{"usePlaceholders":true,"completionDocumentation":true,"verboseOutput":false,"codelenses":{"gc_details":true},"analyses":{"fillstruct":true,"staticcheck":true},"experimentalWorkspaceModule":true,"semanticTokens":true},"trace":"off","workspaceFolders":[{"uri":"file:///Users/pjw/latest/tools","name":"tools"}]}`
+
+type DiffReporter struct {
+	path  cmp.Path
+	diffs []string
+}
+
+func (r *DiffReporter) PushStep(ps cmp.PathStep) {
+	r.path = append(r.path, ps)
+}
+
+func (r *DiffReporter) Report(rs cmp.Result) {
+	if !rs.Equal() {
+		vx, vy := r.path.Last().Values()
+		r.diffs = append(r.diffs, fmt.Sprintf("%#v:\n\t-: %+v\n\t+: %+v\n", r.path, vx, vy))
+	}
+}
+
+func (r *DiffReporter) PopStep() {
+	r.path = r.path[:len(r.path)-1]
+}
+
+func (r *DiffReporter) String() string {
+	return strings.Join(r.diffs, "\n")
+}
+
+func TestStringChanges(t *testing.T) {
+	// string as value
+	stringLeaf := regexp.MustCompile(`:("[^"]*")`)
+	leafs := stringLeaf.FindAllStringSubmatchIndex(input, -1)
+	allDeltas(t, leafs, "23", "true")
+	// string as first element of array
+	stringArray := regexp.MustCompile(`[[]("[^"]*")`)
+	arrays := stringArray.FindAllStringSubmatchIndex(input, -1)
+	allDeltas(t, arrays, "23", "true")
+}
+
+func TestBoolChanges(t *testing.T) {
+	boolLeaf := regexp.MustCompile(`:(true|false)(,|})`)
+	leafs := boolLeaf.FindAllStringSubmatchIndex(input, -1)
+	allDeltas(t, leafs, "23", `"xx"`)
+	boolArray := regexp.MustCompile(`:[[](true|false)(,|])`)
+	arrays := boolArray.FindAllStringSubmatchIndex(input, -1)
+	allDeltas(t, arrays, "23", `"xx"`)
+}
+
+func TestNumberChanges(t *testing.T) {
+	numLeaf := regexp.MustCompile(`:(\d+)(,|})`)
+	leafs := numLeaf.FindAllStringSubmatchIndex(input, -1)
+	allDeltas(t, leafs, "true", `"xx"`)
+	numArray := regexp.MustCompile(`:[[](\d+)(,|])`)
+	arrays := numArray.FindAllStringSubmatchIndex(input, -1)
+	allDeltas(t, arrays, "true", `"xx"`)
+}
+
+// v is a set of matches. check that substituting any repl never
+// creates more than 1 unmarshaling error
+func allDeltas(t *testing.T, v [][]int, repls ...string) {
+	t.Helper()
+	for _, repl := range repls {
+		for i, x := range v {
+			err := tryChange(x[2], x[3], repl)
+			if err != nil {
+				t.Errorf("%d:%q %v", i, input[x[2]:x[3]], err)
+			}
+		}
+	}
+}
+
+func tryChange(start, end int, repl string) error {
+	var p, q protocol.InitializeParams
+	mod := input[:start] + repl + input[end:]
+	excerpt := func() (string, string) {
+		a := start - 5
+		if a < 0 {
+			a = 0
+		}
+		b := end + 5
+		if b > len(input) {
+			// trusting repl to be no longer than what it replaces
+			b = len(input)
+		}
+		ma := input[a:b]
+		mb := mod[a:b]
+		return ma, mb
+	}
+	if err := json.Unmarshal([]byte(input), &p); err != nil {
+		return fmt.Errorf("%s %v", repl, err)
+	}
+	if err := json.Unmarshal([]byte(mod), &q); err == nil {
+		return nil // no errors is ok
+	} else if _, ok := err.(*json.UnmarshalTypeError); !ok {
+		return fmt.Errorf("%T, not *json.UnmarshalTypeError", err)
+	}
+
+	var r DiffReporter
+	cmp.Diff(p, q, cmp.Reporter(&r))
+	if len(r.diffs) > 1 { // 0 is possible, e.g., for interface{}
+		ma, mb := excerpt()
+		return fmt.Errorf("got %d diffs for %q\n%s\n%s", len(r.diffs), repl, ma, mb)
+	}
+	return nil
+}