feat(AIP-192): Catch unpaired backticks in comments

docs/rules/0192/closed-backticks.md

@@ -0,0 +1,68 @@
+---
+rule:
+  aip: 192
+  name: [core, '0192', closed-backticks]
+  summary: Inline code should be surrounded by backticks.
+permalink: /192/closed-backticks
+redirect_from:
+  - /0192/closed-backticks
+---
+
+# Closed backticks
+
+This rule enforces that any inline code in public comments for proto descriptors
+is surrounded by backticks, as mandated in [AIP-192][].
+
+## Details
+
+This rule looks at each descriptor in each proto file (exempting oneofs and the
+file itself) and complains if _public_ comments include text that only has
+either an opening backtick or a closing backtick.
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+// Incorrect.
+// Fields on the book include:
+//
+// - name`: `string
+message Book {
+  // The resource name of the book.
+  string name = 1;
+}
+```
+
+**Correct** code for this rule:
+
+```proto
+// Correct.
+// Fields on the book include:
+//
+// - `name`: `string`
+message Book {
+  // The resource name of the book.
+  string name = 1;
+}
+```
+
+## Disabling
+
+If you need to violate this rule, use a leading comment above the descriptor.
+Remember to also include an [aip.dev/not-precedent][] comment explaining why.
+
+```proto
+// Fields on the book include:
+//
+// - name`: `string
+// (-- api-linter: core::0192::closed-backticks=disabled
+//     aip.dev/not-precedent: We need to do this because reasons. --)
+message Book {
+  // The resource name of the book.
+  string name = 1;
+}
+```
+
+[aip-192]: https://aip.dev/192
+[aip.dev/not-precedent]: https://aip.dev/not-precedent

rules/aip0192/aip0192.go

@@ -25,6 +25,7 @@ func AddRules(r lint.RuleRegistry) error {
 	return r.Register(
 		192,
 		absoluteLinks,
+		closedBackticks,
 		deprecatedComment,
 		hasComments,
 		noHTML,

rules/aip0192/closed_backticks.go

@@ -0,0 +1,186 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aip0192
+
+import (
+	"regexp"
+	"strings"
+
+	"bitbucket.org/creachadair/stringset"
+	"github.com/googleapis/api-linter/lint"
+	"github.com/googleapis/api-linter/rules/internal/utils"
+	"github.com/jhump/protoreflect/desc"
+)
+
+type backtickPair int
+
+const (
+	unspecified backtickPair = iota
+	missingOpening
+	missingClosing
+	paired
+)
+
+// Represents a backtick character in a line.
+//
+// To narrow which backticks to lint and the likely intended use of a stray
+// backtick, we compute whether the backtick can be used as an opening and/or
+// closing backtick.
+//
+// If the character before a backtick is one of the `separators`, the backtick
+// is considered opening. Likewise, if the character after a backtick is one of
+// the `separators`, the backtick is considered closing.
+type backtick struct {
+	index   int
+	opening bool
+	closing bool
+	pair    backtickPair
+}
+
+var separators = stringset.New(" ", ":", ",", ".", ";", "-")
+var reBacktick = regexp.MustCompile("`")
+
+var closedBackticks = &lint.DescriptorRule{
+	Name: lint.NewRuleName(192, "closed-backticks"),
+	LintDescriptor: func(d desc.Descriptor) []lint.Problem {
+		problems := []lint.Problem{}
+
+		for _, comment := range utils.SeparateInternalComments(d.GetSourceInfo().GetLeadingComments()).External {
+			for _, line := range strings.Split(comment, "\n") {
+				// Pad the line with whitespace, so it's easier to lint
+				// backticks at the start and end of the line.
+				line = " " + line + " "
+
+				// Find all the backticks in the line and compute whether each
+				// one can be used as an opening and/or closing backtick.
+				backticks := []backtick{}
+				for _, loc := range reBacktick.FindAllStringIndex(line, -1) {
+					backticks = append(backticks, backtickAtIndex(line, loc[0]))
+				}
+
+				// Compute whether the backticks are paired.
+				backticks = computeBacktickPairs(filterUnusableBackticks(backticks))
+
+				// Add a problem for each backtick that is missing a pair.
+				for _, backtick := range backticks {
+					if backtick.pair != paired {
+						problems = append(problems, lint.Problem{
+							Message:    "Inline code should be surrounded by backticks.",
+							Suggestion: "`" + suggestionWord(line, backtick) + "`",
+							Descriptor: d,
+						})
+					}
+				}
+			}
+		}
+		return problems
+	},
+}
+
+func backtickAtIndex(line string, index int) backtick {
+	return backtick{
+		index:   index,
+		opening: separators.Contains(string(line[index-1])),
+		closing: separators.Contains(string(line[index+1])),
+	}
+}
+
+// Filter out backticks that cannot be used as opening or closing backticks.
+func filterUnusableBackticks(backticks []backtick) []backtick {
+	list := []backtick{}
+	for _, backtick := range backticks {
+		if backtick.opening || backtick.closing {
+			list = append(list, backtick)
+		}
+	}
+	return list
+}
+
+// Compute whether each backtick is paired with an adjacent backtick.
+//
+// A backtick pair consists of a set of adjacent backticks, where the first is
+// opening and the second is closing. Each backtick can be in at most one pair.
+//
+// This fills in the `pair` field for each backtick. It assumes every backtick
+// is either opening, closing, or both.
+func computeBacktickPairs(backticks []backtick) []backtick {
+	computed := []backtick{}
+
+	prevBacktickOpen := false
+	for i, backtick := range backticks {
+		backtick.pair = computePairState(backtick, prevBacktickOpen)
+
+		// If this backtick got paired, mark the previous one as paired as well.
+		if backtick.pair == paired {
+			computed[i-1].pair = paired
+		}
+
+		// If paired, this backtick cannot be used as an `opening` for another
+		// backtick.
+		prevBacktickOpen = false
+		if backtick.opening && backtick.pair != paired {
+			prevBacktickOpen = true
+		}
+
+		computed = append(computed, backtick)
+	}
+	return computed
+}
+
+func computePairState(backtick backtick, prevBacktickOpen bool) backtickPair {
+	// If the backtick is only opening, it needs a closing backtick.
+	if backtick.opening && !backtick.closing {
+		return missingClosing
+	}
+	// Otherwise, the backtick is closing. It is paired if the last backtick was
+	// opening.
+	if prevBacktickOpen {
+		return paired
+	}
+	return missingOpening
+}
+
+// Extract the word around an unpaired backtick.
+//
+// Even though inline code can include separators (e.g. colons, spaces), just
+// suggest the string of characters up to the first separator character.
+func suggestionWord(line string, backtick backtick) string {
+	switch backtick.pair {
+	case missingOpening:
+		return reverseString(firstWordBeforeSeparator(reverseString(line[:backtick.index])))
+	case missingClosing:
+		return firstWordBeforeSeparator(line[backtick.index+1:])
+	default:
+		return ""
+	}
+}
+
+func firstWordBeforeSeparator(s string) string {
+	index := strings.IndexFunc(s, func(r rune) bool {
+		return separators.Contains(string(r))
+	})
+	if index != -1 {
+		return s[:index]
+	}
+	return s
+}
+
+func reverseString(s string) string {
+	runes := []rune(s)
+	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
+		runes[i], runes[j] = runes[j], runes[i]
+	}
+	return string(runes)
+}

rules/aip0192/closed_backticks_test.go

@@ -0,0 +1,90 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aip0192
+
+import (
+	"testing"
+
+	"github.com/googleapis/api-linter/rules/internal/testutils"
+)
+
+func TestClosedBackticks(t *testing.T) {
+	for _, test := range []struct {
+		name     string
+		Comment  string
+		problems testutils.Problems
+	}{
+		{"ValidWordChars", "`foo_bar_baz_1`", nil},
+		{"MissingFrontBacktickWordChars", "foo_bar_baz_1`", testutils.Problems{{Suggestion: "`foo_bar_baz_1`"}}},
+		{"MissingBackBacktickWordChars", "`foo_bar_baz_1", testutils.Problems{{Suggestion: "`foo_bar_baz_1`"}}},
+
+		{"ValidBetweenWords", "foo `bar` baz", nil},
+		{"MissingFrontBacktickBetweenWords", "foo bar` baz", testutils.Problems{{Suggestion: "`bar`"}}},
+		{"MissingBackBacktickBetweenWords", "foo `bar baz", testutils.Problems{{Suggestion: "`bar`"}}},
+
+		{"ValidNonWordChars", "`foo:bar/baz->qux.quux[0]()`", nil},
+		{"MissingFrontBacktickNonWordChars", "foo:bar/baz->qux.quux[0]()`", testutils.Problems{{Suggestion: "`quux[0]()`"}}},
+		{"MissingBackBacktickNonWordChars", "`foo:bar/baz->qux.quux[0]()", testutils.Problems{{Suggestion: "`foo`"}}},
+
+		{"ValidContainsSpace", "`foo + bar`", nil},
+		{"MissingFrontBacktickContainsSpace", "foo + bar`", testutils.Problems{{Suggestion: "`bar`"}}},
+		{"MissingBackBacktickContainsSpace", "`foo + bar", testutils.Problems{{Suggestion: "`foo`"}}},
+
+		{"ValidNonAscii", "`汉语`", nil},
+		{"MissingFrontBacktickNonAscii", "汉语`", testutils.Problems{{Suggestion: "`汉语`"}}},
+		{"MissingBackBacktickNonAscii", "`汉语", testutils.Problems{{Suggestion: "`汉语`"}}},
+
+		{"ValidQuotes", "`\"foo\"`", nil},
+		{"MissingFrontBacktickQuotes", "\"foo\"`", testutils.Problems{{Suggestion: "`\"foo\"`"}}},
+		{"MissingBackBacktickQuotes", "`\"foo\"", testutils.Problems{{Suggestion: "`\"foo\"`"}}},
+
+		{"ValidSeparatedByColons", "foo:`bar:baz`:qux", nil},
+		{"MissingFrontBacktickSeparatedByColons", "foo:`bar:baz:qux", testutils.Problems{{Suggestion: "`bar`"}}},
+		{"MissingBackBacktickSeparatedByColons", "foo:bar:baz`:qux", testutils.Problems{{Suggestion: "`baz`"}}},
+
+		{"ValidComma", "`name`, a string", nil},
+		{"MissingFrontBacktickComma", "name`, a string", testutils.Problems{{Suggestion: "`name`"}}},
+		{"MissingBackBacktickComma", "`name, a string", testutils.Problems{{Suggestion: "`name`"}}},
+
+		{"ValidMultipleCodeText", "`name`: `string`", nil},
+		{"MissingFrontBacktickMultipleCodeText", "name`: string`", testutils.Problems{{Suggestion: "`name`"}, {Suggestion: "`string`"}}},
+		{"MissingBackBacktickMultipleCodeText", "`name: `string", testutils.Problems{{Suggestion: "`name`"}, {Suggestion: "`string`"}}},
+		{"MissingFrontAndBackBacktickMultipleCodeText", "name`: `string", testutils.Problems{{Suggestion: "`name`"}, {Suggestion: "`string`"}}},
+
+		{"ValidContainsColon", "`name: string`", nil},
+
+		{"ValidContainsSeparator", "`.`", nil},
+		{"MissingFrontBacktickContainsSeparator", ".`", testutils.Problems{{Suggestion: "``"}}},
+		{"MissingBackBacktickContainsSeparator", "`.", testutils.Problems{{Suggestion: "``"}}},
+
+		{"ValidEmptySpace", "``", nil},
+		{"ValidEmptySpaces", "`` ``", nil},
+		{"UnpairedEmptySpace", "`` `", testutils.Problems{{Suggestion: "``"}}},
+
+		{"IgnoreTripleBacktick", "```", nil},
+		{"IgnoreBackticksWithinWords", "a`b`c`d", nil},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			f := testutils.ParseProto3Tmpl(t, `
+			  // {{.Comment}}
+			  message Foo {}
+			`, test)
+			m := f.GetMessageTypes()[0]
+			if diff := test.problems.SetDescriptor(m).Diff(closedBackticks.Lint(f)); diff != "" {
+				t.Errorf(diff)
+			}
+		})
+	}
+}