go/doc/comment: parse and print identifiers, automatic links

[This CL is part of a sequence implementing the proposal #51082.
The design doc is at https://go.dev/s/godocfmt-design.]

Implement parsing and printing of unmarked identifiers
and automatic URL links in plain text.

For #51082.

Change-Id: Ib83ad482937501a6fc14fa788eab289533a68e3a
Reviewed-on: https://go-review.googlesource.com/c/go/+/397280
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/go/doc/comment/html.go

@@ -44,6 +44,16 @@ func (p *htmlPrinter) text(out *bytes.Buffer, x []Text) {
 		switch t := t.(type) {
 		case Plain:
 			p.escape(out, string(t))
+		case Italic:
+			out.WriteString("<i>")
+			p.escape(out, string(t))
+			out.WriteString("</i>")
+		case *Link:
+			out.WriteString(`<a href="`)
+			p.escape(out, t.URL)
+			out.WriteString(`">`)
+			p.text(out, t.Text)
+			out.WriteString("</a>")
 		}
 	}
 }

src/go/doc/comment/markdown.go

@@ -77,6 +77,16 @@ func (p *mdPrinter) rawText(out *bytes.Buffer, x []Text) {
 		switch t := t.(type) {
 		case Plain:
 			p.escape(out, string(t))
+		case Italic:
+			out.WriteString("*")
+			p.escape(out, string(t))
+			out.WriteString("*")
+		case *Link:
+			out.WriteString("[")
+			p.rawText(out, t.Text)
+			out.WriteString("](")
+			out.WriteString(t.URL)
+			out.WriteString(")")
 		}
 	}
 }

src/go/doc/comment/parse.go

@@ -261,7 +261,12 @@ func (p *Parser) Parse(text string) *Doc {
 	}
 
 	// Second pass: interpret all the Plain text now that we know the links.
-	// TODO: Actually interpret the plain text.
+	for _, b := range d.Content {
+		switch b := b.(type) {
+		case *Paragraph:
+			b.Text = d.parseText(string(b.Text[0].(Plain)))
+		}
+	}
 
 	return d.Doc
 }
@@ -401,6 +406,74 @@ func (d *parseDoc) paragraph(lines []string) (b Block, rest []string) {
 	return &Paragraph{Text: []Text{Plain(strings.Join(lines, "\n"))}}, rest
 }
 
+// parseText parses s as text and returns the parsed Text elements.
+func (d *parseDoc) parseText(s string) []Text {
+	var out []Text
+	var w strings.Builder
+	wrote := 0
+	writeUntil := func(i int) {
+		w.WriteString(s[wrote:i])
+		wrote = i
+	}
+	flush := func(i int) {
+		writeUntil(i)
+		if w.Len() > 0 {
+			out = append(out, Plain(w.String()))
+			w.Reset()
+		}
+	}
+	for i := 0; i < len(s); {
+		t := s[i:]
+		const autoLink = true
+		if autoLink {
+			if url, ok := autoURL(t); ok {
+				flush(i)
+				// Note: The old comment parser would look up the URL in words
+				// and replace the target with words[URL] if it was non-empty.
+				// That would allow creating links that display as one URL but
+				// when clicked go to a different URL. Not sure what the point
+				// of that is, so we're not doing that lookup here.
+				out = append(out, &Link{Auto: true, Text: []Text{Plain(url)}, URL: url})
+				i += len(url)
+				wrote = i
+				continue
+			}
+			if id, ok := ident(t); ok {
+				url, italics := d.Words[id]
+				if !italics {
+					i += len(id)
+					continue
+				}
+				flush(i)
+				if url == "" {
+					out = append(out, Italic(id))
+				} else {
+					out = append(out, &Link{Auto: true, Text: []Text{Italic(id)}, URL: url})
+				}
+				i += len(id)
+				wrote = i
+				continue
+			}
+		}
+		switch {
+		case strings.HasPrefix(t, "``"):
+			writeUntil(i)
+			w.WriteRune('“')
+			i += 2
+			wrote = i
+		case strings.HasPrefix(t, "''"):
+			writeUntil(i)
+			w.WriteRune('”')
+			i += 2
+			wrote = i
+		default:
+			i++
+		}
+	}
+	flush(len(s))
+	return out
+}
+
 // autoURL checks whether s begins with a URL that should be hyperlinked.
 // If so, it returns the URL, which is a prefix of s, and ok == true.
 // Otherwise it returns "", false.

src/go/doc/comment/print.go

@@ -103,6 +103,10 @@ func (p *commentPrinter) text(out *bytes.Buffer, indent string, x []Text) {
 		switch t := t.(type) {
 		case Plain:
 			p.indent(out, indent, string(t))
+		case Italic:
+			p.indent(out, indent, string(t))
+		case *Link:
+			p.text(out, indent, t.Text)
 		}
 	}
 }

src/go/doc/comment/testdata/hello.txt

@@ -30,8 +30,6 @@ Hello, world
 
 This is a test.
 -- text --
-Hello,
-world
+Hello, world
 
-This is
-a test.
+This is a test.

src/go/doc/comment/testdata/link.txt

@@ -0,0 +1,17 @@
+-- input --
+The Go home page is https://go.dev/.
+It used to be https://golang.org.
+
+-- gofmt --
+The Go home page is https://go.dev/.
+It used to be https://golang.org.
+
+-- text --
+The Go home page is https://go.dev/. It used to be https://golang.org.
+
+-- markdown --
+The Go home page is [https://go.dev/](https://go.dev/). It used to be [https://golang.org](https://golang.org).
+
+-- html --
+<p>The Go home page is <a href="https://go.dev/">https://go.dev/</a>.
+It used to be <a href="https://golang.org">https://golang.org</a>.

src/go/doc/comment/testdata/para.txt

@@ -0,0 +1,17 @@
+-- input --
+Hello, world.
+This is a paragraph.
+
+-- gofmt --
+Hello, world.
+This is a paragraph.
+
+-- text --
+Hello, world. This is a paragraph.
+
+-- markdown --
+Hello, world. This is a paragraph.
+
+-- html --
+<p>Hello, world.
+This is a paragraph.

src/go/doc/comment/testdata/text2.txt

@@ -0,0 +1,14 @@
+{"TextWidth": -1}
+-- input --
+Package gob manages streams of gobs - binary values exchanged between an
+Encoder (transmitter) and a Decoder (receiver). A typical use is
+transporting arguments and results of remote procedure calls (RPCs) such as
+those provided by package "net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream
+and is most efficient when a single Encoder is used to transmit a stream of
+values, amortizing the cost of compilation.
+-- text --
+Package gob manages streams of gobs - binary values exchanged between an Encoder (transmitter) and a Decoder (receiver). A typical use is transporting arguments and results of remote procedure calls (RPCs) such as those provided by package "net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream and is most efficient when a single Encoder is used to transmit a stream of values, amortizing the cost of compilation.

src/go/doc/comment/testdata/words.txt

@@ -0,0 +1,10 @@
+-- input --
+This is an italicword and a linkedword and Unicöde.
+-- gofmt --
+This is an italicword and a linkedword and Unicöde.
+-- text --
+This is an italicword and a linkedword and Unicöde.
+-- markdown --
+This is an *italicword* and a [*linkedword*](https://example.com/linkedword) and Unicöde.
+-- html --
+<p>This is an <i>italicword</i> and a <a href="https://example.com/linkedword"><i>linkedword</i></a> and Unicöde.

src/go/doc/comment/testdata_test.go

@@ -6,6 +6,7 @@ package comment
 
 import (
 	"bytes"
+	"encoding/json"
 	"fmt"
 	"internal/diff"
 	"internal/txtar"
@@ -20,6 +21,10 @@ func TestTestdata(t *testing.T) {
 		t.Fatalf("no testdata")
 	}
 	var p Parser
+	p.Words = map[string]string{
+		"italicword": "",
+		"linkedword": "https://example.com/linkedword",
+	}
 
 	stripDollars := func(b []byte) []byte {
 		// Remove trailing $ on lines.
@@ -30,10 +35,17 @@ func TestTestdata(t *testing.T) {
 	}
 	for _, file := range files {
 		t.Run(filepath.Base(file), func(t *testing.T) {
+			var pr Printer
 			a, err := txtar.ParseFile(file)
 			if err != nil {
 				t.Fatal(err)
 			}
+			if len(a.Comment) > 0 {
+				err := json.Unmarshal(a.Comment, &pr)
+				if err != nil {
+					t.Fatalf("unmarshalling top json: %v", err)
+				}
+			}
 			if len(a.Files) < 1 || a.Files[0].Name != "input" {
 				t.Fatalf("first file is not %q", "input")
 			}
@@ -44,7 +56,6 @@ func TestTestdata(t *testing.T) {
 					want = want[:len(want)-1]
 				}
 				var out []byte
-				var pr Printer
 				switch f.Name {
 				default:
 					t.Fatalf("unknown output file %q", f.Name)

src/go/doc/comment/text.go

@@ -7,11 +7,13 @@ package comment
 import (
 	"bytes"
 	"fmt"
+	"strings"
 )
 
 // A textPrinter holds the state needed for printing a Doc as plain text.
 type textPrinter struct {
 	*Printer
+	long bytes.Buffer
 }
 
 // Text returns a textual formatting of the Doc.
@@ -59,11 +61,23 @@ func (p *textPrinter) block(out *bytes.Buffer, x Block) {
 // text prints the text sequence x to out.
 // TODO: Wrap lines.
 func (p *textPrinter) text(out *bytes.Buffer, x []Text) {
+	p.oneLongLine(&p.long, x)
+	out.WriteString(strings.ReplaceAll(p.long.String(), "\n", " "))
+	p.long.Reset()
+	writeNL(out)
+}
+
+// oneLongLine prints the text sequence x to out as one long line,
+// without worrying about line wrapping.
+func (p *textPrinter) oneLongLine(out *bytes.Buffer, x []Text) {
 	for _, t := range x {
 		switch t := t.(type) {
 		case Plain:
 			out.WriteString(string(t))
+		case Italic:
+			out.WriteString(string(t))
+		case *Link:
+			p.oneLongLine(out, t.Text)
 		}
 	}
-	writeNL(out)
 }