cmd/go, go/build: parse directives in file headers

For #56986, go/build needs to report up to cmd/go
about //go:debug lines found in the source code.
Rather than make a special case for //go:debug,
this change gathers all top-level directives above the
package line and includes them in the result.

The go command's module index must match go/build,
so this CL contains the code to update the index as well.

A future CL will use the //go:debug lines to prepare the default
GODEBUG settings, as well as rejecting such lines in non-main
packages.

Change-Id: I66ab8dc72f9cd65c503b10b744367caca233f8a6
Reviewed-on: https://go-review.googlesource.com/c/go/+/453603
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

api/next/56986.txt

@@ -0,0 +1,6 @@
+pkg go/build, type Directive struct #56986
+pkg go/build, type Directive struct, Pos token.Position #56986
+pkg go/build, type Directive struct, Text string #56986
+pkg go/build, type Package struct, Directives []Directive #56986
+pkg go/build, type Package struct, TestDirectives []Directive #56986
+pkg go/build, type Package struct, XTestDirectives []Directive #56986

src/cmd/go/internal/load/pkg.go

@@ -230,6 +230,9 @@ type PackageInternal struct {
 	TestmainGo        *[]byte              // content for _testmain.go
 	Embed             map[string][]string  // //go:embed comment mapping
 	OrigImportPath    string               // original import path before adding '_test' suffix
+	Directives        []build.Directive
+	TestDirectives    []build.Directive
+	XTestDirectives   []build.Directive
 
 	Asmflags   []string // -asmflags for this package
 	Gcflags    []string // -gcflags for this package
@@ -435,6 +438,9 @@ func (p *Package) copyBuild(opts PackageOpts, pp *build.Package) {
 	p.TestEmbedPatterns = pp.TestEmbedPatterns
 	p.XTestEmbedPatterns = pp.XTestEmbedPatterns
 	p.Internal.OrigImportPath = pp.ImportPath
+	p.Internal.Directives = pp.Directives
+	p.Internal.TestDirectives = pp.TestDirectives
+	p.Internal.XTestDirectives = pp.XTestDirectives
 }
 
 // A PackageError describes an error loading information about a package.

src/cmd/go/internal/modindex/build.go

@@ -383,6 +383,7 @@ type fileInfo struct {
 	parseErr   error
 	imports    []fileImport
 	embeds     []fileEmbed
+	directives []build.Directive
 
 	// Additional fields added to go/build's fileinfo for the purposes of the modindex package.
 	binaryOnly           bool

src/cmd/go/internal/modindex/build_read.go

@@ -13,6 +13,7 @@ import (
 	"errors"
 	"fmt"
 	"go/ast"
+	"go/build"
 	"go/parser"
 	"go/token"
 	"io"
@@ -474,6 +475,18 @@ func readGoInfo(f io.Reader, info *fileInfo) error {
 		}
 	}
 
+	// Extract directives.
+	for _, group := range info.parsed.Comments {
+		if group.Pos() >= info.parsed.Package {
+			break
+		}
+		for _, c := range group.List {
+			if strings.HasPrefix(c.Text, "//go:") {
+				info.directives = append(info.directives, build.Directive{Text: c.Text, Pos: info.fset.Position(c.Slash)})
+			}
+		}
+	}
+
 	// If the file imports "embed",
 	// we have to look for //go:embed comments
 	// in the remainder of the file.

src/cmd/go/internal/modindex/read.go

@@ -580,6 +580,7 @@ func (rp *IndexPackage) Import(bctxt build.Context, mode build.ImportMode) (p *b
 
 		var fileList *[]string
 		var importMap, embedMap map[string][]token.Position
+		var directives *[]build.Directive
 		switch {
 		case isCgo:
 			allTags["cgo"] = true
@@ -587,6 +588,7 @@ func (rp *IndexPackage) Import(bctxt build.Context, mode build.ImportMode) (p *b
 				fileList = &p.CgoFiles
 				importMap = importPos
 				embedMap = embedPos
+				directives = &p.Directives
 			} else {
 				// Ignore Imports and Embeds from cgo files if cgo is disabled.
 				fileList = &p.IgnoredGoFiles
@@ -595,14 +597,17 @@ func (rp *IndexPackage) Import(bctxt build.Context, mode build.ImportMode) (p *b
 			fileList = &p.XTestGoFiles
 			importMap = xTestImportPos
 			embedMap = xTestEmbedPos
+			directives = &p.XTestDirectives
 		case isTest:
 			fileList = &p.TestGoFiles
 			importMap = testImportPos
 			embedMap = testEmbedPos
+			directives = &p.TestDirectives
 		default:
 			fileList = &p.GoFiles
 			importMap = importPos
 			embedMap = embedPos
+			directives = &p.Directives
 		}
 		*fileList = append(*fileList, name)
 		if importMap != nil {
@@ -615,6 +620,9 @@ func (rp *IndexPackage) Import(bctxt build.Context, mode build.ImportMode) (p *b
 				embedMap[e.pattern] = append(embedMap[e.pattern], e.position)
 			}
 		}
+		if directives != nil {
+			*directives = append(*directives, tf.directives()...)
+		}
 	}
 
 	p.EmbedPatterns, p.EmbedPatternPos = cleanDecls(embedPos)
@@ -902,6 +910,13 @@ func (sf *sourceFile) embedsOffset() int {
 	return pos + 4 + n*(4*5)
 }
 
+func (sf *sourceFile) directivesOffset() int {
+	pos := sf.embedsOffset()
+	n := sf.d.intAt(pos)
+	// each import is 5 uint32s (string + tokpos)
+	return pos + 4 + n*(4*5)
+}
+
 func (sf *sourceFile) imports() []rawImport {
 	sf.onceReadImports.Do(func() {
 		importsOffset := sf.importsOffset()
@@ -927,6 +942,17 @@ func (sf *sourceFile) embeds() []embed {
 	return ret
 }
 
+func (sf *sourceFile) directives() []build.Directive {
+	directivesOffset := sf.directivesOffset()
+	r := sf.d.readAt(directivesOffset)
+	numDirectives := r.int()
+	ret := make([]build.Directive, numDirectives)
+	for i := range ret {
+		ret[i] = build.Directive{Text: r.string(), Pos: r.tokpos()}
+	}
+	return ret
+}
+
 func asString(b []byte) string {
 	return unsafe.String(unsafe.SliceData(b), len(b))
 }

src/cmd/go/internal/modindex/scan.go

@@ -11,6 +11,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"go/build"
 	"go/doc"
 	"go/scanner"
 	"go/token"
@@ -159,6 +160,7 @@ type rawFile struct {
 	plusBuildConstraints []string
 	imports              []rawImport
 	embeds               []embed
+	directives           []build.Directive
 }
 
 type rawImport struct {
@@ -231,6 +233,7 @@ func importRaw(modroot, reldir string) *rawPackage {
 			goBuildConstraint:    info.goBuildConstraint,
 			plusBuildConstraints: info.plusBuildConstraints,
 			binaryOnly:           info.binaryOnly,
+			directives:           info.directives,
 		}
 		if info.parsed != nil {
 			rf.pkgName = info.parsed.Name.Name

src/cmd/go/internal/modindex/write.go

@@ -11,7 +11,7 @@ import (
 	"sort"
 )
 
-const indexVersion = "go index v1" // 11 bytes (plus \n), to align uint32s in index
+const indexVersion = "go index v2" // 11 bytes (plus \n), to align uint32s in index
 
 // encodeModuleBytes produces the encoded representation of the module index.
 // encodeModuleBytes may modify the packages slice.
@@ -84,6 +84,12 @@ func encodeFile(e *encoder, f *rawFile) {
 		e.String(embed.pattern)
 		e.Position(embed.position)
 	}
+
+	e.Int(len(f.directives))
+	for _, d := range f.directives {
+		e.String(d.Text)
+		e.Position(d.Pos)
+	}
 }
 
 func newEncoder() *encoder {

src/go/build/build.go

@@ -455,6 +455,11 @@ type Package struct {
 	TestGoFiles  []string // _test.go files in package
 	XTestGoFiles []string // _test.go files outside package
 
+	// Go directive comments (//go:zzz...) found in source files.
+	Directives      []Directive
+	TestDirectives  []Directive
+	XTestDirectives []Directive
+
 	// Dependency information
 	Imports        []string                    // import paths from GoFiles, CgoFiles
 	ImportPos      map[string][]token.Position // line information for Imports
@@ -476,6 +481,12 @@ type Package struct {
 	XTestEmbedPatternPos map[string][]token.Position // line information for XTestEmbedPatternPos
 }
 
+// A Directive is a Go directive comment (//go:zzz...) found in a source file.
+type Directive struct {
+	Text string         // full line comment including leading slashes
+	Pos  token.Position // position of comment
+}
+
 // IsCommand reports whether the package is considered a
 // command to be installed (not just a library).
 // Packages named "main" are treated as commands.
@@ -969,6 +980,7 @@ Found:
 
 		var fileList *[]string
 		var importMap, embedMap map[string][]token.Position
+		var directives *[]Directive
 		switch {
 		case isCgo:
 			allTags["cgo"] = true
@@ -976,6 +988,7 @@ Found:
 				fileList = &p.CgoFiles
 				importMap = importPos
 				embedMap = embedPos
+				directives = &p.Directives
 			} else {
 				// Ignore imports and embeds from cgo files if cgo is disabled.
 				fileList = &p.IgnoredGoFiles
@@ -984,14 +997,17 @@ Found:
 			fileList = &p.XTestGoFiles
 			importMap = xTestImportPos
 			embedMap = xTestEmbedPos
+			directives = &p.XTestDirectives
 		case isTest:
 			fileList = &p.TestGoFiles
 			importMap = testImportPos
 			embedMap = testEmbedPos
+			directives = &p.TestDirectives
 		default:
 			fileList = &p.GoFiles
 			importMap = importPos
 			embedMap = embedPos
+			directives = &p.Directives
 		}
 		*fileList = append(*fileList, name)
 		if importMap != nil {
@@ -1004,6 +1020,9 @@ Found:
 				embedMap[emb.pattern] = append(embedMap[emb.pattern], emb.pos)
 			}
 		}
+		if directives != nil {
+			*directives = append(*directives, info.directives...)
+		}
 	}
 
 	for tag := range allTags {
@@ -1390,6 +1409,7 @@ type fileInfo struct {
 	parseErr   error
 	imports    []fileImport
 	embeds     []fileEmbed
+	directives []Directive
 }
 
 type fileImport struct {

src/go/build/build_test.go

@@ -5,6 +5,7 @@
 package build
 
 import (
+	"fmt"
 	"internal/testenv"
 	"io"
 	"os"
@@ -801,3 +802,27 @@ func TestAllTagsNonSourceFile(t *testing.T) {
 		t.Errorf("AllTags = %v, want empty", p.AllTags)
 	}
 }
+
+func TestDirectives(t *testing.T) {
+	p, err := ImportDir("testdata/directives", 0)
+	if err != nil {
+		t.Fatalf("could not import testdata: %v", err)
+	}
+
+	check := func(name string, list []Directive, want string) {
+		if runtime.GOOS == "windows" {
+			want = strings.ReplaceAll(want, "testdata/directives/", `testdata\\directives\\`)
+		}
+		t.Helper()
+		s := fmt.Sprintf("%q", list)
+		if s != want {
+			t.Errorf("%s = %s, want %s", name, s, want)
+		}
+	}
+	check("Directives", p.Directives,
+		`[{"//go:main1" "testdata/directives/a.go:1:1"} {"//go:plant" "testdata/directives/eve.go:1:1"}]`)
+	check("TestDirectives", p.TestDirectives,
+		`[{"//go:test1" "testdata/directives/a_test.go:1:1"} {"//go:test2" "testdata/directives/b_test.go:1:1"}]`)
+	check("XTestDirectives", p.XTestDirectives,
+		`[{"//go:xtest1" "testdata/directives/c_test.go:1:1"} {"//go:xtest2" "testdata/directives/d_test.go:1:1"} {"//go:xtest3" "testdata/directives/d_test.go:2:1"}]`)
+}

src/go/build/read.go

@@ -471,6 +471,18 @@ func readGoInfo(f io.Reader, info *fileInfo) error {
 		}
 	}
 
+	// Extract directives.
+	for _, group := range info.parsed.Comments {
+		if group.Pos() >= info.parsed.Package {
+			break
+		}
+		for _, c := range group.List {
+			if strings.HasPrefix(c.Text, "//go:") {
+				info.directives = append(info.directives, Directive{c.Text, info.fset.Position(c.Slash)})
+			}
+		}
+	}
+
 	// If the file imports "embed",
 	// we have to look for //go:embed comments
 	// in the remainder of the file.

src/go/build/testdata/directives/a.go

@@ -0,0 +1,3 @@
+//go:main1
+
+package p

src/go/build/testdata/directives/a_test.go

@@ -0,0 +1,3 @@
+//go:test1
+
+package p

src/go/build/testdata/directives/b_test.go

@@ -0,0 +1,5 @@
+//go:test2
+
+package p
+
+//go:ignored

src/go/build/testdata/directives/c_test.go

@@ -0,0 +1,5 @@
+//go:xtest1
+
+package p_test
+
+//go:ignored

src/go/build/testdata/directives/d_test.go

@@ -0,0 +1,4 @@
+//go:xtest2
+//go:xtest3
+
+package p_test

src/go/build/testdata/directives/eve.go

@@ -0,0 +1,4 @@
+//go:plant
+//axiom:plant
+
+package p