example.go

Documentation: go/doc

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Extract example functions from file ASTs.
     6  
     7  package doc
     8  
     9  import (
    10  	"go/ast"
    11  	"go/token"
    12  	"internal/lazyregexp"
    13  	"path"
    14  	"sort"
    15  	"strconv"
    16  	"strings"
    17  	"unicode"
    18  	"unicode/utf8"
    19  )
    20  
    21  // An Example represents an example function found in a test source file.
    22  type Example struct {
    23  	Name        string // name of the item being exemplified (including optional suffix)
    24  	Suffix      string // example suffix, without leading '_' (only populated by NewFromFiles)
    25  	Doc         string // example function doc string
    26  	Code        ast.Node
    27  	Play        *ast.File // a whole program version of the example
    28  	Comments    []*ast.CommentGroup
    29  	Output      string // expected output
    30  	Unordered   bool
    31  	EmptyOutput bool // expect empty output
    32  	Order       int  // original source code order
    33  }
    34  
    35  // Examples returns the examples found in testFiles, sorted by Name field.
    36  // The Order fields record the order in which the examples were encountered.
    37  // The Suffix field is not populated when Examples is called directly, it is
    38  // only populated by [NewFromFiles] for examples it finds in _test.go files.
    39  //
    40  // Playable Examples must be in a package whose name ends in "_test".
    41  // An Example is "playable" (the Play field is non-nil) in either of these
    42  // circumstances:
    43  //   - The example function is self-contained: the function references only
    44  //     identifiers from other packages (or predeclared identifiers, such as
    45  //     "int") and the test file does not include a dot import.
    46  //   - The entire test file is the example: the file contains exactly one
    47  //     example function, zero test, fuzz test, or benchmark function, and at
    48  //     least one top-level function, type, variable, or constant declaration
    49  //     other than the example function.
    50  func Examples(testFiles ...*ast.File) []*Example {
    51  	var list []*Example
    52  	for _, file := range testFiles {
    53  		hasTests := false // file contains tests, fuzz test, or benchmarks
    54  		numDecl := 0      // number of non-import declarations in the file
    55  		var flist []*Example
    56  		for _, decl := range file.Decls {
    57  			if g, ok := decl.(*ast.GenDecl); ok && g.Tok != token.IMPORT {
    58  				numDecl++
    59  				continue
    60  			}
    61  			f, ok := decl.(*ast.FuncDecl)
    62  			if !ok || f.Recv != nil {
    63  				continue
    64  			}
    65  			numDecl++
    66  			name := f.Name.Name
    67  			if isTest(name, "Test") || isTest(name, "Benchmark") || isTest(name, "Fuzz") {
    68  				hasTests = true
    69  				continue
    70  			}
    71  			if !isTest(name, "Example") {
    72  				continue
    73  			}
    74  			if params := f.Type.Params; len(params.List) != 0 {
    75  				continue // function has params; not a valid example
    76  			}
    77  			if f.Body == nil { // ast.File.Body nil dereference (see issue 28044)
    78  				continue
    79  			}
    80  			var doc string
    81  			if f.Doc != nil {
    82  				doc = f.Doc.Text()
    83  			}
    84  			output, unordered, hasOutput := exampleOutput(f.Body, file.Comments)
    85  			flist = append(flist, &Example{
    86  				Name:        name[len("Example"):],
    87  				Doc:         doc,
    88  				Code:        f.Body,
    89  				Play:        playExample(file, f),
    90  				Comments:    file.Comments,
    91  				Output:      output,
    92  				Unordered:   unordered,
    93  				EmptyOutput: output == "" && hasOutput,
    94  				Order:       len(flist),
    95  			})
    96  		}
    97  		if !hasTests && numDecl > 1 && len(flist) == 1 {
    98  			// If this file only has one example function, some
    99  			// other top-level declarations, and no tests or
   100  			// benchmarks, use the whole file as the example.
   101  			flist[0].Code = file
   102  			flist[0].Play = playExampleFile(file)
   103  		}
   104  		list = append(list, flist...)
   105  	}
   106  	// sort by name
   107  	sort.Slice(list, func(i, j int) bool {
   108  		return list[i].Name < list[j].Name
   109  	})
   110  	return list
   111  }
   112  
   113  var outputPrefix = lazyregexp.New(`(?i)^[[:space:]]*(unordered )?output:`)
   114  
   115  // Extracts the expected output and whether there was a valid output comment.
   116  func exampleOutput(b *ast.BlockStmt, comments []*ast.CommentGroup) (output string, unordered, ok bool) {
   117  	if _, last := lastComment(b, comments); last != nil {
   118  		// test that it begins with the correct prefix
   119  		text := last.Text()
   120  		if loc := outputPrefix.FindStringSubmatchIndex(text); loc != nil {
   121  			if loc[2] != -1 {
   122  				unordered = true
   123  			}
   124  			text = text[loc[1]:]
   125  			// Strip zero or more spaces followed by \n or a single space.
   126  			text = strings.TrimLeft(text, " ")
   127  			if len(text) > 0 && text[0] == '\n' {
   128  				text = text[1:]
   129  			}
   130  			return text, unordered, true
   131  		}
   132  	}
   133  	return "", false, false // no suitable comment found
   134  }
   135  
   136  // isTest tells whether name looks like a test, example, fuzz test, or
   137  // benchmark. It is a Test (say) if there is a character after Test that is not
   138  // a lower-case letter. (We don't want Testiness.)
   139  func isTest(name, prefix string) bool {
   140  	if !strings.HasPrefix(name, prefix) {
   141  		return false
   142  	}
   143  	if len(name) == len(prefix) { // "Test" is ok
   144  		return true
   145  	}
   146  	rune, _ := utf8.DecodeRuneInString(name[len(prefix):])
   147  	return !unicode.IsLower(rune)
   148  }
   149  
   150  // playExample synthesizes a new *ast.File based on the provided
   151  // file with the provided function body as the body of main.
   152  func playExample(file *ast.File, f *ast.FuncDecl) *ast.File {
   153  	body := f.Body
   154  
   155  	if !strings.HasSuffix(file.Name.Name, "_test") {
   156  		// We don't support examples that are part of the
   157  		// greater package (yet).
   158  		return nil
   159  	}
   160  
   161  	// Collect top-level declarations in the file.
   162  	topDecls := make(map[*ast.Object]ast.Decl)
   163  	typMethods := make(map[string][]ast.Decl)
   164  
   165  	for _, decl := range file.Decls {
   166  		switch d := decl.(type) {
   167  		case *ast.FuncDecl:
   168  			if d.Recv == nil {
   169  				topDecls[d.Name.Obj] = d
   170  			} else {
   171  				if len(d.Recv.List) == 1 {
   172  					t := d.Recv.List[0].Type
   173  					tname, _ := baseTypeName(t)
   174  					typMethods[tname] = append(typMethods[tname], d)
   175  				}
   176  			}
   177  		case *ast.GenDecl:
   178  			for _, spec := range d.Specs {
   179  				switch s := spec.(type) {
   180  				case *ast.TypeSpec:
   181  					topDecls[s.Name.Obj] = d
   182  				case *ast.ValueSpec:
   183  					for _, name := range s.Names {
   184  						topDecls[name.Obj] = d
   185  					}
   186  				}
   187  			}
   188  		}
   189  	}
   190  
   191  	// Find unresolved identifiers and uses of top-level declarations.
   192  	depDecls, unresolved := findDeclsAndUnresolved(body, topDecls, typMethods)
   193  
   194  	// Remove predeclared identifiers from unresolved list.
   195  	for n := range unresolved {
   196  		if predeclaredTypes[n] || predeclaredConstants[n] || predeclaredFuncs[n] {
   197  			delete(unresolved, n)
   198  		}
   199  	}
   200  
   201  	// Use unresolved identifiers to determine the imports used by this
   202  	// example. The heuristic assumes package names match base import
   203  	// paths for imports w/o renames (should be good enough most of the time).
   204  	var namedImports []ast.Spec
   205  	var blankImports []ast.Spec // _ imports
   206  
   207  	// To preserve the blank lines between groups of imports, find the
   208  	// start position of each group, and assign that position to all
   209  	// imports from that group.
   210  	groupStarts := findImportGroupStarts(file.Imports)
   211  	groupStart := func(s *ast.ImportSpec) token.Pos {
   212  		for i, start := range groupStarts {
   213  			if s.Path.ValuePos < start {
   214  				return groupStarts[i-1]
   215  			}
   216  		}
   217  		return groupStarts[len(groupStarts)-1]
   218  	}
   219  
   220  	for _, s := range file.Imports {
   221  		p, err := strconv.Unquote(s.Path.Value)
   222  		if err != nil {
   223  			continue
   224  		}
   225  		if p == "syscall/js" {
   226  			// We don't support examples that import syscall/js,
   227  			// because the package syscall/js is not available in the playground.
   228  			return nil
   229  		}
   230  		n := path.Base(p)
   231  		if s.Name != nil {
   232  			n = s.Name.Name
   233  			switch n {
   234  			case "_":
   235  				blankImports = append(blankImports, s)
   236  				continue
   237  			case ".":
   238  				// We can't resolve dot imports (yet).
   239  				return nil
   240  			}
   241  		}
   242  		if unresolved[n] {
   243  			// Copy the spec and its path to avoid modifying the original.
   244  			spec := *s
   245  			path := *s.Path
   246  			spec.Path = &path
   247  			spec.Path.ValuePos = groupStart(&spec)
   248  			namedImports = append(namedImports, &spec)
   249  			delete(unresolved, n)
   250  		}
   251  	}
   252  
   253  	// If there are other unresolved identifiers, give up because this
   254  	// synthesized file is not going to build.
   255  	if len(unresolved) > 0 {
   256  		return nil
   257  	}
   258  
   259  	// Include documentation belonging to blank imports.
   260  	var comments []*ast.CommentGroup
   261  	for _, s := range blankImports {
   262  		if c := s.(*ast.ImportSpec).Doc; c != nil {
   263  			comments = append(comments, c)
   264  		}
   265  	}
   266  
   267  	// Include comments that are inside the function body.
   268  	for _, c := range file.Comments {
   269  		if body.Pos() <= c.Pos() && c.End() <= body.End() {
   270  			comments = append(comments, c)
   271  		}
   272  	}
   273  
   274  	// Strip the "Output:" or "Unordered output:" comment and adjust body
   275  	// end position.
   276  	body, comments = stripOutputComment(body, comments)
   277  
   278  	// Include documentation belonging to dependent declarations.
   279  	for _, d := range depDecls {
   280  		switch d := d.(type) {
   281  		case *ast.GenDecl:
   282  			if d.Doc != nil {
   283  				comments = append(comments, d.Doc)
   284  			}
   285  		case *ast.FuncDecl:
   286  			if d.Doc != nil {
   287  				comments = append(comments, d.Doc)
   288  			}
   289  		}
   290  	}
   291  
   292  	// Synthesize import declaration.
   293  	importDecl := &ast.GenDecl{
   294  		Tok:    token.IMPORT,
   295  		Lparen: 1, // Need non-zero Lparen and Rparen so that printer
   296  		Rparen: 1, // treats this as a factored import.
   297  	}
   298  	importDecl.Specs = append(namedImports, blankImports...)
   299  
   300  	// Synthesize main function.
   301  	funcDecl := &ast.FuncDecl{
   302  		Name: ast.NewIdent("main"),
   303  		Type: f.Type,
   304  		Body: body,
   305  	}
   306  
   307  	decls := make([]ast.Decl, 0, 2+len(depDecls))
   308  	decls = append(decls, importDecl)
   309  	decls = append(decls, depDecls...)
   310  	decls = append(decls, funcDecl)
   311  
   312  	sort.Slice(decls, func(i, j int) bool {
   313  		return decls[i].Pos() < decls[j].Pos()
   314  	})
   315  	sort.Slice(comments, func(i, j int) bool {
   316  		return comments[i].Pos() < comments[j].Pos()
   317  	})
   318  
   319  	// Synthesize file.
   320  	return &ast.File{
   321  		Name:     ast.NewIdent("main"),
   322  		Decls:    decls,
   323  		Comments: comments,
   324  	}
   325  }
   326  
   327  // findDeclsAndUnresolved returns all the top-level declarations mentioned in
   328  // the body, and a set of unresolved symbols (those that appear in the body but
   329  // have no declaration in the program).
   330  //
   331  // topDecls maps objects to the top-level declaration declaring them (not
   332  // necessarily obj.Decl, as obj.Decl will be a Spec for GenDecls, but
   333  // topDecls[obj] will be the GenDecl itself).
   334  func findDeclsAndUnresolved(body ast.Node, topDecls map[*ast.Object]ast.Decl, typMethods map[string][]ast.Decl) ([]ast.Decl, map[string]bool) {
   335  	// This function recursively finds every top-level declaration used
   336  	// transitively by the body, populating usedDecls and usedObjs. Then it
   337  	// trims down the declarations to include only the symbols actually
   338  	// referenced by the body.
   339  
   340  	unresolved := make(map[string]bool)
   341  	var depDecls []ast.Decl
   342  	usedDecls := make(map[ast.Decl]bool)   // set of top-level decls reachable from the body
   343  	usedObjs := make(map[*ast.Object]bool) // set of objects reachable from the body (each declared by a usedDecl)
   344  
   345  	var inspectFunc func(ast.Node) bool
   346  	inspectFunc = func(n ast.Node) bool {
   347  		switch e := n.(type) {
   348  		case *ast.Ident:
   349  			if e.Obj == nil && e.Name != "_" {
   350  				unresolved[e.Name] = true
   351  			} else if d := topDecls[e.Obj]; d != nil {
   352  
   353  				usedObjs[e.Obj] = true
   354  				if !usedDecls[d] {
   355  					usedDecls[d] = true
   356  					depDecls = append(depDecls, d)
   357  				}
   358  			}
   359  			return true
   360  		case *ast.SelectorExpr:
   361  			// For selector expressions, only inspect the left hand side.
   362  			// (For an expression like fmt.Println, only add "fmt" to the
   363  			// set of unresolved names, not "Println".)
   364  			ast.Inspect(e.X, inspectFunc)
   365  			return false
   366  		case *ast.KeyValueExpr:
   367  			// For key value expressions, only inspect the value
   368  			// as the key should be resolved by the type of the
   369  			// composite literal.
   370  			ast.Inspect(e.Value, inspectFunc)
   371  			return false
   372  		}
   373  		return true
   374  	}
   375  
   376  	inspectFieldList := func(fl *ast.FieldList) {
   377  		if fl != nil {
   378  			for _, f := range fl.List {
   379  				ast.Inspect(f.Type, inspectFunc)
   380  			}
   381  		}
   382  	}
   383  
   384  	// Find the decls immediately referenced by body.
   385  	ast.Inspect(body, inspectFunc)
   386  	// Now loop over them, adding to the list when we find a new decl that the
   387  	// body depends on. Keep going until we don't find anything new.
   388  	for i := 0; i < len(depDecls); i++ {
   389  		switch d := depDecls[i].(type) {
   390  		case *ast.FuncDecl:
   391  			// Inpect type parameters.
   392  			inspectFieldList(d.Type.TypeParams)
   393  			// Inspect types of parameters and results. See #28492.
   394  			inspectFieldList(d.Type.Params)
   395  			inspectFieldList(d.Type.Results)
   396  
   397  			// Functions might not have a body. See #42706.
   398  			if d.Body != nil {
   399  				ast.Inspect(d.Body, inspectFunc)
   400  			}
   401  		case *ast.GenDecl:
   402  			for _, spec := range d.Specs {
   403  				switch s := spec.(type) {
   404  				case *ast.TypeSpec:
   405  					inspectFieldList(s.TypeParams)
   406  					ast.Inspect(s.Type, inspectFunc)
   407  					depDecls = append(depDecls, typMethods[s.Name.Name]...)
   408  				case *ast.ValueSpec:
   409  					if s.Type != nil {
   410  						ast.Inspect(s.Type, inspectFunc)
   411  					}
   412  					for _, val := range s.Values {
   413  						ast.Inspect(val, inspectFunc)
   414  					}
   415  				}
   416  			}
   417  		}
   418  	}
   419  
   420  	// Some decls include multiple specs, such as a variable declaration with
   421  	// multiple variables on the same line, or a parenthesized declaration. Trim
   422  	// the declarations to include only the specs that are actually mentioned.
   423  	// However, if there is a constant group with iota, leave it all: later
   424  	// constant declarations in the group may have no value and so cannot stand
   425  	// on their own, and removing any constant from the group could change the
   426  	// values of subsequent ones.
   427  	// See testdata/examples/iota.go for a minimal example.
   428  	var ds []ast.Decl
   429  	for _, d := range depDecls {
   430  		switch d := d.(type) {
   431  		case *ast.FuncDecl:
   432  			ds = append(ds, d)
   433  		case *ast.GenDecl:
   434  			containsIota := false // does any spec have iota?
   435  			// Collect all Specs that were mentioned in the example.
   436  			var specs []ast.Spec
   437  			for _, s := range d.Specs {
   438  				switch s := s.(type) {
   439  				case *ast.TypeSpec:
   440  					if usedObjs[s.Name.Obj] {
   441  						specs = append(specs, s)
   442  					}
   443  				case *ast.ValueSpec:
   444  					if !containsIota {
   445  						containsIota = hasIota(s)
   446  					}
   447  					// A ValueSpec may have multiple names (e.g. "var a, b int").
   448  					// Keep only the names that were mentioned in the example.
   449  					// Exception: the multiple names have a single initializer (which
   450  					// would be a function call with multiple return values). In that
   451  					// case, keep everything.
   452  					if len(s.Names) > 1 && len(s.Values) == 1 {
   453  						specs = append(specs, s)
   454  						continue
   455  					}
   456  					ns := *s
   457  					ns.Names = nil
   458  					ns.Values = nil
   459  					for i, n := range s.Names {
   460  						if usedObjs[n.Obj] {
   461  							ns.Names = append(ns.Names, n)
   462  							if s.Values != nil {
   463  								ns.Values = append(ns.Values, s.Values[i])
   464  							}
   465  						}
   466  					}
   467  					if len(ns.Names) > 0 {
   468  						specs = append(specs, &ns)
   469  					}
   470  				}
   471  			}
   472  			if len(specs) > 0 {
   473  				// Constant with iota? Keep it all.
   474  				if d.Tok == token.CONST && containsIota {
   475  					ds = append(ds, d)
   476  				} else {
   477  					// Synthesize a GenDecl with just the Specs we need.
   478  					nd := *d // copy the GenDecl
   479  					nd.Specs = specs
   480  					if len(specs) == 1 {
   481  						// Remove grouping parens if there is only one spec.
   482  						nd.Lparen = 0
   483  					}
   484  					ds = append(ds, &nd)
   485  				}
   486  			}
   487  		}
   488  	}
   489  	return ds, unresolved
   490  }
   491  
   492  func hasIota(s ast.Spec) bool {
   493  	has := false
   494  	ast.Inspect(s, func(n ast.Node) bool {
   495  		// Check that this is the special built-in "iota" identifier, not
   496  		// a user-defined shadow.
   497  		if id, ok := n.(*ast.Ident); ok && id.Name == "iota" && id.Obj == nil {
   498  			has = true
   499  			return false
   500  		}
   501  		return true
   502  	})
   503  	return has
   504  }
   505  
   506  // findImportGroupStarts finds the start positions of each sequence of import
   507  // specs that are not separated by a blank line.
   508  func findImportGroupStarts(imps []*ast.ImportSpec) []token.Pos {
   509  	startImps := findImportGroupStarts1(imps)
   510  	groupStarts := make([]token.Pos, len(startImps))
   511  	for i, imp := range startImps {
   512  		groupStarts[i] = imp.Pos()
   513  	}
   514  	return groupStarts
   515  }
   516  
   517  // Helper for findImportGroupStarts to ease testing.
   518  func findImportGroupStarts1(origImps []*ast.ImportSpec) []*ast.ImportSpec {
   519  	// Copy to avoid mutation.
   520  	imps := make([]*ast.ImportSpec, len(origImps))
   521  	copy(imps, origImps)
   522  	// Assume the imports are sorted by position.
   523  	sort.Slice(imps, func(i, j int) bool { return imps[i].Pos() < imps[j].Pos() })
   524  	// Assume gofmt has been applied, so there is a blank line between adjacent imps
   525  	// if and only if they are more than 2 positions apart (newline, tab).
   526  	var groupStarts []*ast.ImportSpec
   527  	prevEnd := token.Pos(-2)
   528  	for _, imp := range imps {
   529  		if imp.Pos()-prevEnd > 2 {
   530  			groupStarts = append(groupStarts, imp)
   531  		}
   532  		prevEnd = imp.End()
   533  		// Account for end-of-line comments.
   534  		if imp.Comment != nil {
   535  			prevEnd = imp.Comment.End()
   536  		}
   537  	}
   538  	return groupStarts
   539  }
   540  
   541  // playExampleFile takes a whole file example and synthesizes a new *ast.File
   542  // such that the example is function main in package main.
   543  func playExampleFile(file *ast.File) *ast.File {
   544  	// Strip copyright comment if present.
   545  	comments := file.Comments
   546  	if len(comments) > 0 && strings.HasPrefix(comments[0].Text(), "Copyright") {
   547  		comments = comments[1:]
   548  	}
   549  
   550  	// Copy declaration slice, rewriting the ExampleX function to main.
   551  	var decls []ast.Decl
   552  	for _, d := range file.Decls {
   553  		if f, ok := d.(*ast.FuncDecl); ok && isTest(f.Name.Name, "Example") {
   554  			// Copy the FuncDecl, as it may be used elsewhere.
   555  			newF := *f
   556  			newF.Name = ast.NewIdent("main")
   557  			newF.Body, comments = stripOutputComment(f.Body, comments)
   558  			d = &newF
   559  		}
   560  		decls = append(decls, d)
   561  	}
   562  
   563  	// Copy the File, as it may be used elsewhere.
   564  	f := *file
   565  	f.Name = ast.NewIdent("main")
   566  	f.Decls = decls
   567  	f.Comments = comments
   568  	return &f
   569  }
   570  
   571  // stripOutputComment finds and removes the "Output:" or "Unordered output:"
   572  // comment from body and comments, and adjusts the body block's end position.
   573  func stripOutputComment(body *ast.BlockStmt, comments []*ast.CommentGroup) (*ast.BlockStmt, []*ast.CommentGroup) {
   574  	// Do nothing if there is no "Output:" or "Unordered output:" comment.
   575  	i, last := lastComment(body, comments)
   576  	if last == nil || !outputPrefix.MatchString(last.Text()) {
   577  		return body, comments
   578  	}
   579  
   580  	// Copy body and comments, as the originals may be used elsewhere.
   581  	newBody := &ast.BlockStmt{
   582  		Lbrace: body.Lbrace,
   583  		List:   body.List,
   584  		Rbrace: last.Pos(),
   585  	}
   586  	newComments := make([]*ast.CommentGroup, len(comments)-1)
   587  	copy(newComments, comments[:i])
   588  	copy(newComments[i:], comments[i+1:])
   589  	return newBody, newComments
   590  }
   591  
   592  // lastComment returns the last comment inside the provided block.
   593  func lastComment(b *ast.BlockStmt, c []*ast.CommentGroup) (i int, last *ast.CommentGroup) {
   594  	if b == nil {
   595  		return
   596  	}
   597  	pos, end := b.Pos(), b.End()
   598  	for j, cg := range c {
   599  		if cg.Pos() < pos {
   600  			continue
   601  		}
   602  		if cg.End() > end {
   603  			break
   604  		}
   605  		i, last = j, cg
   606  	}
   607  	return
   608  }
   609  
   610  // classifyExamples classifies examples and assigns them to the Examples field
   611  // of the relevant Func, Type, or Package that the example is associated with.
   612  //
   613  // The classification process is ambiguous in some cases:
   614  //
   615  //   - ExampleFoo_Bar matches a type named Foo_Bar
   616  //     or a method named Foo.Bar.
   617  //   - ExampleFoo_bar matches a type named Foo_bar
   618  //     or Foo (with a "bar" suffix).
   619  //
   620  // Examples with malformed names are not associated with anything.
   621  func classifyExamples(p *Package, examples []*Example) {
   622  	if len(examples) == 0 {
   623  		return
   624  	}
   625  	// Mapping of names for funcs, types, and methods to the example listing.
   626  	ids := make(map[string]*[]*Example)
   627  	ids[""] = &p.Examples // package-level examples have an empty name
   628  	for _, f := range p.Funcs {
   629  		if !token.IsExported(f.Name) {
   630  			continue
   631  		}
   632  		ids[f.Name] = &f.Examples
   633  	}
   634  	for _, t := range p.Types {
   635  		if !token.IsExported(t.Name) {
   636  			continue
   637  		}
   638  		ids[t.Name] = &t.Examples
   639  		for _, f := range t.Funcs {
   640  			if !token.IsExported(f.Name) {
   641  				continue
   642  			}
   643  			ids[f.Name] = &f.Examples
   644  		}
   645  		for _, m := range t.Methods {
   646  			if !token.IsExported(m.Name) {
   647  				continue
   648  			}
   649  			ids[strings.TrimPrefix(nameWithoutInst(m.Recv), "*")+"_"+m.Name] = &m.Examples
   650  		}
   651  	}
   652  
   653  	// Group each example with the associated func, type, or method.
   654  	for _, ex := range examples {
   655  		// Consider all possible split points for the suffix
   656  		// by starting at the end of string (no suffix case),
   657  		// then trying all positions that contain a '_' character.
   658  		//
   659  		// An association is made on the first successful match.
   660  		// Examples with malformed names that match nothing are skipped.
   661  		for i := len(ex.Name); i >= 0; i = strings.LastIndexByte(ex.Name[:i], '_') {
   662  			prefix, suffix, ok := splitExampleName(ex.Name, i)
   663  			if !ok {
   664  				continue
   665  			}
   666  			exs, ok := ids[prefix]
   667  			if !ok {
   668  				continue
   669  			}
   670  			ex.Suffix = suffix
   671  			*exs = append(*exs, ex)
   672  			break
   673  		}
   674  	}
   675  
   676  	// Sort list of example according to the user-specified suffix name.
   677  	for _, exs := range ids {
   678  		sort.Slice((*exs), func(i, j int) bool {
   679  			return (*exs)[i].Suffix < (*exs)[j].Suffix
   680  		})
   681  	}
   682  }
   683  
   684  // nameWithoutInst returns name if name has no brackets. If name contains
   685  // brackets, then it returns name with all the contents between (and including)
   686  // the outermost left and right bracket removed.
   687  //
   688  // Adapted from debug/gosym/symtab.go:Sym.nameWithoutInst.
   689  func nameWithoutInst(name string) string {
   690  	start := strings.Index(name, "[")
   691  	if start < 0 {
   692  		return name
   693  	}
   694  	end := strings.LastIndex(name, "]")
   695  	if end < 0 {
   696  		// Malformed name, should contain closing bracket too.
   697  		return name
   698  	}
   699  	return name[0:start] + name[end+1:]
   700  }
   701  
   702  // splitExampleName attempts to split example name s at index i,
   703  // and reports if that produces a valid split. The suffix may be
   704  // absent. Otherwise, it must start with a lower-case letter and
   705  // be preceded by '_'.
   706  //
   707  // One of i == len(s) or s[i] == '_' must be true.
   708  func splitExampleName(s string, i int) (prefix, suffix string, ok bool) {
   709  	if i == len(s) {
   710  		return s, "", true
   711  	}
   712  	if i == len(s)-1 {
   713  		return "", "", false
   714  	}
   715  	prefix, suffix = s[:i], s[i+1:]
   716  	return prefix, suffix, isExampleSuffix(suffix)
   717  }
   718  
   719  func isExampleSuffix(s string) bool {
   720  	r, size := utf8.DecodeRuneInString(s)
   721  	return size > 0 && unicode.IsLower(r)
   722  }
   723
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