performance_test.go

Documentation: go/printer

     1  // Copyright 2009 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  // This file implements a simple printer performance benchmark:
     6  // go test -bench=BenchmarkPrint
     7  
     8  package printer
     9  
    10  import (
    11  	"bytes"
    12  	"go/ast"
    13  	"go/parser"
    14  	"io"
    15  	"log"
    16  	"os"
    17  	"testing"
    18  )
    19  
    20  var testfile *ast.File
    21  
    22  func testprint(out io.Writer, file *ast.File) {
    23  	if err := (&Config{TabIndent | UseSpaces | normalizeNumbers, 8, 0}).Fprint(out, fset, file); err != nil {
    24  		log.Fatalf("print error: %s", err)
    25  	}
    26  }
    27  
    28  // cannot initialize in init because (printer) Fprint launches goroutines.
    29  func initialize() {
    30  	const filename = "testdata/parser.go"
    31  
    32  	src, err := os.ReadFile(filename)
    33  	if err != nil {
    34  		log.Fatalf("%s", err)
    35  	}
    36  
    37  	file, err := parser.ParseFile(fset, filename, src, parser.ParseComments)
    38  	if err != nil {
    39  		log.Fatalf("%s", err)
    40  	}
    41  
    42  	var buf bytes.Buffer
    43  	testprint(&buf, file)
    44  	if !bytes.Equal(buf.Bytes(), src) {
    45  		log.Fatalf("print error: %s not idempotent", filename)
    46  	}
    47  
    48  	testfile = file
    49  }
    50  
    51  func BenchmarkPrint(b *testing.B) {
    52  	if testfile == nil {
    53  		initialize()
    54  	}
    55  	for i := 0; i < b.N; i++ {
    56  		testprint(io.Discard, testfile)
    57  	}
    58  }
    59
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