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Reduce string copies and allocations when emitting inlined sourcemaps #1550

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Reduce string copies and allocations when emitting inlined sourcemaps #1550

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6 changes: 1 addition & 5 deletions internal/compiler/emitter.go
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Original file line number Diff line number Diff line change
@@ -1,8 +1,6 @@
package compiler

import (
"encoding/base64"

"github.com/microsoft/typescript-go/internal/ast"
"github.com/microsoft/typescript-go/internal/binder"
"github.com/microsoft/typescript-go/internal/core"
Expand Down Expand Up @@ -335,9 +333,7 @@ func (e *emitter) getSourceMapDirectory(mapOptions *core.CompilerOptions, filePa
func (e *emitter) getSourceMappingURL(mapOptions *core.CompilerOptions, sourceMapGenerator *sourcemap.Generator, filePath string, sourceMapFilePath string, sourceFile *ast.SourceFile) string {
if mapOptions.InlineSourceMap.IsTrue() {
// Encode the sourceMap into the sourceMap url
sourceMapText := sourceMapGenerator.String()
base64SourceMapText := base64.StdEncoding.EncodeToString([]byte(sourceMapText))
return "data:application/json;base64," + base64SourceMapText
return sourceMapGenerator.Base64DataURL()
}

sourceMapFile := tspath.GetBaseFileName(tspath.NormalizeSlashes(sourceMapFilePath))
Expand Down
23 changes: 19 additions & 4 deletions internal/sourcemap/generator.go
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Original file line number Diff line number Diff line change
@@ -1,11 +1,13 @@
package sourcemap

import (
"encoding/base64"
"encoding/json"

Check failure on line 5 in internal/sourcemap/generator.go

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import 'encoding/json' is not allowed from list 'main': Use "github.com/go-json-experiment/json" instead. (depguard)
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Not really sure why you swapped out the json import?

"errors"
"slices"
"strings"
"unsafe"

"github.com/go-json-experiment/json"
"github.com/microsoft/typescript-go/internal/tspath"
)

Expand Down Expand Up @@ -333,13 +335,26 @@
}
}

// Gets the string representation of the source map
func (gen *Generator) String() string {
func (gen *Generator) bytes() []byte {
buf, err := json.Marshal(gen.RawSourceMap())
if err != nil {
panic(err.Error())
}
return string(buf)
return buf
}

// Gets the string representation of the source map
func (gen *Generator) String() string {
return string(gen.bytes())
}

func (gen *Generator) Base64DataURL() string {
const prefix = "data:application/json;base64,"
data := gen.bytes()
buf := make([]byte, len(prefix)+base64.StdEncoding.EncodedLen(len(data)))
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this can also be done via strings.Builder with Grow and Write if preferred, it's essentially the same unsafe.String trick under the hood

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Yes, avoiding unsafe is preferred.

copy(buf, prefix)
base64.StdEncoding.Encode(buf[len(prefix):], data)
return unsafe.String(unsafe.SliceData(buf), len(buf))
}

func base64FormatEncode(value int) rune {
Expand Down
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