Fix incremental builder re-emitting entire import closure on non-shape-changing edits

internal/execute/incremental/affectedfileshandler.go

@@ -10,7 +10,6 @@ import (
 	"github.com/microsoft/typescript-go/internal/ast"
 	"github.com/microsoft/typescript-go/internal/checker"
 	"github.com/microsoft/typescript-go/internal/collections"
-	"github.com/microsoft/typescript-go/internal/compiler"
 	"github.com/microsoft/typescript-go/internal/core"
 	"github.com/microsoft/typescript-go/internal/tspath"
 )
@@ -67,19 +66,7 @@ func (h *affectedFilesHandler) removeDiagnosticsOfLibraryFiles() {
 }
 
 func (h *affectedFilesHandler) computeDtsSignature(file *ast.SourceFile) string {
-	var signature string
-	h.program.program.Emit(h.ctx, compiler.EmitOptions{
-		TargetSourceFiles: core.SingleElementSlice(file),
-		EmitOnly:          compiler.EmitOnlyForcedDts,
-		WriteFile: func(fileName string, text string, data *compiler.WriteFileData) error {
-			if !tspath.IsDeclarationFileName(fileName) {
-				panic("File extension for signature expected to be dts, got : " + fileName)
-			}
-			signature = h.program.snapshot.computeSignatureWithDiagnostics(file, text, data)
-			return nil
-		},
-	})
-	return signature
+	return h.program.snapshot.computeDtsSignatureOfFile(h.ctx, h.program.program, file)
 }
 
 func (h *affectedFilesHandler) updateShapeSignature(file *ast.SourceFile, useFileVersionAsSignature bool) bool {
@@ -101,8 +88,13 @@ func (h *affectedFilesHandler) updateShapeSignature(file *ast.SourceFile, useFil
 	}
 	// Default is to use file version as signature
 	if update.signature == "" {
-		update.signature = info.version
-		update.kind = SignatureUpdateKindUsedVersion
+		if useFileVersionAsSignature && prevSignature != "" && prevSignature != info.version {
+			update.signature = prevSignature
+			update.kind = SignatureUpdateKindComputedDts
+		} else {
+			update.signature = info.version
+			update.kind = SignatureUpdateKindUsedVersion
+		}
 	}
 	return update.signature != prevSignature
 }

internal/execute/incremental/programtosnapshot.go

@@ -142,6 +142,11 @@ func (t *toProgramSnapshot) computeProgramFileChanges() {
 			} else {
 				t.snapshot.addFileToAffectedFilesPendingEmit(file.Path(), GetFileEmitKind(t.snapshot.options))
 				signature = version
+				if !file.IsDeclarationFile && !t.snapshot.options.GetEmitDeclarations() {
+					if dtsSignature := t.snapshot.computeDtsSignatureOfFile(context.Background(), t.program, file); dtsSignature != "" {
+						signature = dtsSignature
+					}
+				}
 			}
 			t.snapshot.fileInfos.Store(file.Path(), &FileInfo{
 				version:            version,

internal/execute/incremental/snapshot.go

@@ -1,6 +1,7 @@
 package incremental
 
 import (
+	"context"
 	"encoding/hex"
 	"fmt"
 	"strings"
@@ -396,6 +397,22 @@ func (s *snapshot) computeSignatureWithDiagnostics(file *ast.SourceFile, text st
 	return s.computeHash(builder.String())
 }
 
+func (s *snapshot) computeDtsSignatureOfFile(ctx context.Context, program *compiler.Program, file *ast.SourceFile) string {
+	var signature string
+	program.Emit(ctx, compiler.EmitOptions{
+		TargetSourceFiles: core.SingleElementSlice(file),
+		EmitOnly:          compiler.EmitOnlyForcedDts,
+		WriteFile: func(fileName string, text string, data *compiler.WriteFileData) error {
+			if !tspath.IsDeclarationFileName(fileName) {
+				panic("File extension for signature expected to be dts, got : " + fileName)
+			}
+			signature = s.computeSignatureWithDiagnostics(file, text, data)
+			return nil
+		},
+	})
+	return signature
+}
+
 func diagnosticToStringBuilder(diagnostic *ast.Diagnostic, file *ast.SourceFile, builder *strings.Builder) {
 	if diagnostic == nil {
 		return

internal/execute/tsctests/tsc_test.go

@@ -2234,6 +2234,59 @@ func TestTscIncremental(t *testing.T) {
 			},
 			commandLineArgs: []string{"--noEmit"},
 		},
+		{
+			subScenario: "whitespace edit through const enum barrel",
+			files: FileMap{
+				"/home/src/workspaces/project/tsconfig.json": stringtestutil.Dedent(`
+					{
+						"compilerOptions": {
+							"incremental": true,
+							"module": "esnext",
+							"moduleResolution": "bundler",
+							"strict": true,
+						},
+						"include": ["src/**/*.ts"],
+					}`),
+				"/home/src/workspaces/project/src/core.ts": stringtestutil.Dedent(`
+					export interface CoreThing { a: number }
+					export const CORE = 1;
+				`),
+				"/home/src/workspaces/project/src/core-barrel.ts": "export * from './core';\n",
+				"/home/src/workspaces/project/src/mid.ts": stringtestutil.Dedent(`
+					import { CORE, CoreThing } from './core-barrel';
+					export const MID: number = CORE + 1;
+					export function useCore(x: CoreThing): number { return x.a + MID; }
+					export const enum MidMode { A = 1, B = 2 }
+				`),
+				"/home/src/workspaces/project/src/index.ts": "export * from './mid';\n",
+				"/home/src/workspaces/project/src/leaf0.ts": stringtestutil.Dedent(`
+					import { MID } from './index';
+					export const L0: number = MID + 0;
+				`),
+				"/home/src/workspaces/project/src/leaf1.ts": stringtestutil.Dedent(`
+					import { MID } from './index';
+					export const L1: number = MID + 1;
+				`),
+				"/home/src/workspaces/project/src/leaf2.ts": stringtestutil.Dedent(`
+					import { MID } from './index';
+					export const L2: number = MID + 2;
+				`),
+			},
+			edits: []*tscEdit{
+				{
+					caption: "whitespace only edit of mid.ts",
+					edit: func(sys *TestSys) {
+						sys.appendFile("/home/src/workspaces/project/src/mid.ts", "\n")
+					},
+				},
+				{
+					caption: "same whitespace only edit of mid.ts again",
+					edit: func(sys *TestSys) {
+						sys.appendFile("/home/src/workspaces/project/src/mid.ts", "\n")
+					},
+				},
+			},
+		},
 	}
 
 	for _, test := range testCases {