Do not write build info if there are no files to emit

src/compiler/builder.ts

@@ -251,6 +251,7 @@ namespace ts {
             state.seenAffectedFiles = createMap<true>();
         }
 
+        state.emittedBuildInfo = !state.changedFilesSet.size && !state.affectedFilesPendingEmit;
         return state;
     }
 

src/testRunner/unittests/tsc/helpers.ts

@@ -169,9 +169,15 @@ namespace ts {
         Initial = "initial-build",
         IncrementalDtsChange = "incremental-declaration-changes",
         IncrementalDtsUnchanged = "incremental-declaration-doesnt-change",
-        IncrementalHeadersChange = "incremental-headers-change-without-dts-changes"
+        IncrementalHeadersChange = "incremental-headers-change-without-dts-changes",
+        NoChangeRun ="no-change-run"
     }
 
+    export const noChangeRun: TscIncremental = {
+        buildKind: BuildKind.NoChangeRun,
+        modifyFs: noop
+    };
+
     export interface TscCompile {
         scenario: string;
         subScenario: string;

src/testRunner/unittests/tsc/incremental.ts

@@ -17,13 +17,10 @@ namespace ts {
                     }`,
             }),
             commandLineArgs: ["--incremental", "--p", "src/project", "--tsBuildInfoFile", "src/project/.tsbuildinfo"],
-            incrementalScenarios: [{
-                buildKind: BuildKind.IncrementalDtsUnchanged,
-                modifyFs: noop,
-            }]
+            incrementalScenarios: [noChangeRun]
         });
 
-        verifyTsc({
+        verifyTscIncrementalEdits({
             scenario: "incremental",
             subScenario: "when passing rootDir from commandline",
             fs: () => loadProjectFromFiles({
@@ -37,6 +34,25 @@ namespace ts {
                     }`,
             }),
             commandLineArgs: ["--p", "src/project", "--rootDir", "src/project/src"],
+            incrementalScenarios: [noChangeRun]
+        });
+
+        verifyTscIncrementalEdits({
+            scenario: "incremental",
+            subScenario: "with only dts files",
+            fs: () => loadProjectFromFiles({
+                "/src/project/src/main.d.ts": "export const x = 10;",
+                "/src/project/src/another.d.ts": "export const y = 10;",
+                "/src/project/tsconfig.json": "{}",
+            }),
+            commandLineArgs: ["--incremental", "--p", "src/project"],
+            incrementalScenarios: [
+                noChangeRun,
+                {
+                    buildKind: BuildKind.IncrementalDtsUnchanged,
+                    modifyFs: fs => appendText(fs, "/src/project/src/main.d.ts", "export const xy = 100;")
+                }
+            ]
         });
     });
 }

tests/baselines/reference/tsc/incremental/incremental-declaration-doesnt-change/with-only-dts-files.js

@@ -0,0 +1,41 @@
+//// [/lib/incremental-declaration-doesnt-changeOutput.txt]
+/lib/tsc --incremental --p src/project
+exitCode:: 0
+
+
+//// [/src/project/src/main.d.ts]
+export const x = 10;export const xy = 100;
+
+//// [/src/project/tsconfig.tsbuildinfo]
+{
+  "program": {
+    "fileInfos": {
+      "../../lib/lib.d.ts": {
+        "version": "3858781397-/// <reference no-default-lib=\"true\"/>\ninterface Boolean {}\ninterface Function {}\ninterface CallableFunction {}\ninterface NewableFunction {}\ninterface IArguments {}\ninterface Number { toExponential: any; }\ninterface Object {}\ninterface RegExp {}\ninterface String { charAt: any; }\ninterface Array<T> { length: number; [n: number]: T; }\ninterface ReadonlyArray<T> {}\ndeclare const console: { log(msg: any): void; };",
+        "signature": "3858781397-/// <reference no-default-lib=\"true\"/>\ninterface Boolean {}\ninterface Function {}\ninterface CallableFunction {}\ninterface NewableFunction {}\ninterface IArguments {}\ninterface Number { toExponential: any; }\ninterface Object {}\ninterface RegExp {}\ninterface String { charAt: any; }\ninterface Array<T> { length: number; [n: number]: T; }\ninterface ReadonlyArray<T> {}\ndeclare const console: { log(msg: any): void; };"
+      },
+      "./src/another.d.ts": {
+        "version": "-13729955264-export const y = 10;",
+        "signature": "-13729955264-export const y = 10;"
+      },
+      "./src/main.d.ts": {
+        "version": "-10808461502-export const x = 10;export const xy = 100;",
+        "signature": "-10808461502-export const x = 10;export const xy = 100;"
+      }
+    },
+    "options": {
+      "incremental": true,
+      "project": "./",
+      "configFilePath": "./tsconfig.json"
+    },
+    "referencedMap": {},
+    "exportedModulesMap": {},
+    "semanticDiagnosticsPerFile": [
+      "../../lib/lib.d.ts",
+      "./src/another.d.ts",
+      "./src/main.d.ts"
+    ]
+  },
+  "version": "FakeTSVersion"
+}
+

tests/baselines/reference/tsc/incremental/initial-build/with-only-dts-files.js

@@ -0,0 +1,38 @@
+//// [/lib/initial-buildOutput.txt]
+/lib/tsc --incremental --p src/project
+exitCode:: 0
+
+
+//// [/src/project/tsconfig.tsbuildinfo]
+{
+  "program": {
+    "fileInfos": {
+      "../../lib/lib.d.ts": {
+        "version": "3858781397-/// <reference no-default-lib=\"true\"/>\ninterface Boolean {}\ninterface Function {}\ninterface CallableFunction {}\ninterface NewableFunction {}\ninterface IArguments {}\ninterface Number { toExponential: any; }\ninterface Object {}\ninterface RegExp {}\ninterface String { charAt: any; }\ninterface Array<T> { length: number; [n: number]: T; }\ninterface ReadonlyArray<T> {}\ndeclare const console: { log(msg: any): void; };",
+        "signature": "3858781397-/// <reference no-default-lib=\"true\"/>\ninterface Boolean {}\ninterface Function {}\ninterface CallableFunction {}\ninterface NewableFunction {}\ninterface IArguments {}\ninterface Number { toExponential: any; }\ninterface Object {}\ninterface RegExp {}\ninterface String { charAt: any; }\ninterface Array<T> { length: number; [n: number]: T; }\ninterface ReadonlyArray<T> {}\ndeclare const console: { log(msg: any): void; };"
+      },
+      "./src/another.d.ts": {
+        "version": "-13729955264-export const y = 10;",
+        "signature": "-13729955264-export const y = 10;"
+      },
+      "./src/main.d.ts": {
+        "version": "-10726455937-export const x = 10;",
+        "signature": "-10726455937-export const x = 10;"
+      }
+    },
+    "options": {
+      "incremental": true,
+      "project": "./",
+      "configFilePath": "./tsconfig.json"
+    },
+    "referencedMap": {},
+    "exportedModulesMap": {},
+    "semanticDiagnosticsPerFile": [
+      "../../lib/lib.d.ts",
+      "./src/another.d.ts",
+      "./src/main.d.ts"
+    ]
+  },
+  "version": "FakeTSVersion"
+}
+

tests/baselines/reference/tsc/incremental/no-change-run/when-passing-filename-for-buildinfo-on-commandline.js

@@ -0,0 +1,5 @@
+//// [/lib/no-change-runOutput.txt]
+/lib/tsc --incremental --p src/project --tsBuildInfoFile src/project/.tsbuildinfo
+exitCode:: 0
+
+

tests/baselines/reference/tsc/incremental/no-change-run/when-passing-rootDir-from-commandline.js

@@ -0,0 +1,5 @@
+//// [/lib/no-change-runOutput.txt]
+/lib/tsc --p src/project --rootDir src/project/src
+exitCode:: 0
+
+

tests/baselines/reference/tsc/incremental/no-change-run/with-only-dts-files.js

@@ -0,0 +1,5 @@
+//// [/lib/no-change-runOutput.txt]
+/lib/tsc --incremental --p src/project
+exitCode:: 0
+
+