Scribbles, nothing works yet

src/compiler/emitter.ts

@@ -438,6 +438,8 @@ namespace ts {
             if (bundleBuildInfo) bundleBuildInfo.js = printer.bundleFileInfo;
         }
 
+        const horrible: Record<string, readonly SourceFile[]> = {}
+
         function emitDeclarationFileOrBundle(
             sourceFileOrBundle: SourceFile | Bundle | undefined,
             declarationFilePath: string | undefined,
@@ -449,6 +451,13 @@ namespace ts {
                 return;
             }
             const sourceFiles = isSourceFile(sourceFileOrBundle) ? [sourceFileOrBundle] : sourceFileOrBundle.sourceFiles;
+            const key = sourceFiles.map(f => f.fileName).join("|")
+            console.log(key)
+            horrible[key] = sourceFiles
+            // Let's do this WRONG
+            // 1. cache with key=filesForEmit, value=[emit, diagnostics]
+            // 2. include custom transformers in the key, plus "other api things" (??)
+            // Afterward, need to measure performance to see which projects this helps/how much. Ask Andrew about this.
             const filesForEmit = forceDtsEmit ? sourceFiles : filter(sourceFiles, isSourceFileNotJson);
             // Setup and perform the transformation to retrieve declarations from the input files
             const inputListOrBundle = outFile(compilerOptions) ? [factory.createBundle(filesForEmit, !isSourceFile(sourceFileOrBundle) ? sourceFileOrBundle.prepends : undefined)] : filesForEmit;

src/testRunner/unittests/tsbuild/declarationEmit.ts

@@ -114,5 +114,12 @@ export function fn4() {
             }),
             commandLineArgs: ["--b", "/src/packages/pkg2/tsconfig.json", "--verbose"]
         });
+        verifyTsc({
+            scenario: "doubleEmit",
+            subScenario: "cache declaration emit from build",
+            fs: () => loadProjectFromFiles({
+            }),
+            commandLineArgs: ["--b", "/src/packages/pkg2/tsconfig.json", "--verbose"]
+        });
     });
 }

src/testRunner/unittests/tsbuild/emitDeclarationOnly.ts

@@ -8,6 +8,8 @@ namespace ts {
             projFs = undefined!;
         });
 
+        // This is pretty close but the example only has one project. Still it's worth debugging it to see.
+        // (for initial debugging, it's STILl probably easier to attach to ~/dmp/buildbasic/test though)
         function verifyEmitDeclarationOnly(disableMap?: true) {
             verifyTscSerializedIncrementalEdits({
                 subScenario: `only dts output in circular import project with emitDeclarationOnly${disableMap ? "" : " and declarationMap"}`,

src/testRunner/unittests/tsbuild/outFile.ts

@@ -201,6 +201,9 @@ namespace ts {
             modifyFs: fs => replaceText(fs, sources[Project.third][Source.config], `"composite": true,`, ""),
         });
 
+        it("only generates declaration emit once on subsequent edits and recompiles", () => {
+        })
+
         it("rebuilds completely when version in tsbuildinfo doesnt match ts version", () => {
             const { fs, tick } = getFsWithTime(outFileFs);
             const host = fakes.SolutionBuilderHost.create(fs);