command-line --incremental flag doesn't speed up compilation

[mmkal]

When using tsc without tsconfig.json, i.e. passing compiler options via command line, subsequent incremental builds don't seem to speed up at all.

Unless I'm missing something about what exactly --incremental is supposed to do, this seems wrong. The command I'm running looks something like tsc --incremental --tsBuildInfoFile abc.json --outDir xyz path/to/input.ts. See below for exact repro.

TypeScript Version: 3.7.0-dev.20190928 (also 3.6.2, and likely earlier versions too)

Search Terms:

tsc, incremental, tsBuildInfoFile

Code

Here's a full repro you can run with bash, which installs dependencies, writes example code and runs tsc a few times (I'm using node 10.16.0, npm 6.9.0, MacOS):

mkdir tsc-incremental-bug-repro
cd $_
npm init -y
npm i [email protected] # what I got today from npm i typescript@next
mkdir -p packages/logger/src
cd packages/logger
npm init -y
npm i [email protected] @types/[email protected]
echo "import * as winston from 'winston'" >> src/index.ts
echo "export const mylogger = winston" >> src/index.ts
cd ../..
time npx tsc --incremental --tsBuildInfoFile packages/logger/buildinfo.json --outDir packages/logger/dist packages/logger/src/index.ts
time npx tsc --incremental --tsBuildInfoFile packages/logger/buildinfo.json --outDir packages/logger/dist packages/logger/src/index.ts
time npx tsc --incremental --tsBuildInfoFile packages/logger/buildinfo.json --outDir packages/logger/dist packages/logger/src/index.ts
time npx tsc --incremental --tsBuildInfoFile packages/logger/buildinfo.json --outDir packages/logger/dist packages/logger/src/index.ts

Each call to time npx tsc ... gave a similar overall time, about 5s on my machine. This seems very slow given it's compiling one tiny file. It'd be not-too-bad if it was only on the first build. As far as I can tell nothing is changing in the tsBuildInfoFile.

Note - this example is using a pseudo-monorepo structure since that's the way I found it IRL, but here there's only one package, so that may not be relevant. Conceivably the source code having a different node_modules than where tsc lives could make a difference?

Expected behavior:

After the first run, tsc uses tsBuildInfoFile to determine that packages/logger/src/index.ts is unchanged since the previous run, and finishes near-instantly.

Actual behavior:

It takes a full five seconds every time.

Some more info from using --diagnostics and --extendedDiagnostics:

Full command + output:

$ time npx tsc --incremental --diagnostics --extendedDiagnostics --tsBuildInfoFile packages/logger/buildinfo.json --outDir packages/logger/dist packages/logger/src/index.ts

Files:                         94
Lines:                      55069
Nodes:                     242144
Identifiers:                91394
Symbols:                   165716
Types:                      32500
Memory used:              163085K
Assignability cache size:   37419
Identity cache size:          174
Subtype cache size:             0
I/O Read time:              0.02s
Parse time:                 0.44s
Program time:               0.55s
Bind time:                  0.35s
Check time:                 1.58s
printTime time:             0.04s
Emit time:                  0.04s
transformTime time:         0.01s
commentTime time:           0.00s
I/O Write time:             0.00s
Total time:                 2.52s

real    0m2.884s
user    0m5.057s
sys     0m0.287s

Just for comparison, and to make sure it's not time or npx doing something bad:

$ time npx tsc --version

Version 3.7.0-dev.20190928

real    0m0.254s
user    0m0.209s
sys     0m0.041s

Playground Link:

N/A

Related Issues:

Maybe #30457

[mheiber]

I'm seeing the same thing on both Windows 10 with Git Bash and Red Hat Linux

Steps to reproduce

npm install -g typescript 3.6.3
git clone [email protected]/bloomberg/pasta-sourcemaps/
npm i
tsc --incremental --tsBuildInfoFile tsbuildinfo
time tsc --incremental --tsBuildInfoFile tsbuildinfo
rm tsbuildinfo
time tsc --incremental --tsBuildInfoFile tsbuildinfo

Actual Behavior:

Running repeatedly takes about the same amount of time with/without an existing tsbuildinfo file.

Expected Behavior:

compilation is faster with tsbuildinfo