Check if printing to a terminal for color output

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ## **[Unreleased]**
 
-- [#1147](https://github.com/wasmerio/wasmer/pull/1147) Remove `log` and `trace` macros from `wasmer-runtime-core`, remove `debug` and `trace` features from `wasmer-*` crates, use the `log` crate for logging and use `fern` in the Wasmer CLI binary to output log messages.  To disable colorized output, set the `WASMER_DISABLE_COLOR` environment variable.
+- [#1147](https://github.com/wasmerio/wasmer/pull/1147) Remove `log` and `trace` macros from `wasmer-runtime-core`, remove `debug` and `trace` features from `wasmer-*` crates, use the `log` crate for logging and use `fern` in the Wasmer CLI binary to output log messages.  Colorized output will be enabled automatically if printing to a terminal, to force colorization on or off, set the `WASMER_COLOR` environment variable to `true` or `false`.
 - [#1128](https://github.com/wasmerio/wasmer/pull/1128) Fix a crash when a host function is missing and the `allow_missing_functions` flag is enabled
 - [#1099](https://github.com/wasmerio/wasmer/pull/1099) Remove `backend::Backend` from `wasmer_runtime_core`
 - [#1097](https://github.com/wasmerio/wasmer/pull/1097) Move inline breakpoint outside of runtime backend

Cargo.toml

@@ -20,6 +20,7 @@ include = [
 ]
 
 [dependencies]
+atty = "0.2"
 byteorder = "1.3"
 errno = "0.2"
 fern = { version = "0.5", features = ["colored"], optional = true }

Makefile

@@ -231,30 +231,30 @@ check: check-bench
 	cargo check --release --manifest-path lib/runtime/Cargo.toml
 
 	$(RUNTIME_CHECK) \
-		--features=cranelift,cache,debug,llvm,singlepass,default-backend-singlepass
+		--features=cranelift,cache,llvm,singlepass,default-backend-singlepass
 	$(RUNTIME_CHECK) --release \
 		--features=cranelift,cache,llvm,singlepass,default-backend-singlepass
 	$(RUNTIME_CHECK) \
-		--features=cranelift,cache,debug,llvm,singlepass,default-backend-cranelift
+		--features=cranelift,cache,llvm,singlepass,default-backend-cranelift
 	$(RUNTIME_CHECK) --release \
 		--features=cranelift,cache,llvm,singlepass,default-backend-cranelift
 	$(RUNTIME_CHECK) \
-		--features=cranelift,cache,debug,llvm,singlepass,default-backend-llvm
+		--features=cranelift,cache,llvm,singlepass,default-backend-llvm
 	$(RUNTIME_CHECK) --release \
 		--features=cranelift,cache,llvm,singlepass,default-backend-llvm
 	$(RUNTIME_CHECK) \
-		--features=singlepass,default-backend-singlepass,debug
+		--features=singlepass,default-backend-singlepass
 	$(RUNTIME_CHECK) --release \
 		--features=singlepass,default-backend-singlepass
 	$(RUNTIME_CHECK) \
-		--features=cranelift,default-backend-cranelift,debug
+		--features=cranelift,default-backend-cranelift
 	$(RUNTIME_CHECK) --release \
 		--features=cranelift,default-backend-cranelift
 	$(RUNTIME_CHECK) \
-		--features=llvm,default-backend-llvm,debug
+		--features=llvm,default-backend-llvm
 	$(RUNTIME_CHECK) --release \
 		--features=llvm,default-backend-llvm
-		--features=default-backend-singlepass,singlepass,cranelift,llvm,cache,debug,deterministic-execution
+		--features=default-backend-singlepass,singlepass,cranelift,llvm,cache,deterministic-execution
 
 # Release
 release:

src/utils.rs

@@ -122,7 +122,8 @@ pub fn parse_args(
 
 /// Whether or not Wasmer should print with color
 pub fn wasmer_should_print_color() -> bool {
-    std::env::var("WASMER_DISABLE_COLOR")
-        .map(|_| false)
-        .unwrap_or(true)
+    std::env::var("WASMER_COLOR")
+        .ok()
+        .and_then(|inner| inner.parse::<bool>().ok())
+        .unwrap_or(atty::is(atty::Stream::Stdout))
 }