Accept TF_LOG=json to enable TRACE logs in JSON format

This is not currently a supported interface, but we plan to release
tool(s) that consume parts of it that are more dependable later,
separately from Terraform CLI itself.

internal/logging/logging.go

@@ -81,7 +81,7 @@ func HCLogger() hclog.Logger {
 // newHCLogger returns a new hclog.Logger instance with the given name
 func newHCLogger(name string) hclog.Logger {
 	logOutput := io.Writer(os.Stderr)
-	logLevel := globalLogLevel()
+	logLevel, json := globalLogLevel()
 
 	if logPath := os.Getenv(envLogFile); logPath != "" {
 		f, err := os.OpenFile(logPath, syscall.O_CREAT|syscall.O_RDWR|syscall.O_APPEND, 0666)
@@ -97,6 +97,7 @@ func newHCLogger(name string) hclog.Logger {
 		Level:             logLevel,
 		Output:            logOutput,
 		IndependentLevels: true,
+		JSONFormat:        json,
 	})
 }
 
@@ -127,7 +128,8 @@ func NewProviderLogger(prefix string) hclog.Logger {
 
 // CurrentLogLevel returns the current log level string based the environment vars
 func CurrentLogLevel() string {
-	return strings.ToUpper(globalLogLevel().String())
+	ll, _ := globalLogLevel()
+	return strings.ToUpper(ll.String())
 }
 
 func providerLogLevel() hclog.Level {
@@ -139,19 +141,25 @@ func providerLogLevel() hclog.Level {
 	return parseLogLevel(providerEnvLevel)
 }
 
-func globalLogLevel() hclog.Level {
+func globalLogLevel() (hclog.Level, bool) {
+	var json bool
 	envLevel := strings.ToUpper(os.Getenv(envLog))
 	if envLevel == "" {
 		envLevel = strings.ToUpper(os.Getenv(envLogCore))
-
 	}
-	return parseLogLevel(envLevel)
+	if envLevel == "JSON" {
+		json = true
+	}
+	return parseLogLevel(envLevel), json
 }
 
 func parseLogLevel(envLevel string) hclog.Level {
 	if envLevel == "" {
 		return hclog.Off
 	}
+	if envLevel == "JSON" {
+		envLevel = "TRACE"
+	}
 
 	logLevel := hclog.Trace
 	if isValidLogLevel(envLevel) {
@@ -166,7 +174,7 @@ func parseLogLevel(envLevel string) hclog.Level {
 
 // IsDebugOrHigher returns whether or not the current log level is debug or trace
 func IsDebugOrHigher() bool {
-	level := globalLogLevel()
+	level, _ := globalLogLevel()
 	return level == hclog.Debug || level == hclog.Trace
 }
 

website/docs/internals/debugging.html.md

@@ -12,6 +12,10 @@ Terraform has detailed logs which can be enabled by setting the `TF_LOG` environ
 
 You can set `TF_LOG` to one of the log levels `TRACE`, `DEBUG`, `INFO`, `WARN` or `ERROR` to change the verbosity of the logs.
 
+Setting `TF_LOG` to `JSON` outputs logs at the `TRACE` level or higher, and uses a parseable JSON encoding as the formatting.
+
+~> **Warning:** The JSON encoding of log files is not considered a stable interface. It may change at any time, without warning. It is meant to support tooling that will be forthcoming, and that tooling is the only supported way to interact with JSON formatted logs.
+
 Logging can be enabled separately for terraform itself and the provider plugins
 using the `TF_LOG_CORE` or `TF_LOG_PROVIDER` environment variables. These take
 the same level arguments as `TF_LOG`, but only activate a subset of the logs.