Tracing

The TypeSpec Compiler, by default, builds without any debug information. The standard output is minimal, only including any warning or error diagnostics that occur during the compilation process.

However, the compiler does collect additional information that can be accessed using the --trace command-line interface (CLI) flag.

tsp compile . --trace import-resolution

If you want to log multiple areas, you can use the --trace option more than once.

tsp compile . --trace import-resolution --trace projection

To log everything, use --trace * or --debug but note this might produce a significant output.

You can also specify the trace areas in the tspconfig.yaml file:

tspconfig.yaml

trace: *

trace:
  - import-resolution
  - projection

Selecting trace areas

The tracing system in the tsp compiler organizes each trace under a specific area. The area name is a dot . separated string of area segments.

To filter the areas you want to trace, you can use this area path. The filter follows the same naming style, but the last segment can be a wildcard *. However, this produces the same result as leaving out the last segment. In other words, these filters behave identically:

• foo and foo.*
• one.two and one.two.*

For instance, if we have these three areas:

• one.two.three
• one.foo
• bar.info

You can use:

• * to log everything
• one to log everything under one(one.two.three, one.foo)
• bar to log everything under bar(bar.info)
• one.foo to log everything under one.foo(one.foo)
• other to log everything under other, which is nothing in this case.

Trace areas in the compiler

Here is a list of the trace areas used in the compiler:

Area	Description
compiler.options	Logs the resolved compiler options
import-resolution.library	Logs information related to the resolution of import libraries
projection.log	Logs debug information from the log() function used in projections
bind.js	Logs information when binding JS files
linter.register-library	Logs information when a library’s rules are being loaded
linter.register-library.rule	Logs information about a rule that is being registered
linter.extend-rule-set.start	Logs information about a ruleset that is about to be extended
linter.extend-rule-set.end	Logs information about rules enabled after extending a ruleset
linter.lint	Starts the lint process and shows information of all the rules enabled

ApiTracing in TypeSpec libraries

TypeSpec libraries can also emit their own traces that can be collected using the same mechanism. To avoid naming conflicts, it’s recommended that a library prefixes their tracing area with the library name. This can be done by calling the sub(subArea: string) method on the tracer.

const tracer = program.tracer.sub("my-library");

The tracer can then be used for trace collection:

tracer.trace("emitting-ts", "Emitting ts interface");