Diagnostics

A diagnostic of the compiler has a code, a severity, and a position. This chapter explains how to read one, how to look up its code, and how to change its severity for a project.

Read a diagnostic

error[E037]: Invalid assignment: cannot assign 'STRING' to 'DINT'
  ┌─ main.st:6:5
  │
6 │     x := 'text';
  │     ^^^^^^^^^^^ Invalid assignment: cannot assign 'STRING' to 'DINT'

error: Compilation aborted due to critical errors.
Hint: You can use `plc explain <ErrorCode>` for more information

The first line gives the severity, the code, and the problem. The second gives the position: the compiler writes the path of the file in full, and the examples in this book shorten it to the file name. The marker under the source line shows the part of the statement that the message is about.

The compiler collects the diagnostics of a stage before it stops, so one run usually reports more than one problem. An error stops the run before code generation. A warning and an information message do not.

Look up a code

plc explain E037

The command prints the explanation of the code: usually a description with an example of the mistake and of the correct form, and for a part of the codes a title and nothing more. It works without a project, and the error code reference has the same text.

Severity

A diagnostic has one of four severities:

Severity	Effect
`error`	Reported, and the run stops after the stage
`warning`	Reported, the run continues
`info`	Reported, the run continues
`ignore`	Not reported

plc config diagnostics prints the severity of every code as JSON:

{"ignore":["E132","E015"],"warning":["E096","E042", ...],"info":["E092", ...],"error":["E119", ...]}

Change the severity

Write the codes you want to move into a file, with the severity as the key:

{
    "warning": [ "E037" ],
    "ignore":  [ "E023" ]
}

plc --check main.st --error-config severities.json

E037 is now a warning, so the run continues and the exit code stays 0. A code that you do not name keeps its default severity.

The option is global, so it works with build and check as well. To see the result of your file, print the merged configuration:

plc config diagnostics --error-config severities.json

Output format

Value	Output
`rich`	The default. Source snippet, position marker, and color
`clang`	One line per diagnostic, in the format of `clang`, for tools that parse it
`none`	No messages. A run that fails still reports that it was aborted

plc --check main.st --error-format=clang

main.st:6:5:{6:5-6:16}: error[E037]: Invalid assignment: cannot assign 'STRING' to 'DINT'
error: Compilation aborted due to critical errors

What’s next

The error code reference has a page per code, with an example of the mistake and of the correct form. The next chapter is about the information that the compiler puts into the artifact for a debugger.

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