100 Unhandled root runtime error

A root expression is fallible and its runtime error isn’t handled in the DPL program.

Rationale

DPL is fail safe and thus requires that all possible runtime errors be handled. This provides important safety guarantees to DPL and helps to ensure that DPL programs run reliably when deployed.

Resolution

Handle the runtime error by assigning, coalescing, or raising the error.

Examples

get_env_var("HOST")

- 	get_env_var("HOST")
+# 	.host = get_env_var("HOST")

101 Malformed regex literal

A regex literal expression is malformed and thus doesn’t result in a valid regular expression.

Rationale

Invalid regular expressions don’t compile.

Resolution

Regular expressions are difficult to write and commonly result in syntax errors. If you’re parsing a common log format we recommend using one of DPL’s parse_* functions. If you don’t see a function for your format please request it. Otherwise, use the Rust regex tester to test and correct your regular expression.

Examples

. |= parse_regex!(.message, r'^(?P<host>[\w\.]+) - (?P<user>[\w]+) (?P<bytes_in>[\d]+) \[?P<timestamp>.*)\] "(?P<method>[\w]+) (?P<path>.*)" (?P<status>[\d]+) (?P<bytes_out>[\d]+)$')

-. |= parse_regex!(.message, r'^(?P<host>[\w\.]+) - (?P<user>[\w]+) (?P<bytes_in>[\d]+) \[?P<timestamp>.*)\] "(?P<method>[\w]+) (?P<path>.*)" (?P<status>[\d]+) (?P<bytes_out>[\d]+)$')
+. |= parse_common_log!(.message)

102 Non-boolean if expression predicate

An if expression predicate doesn’t evaluate to a Boolean.

Rationale

DPL doesn’t implement “truthy” values (non-Boolean values that resolve to a Boolean, such as 1) since these are common foot-guns that can result in unexpected behavior when used in if expressions. This provides important safety guarantees in DPL and ensures that DPL programs are reliable once deployed.

Resolution

Adjust your if expression predicate to resolve to a Boolean. Helpful functions to solve this include exists and is_nullish.

Examples

if .message {
	. |= parse_key_value!(.message)
}

-if .message {
+if exists(.message) {
 	. |= parse_key_value!(.message)
 }

103 Unhandled fallible assignment

The right-hand side of this assignment is fallible (that is, it can produce a runtime error), but the error isn’t handled.

Rationale

DPL is fail safe and thus requires that all possible runtime errors be handled. This provides important safety guarantees to DPL and helps to ensure that DPL programs run reliably when deployed.

Resolution

Handle the runtime error by either assigning it, coalescing it, or raising it.

Examples

. = parse_key_value(.message)

-. = parse_key_value(.message)
+. = parse_key_value(.message) ?? {}

. = parse_key_value(.message)

-. = parse_key_value(.message)
+. = parse_key_value!(.message)

. = parse_key_value(.message)

-. = parse_key_value(.message)
+., err = parse_key_value(.message)

104 Unnecessary error assignment

The left-hand side of an assignment expression needlessly handles errors even though the right-hand side can’t fail.

Rationale

Assigning errors when one is not possible is effectively dead code that makes your program difficult to follow. Removing the error assignment simplifies your program.

Resolution

Remove the error assignment.

Examples

.message, err = downcase(.message)

-.message, err = downcase(.message)
+.message = downcase(.message)

105 Undefined function

A function call expression invokes an unknown function.

Resolution

This is typically due to a typo. Correcting the function name should resolve this.

Examples

parse_keyvalue(.message)

-parse_keyvalue(.message)
+parse_key_value(.message)

106 Function argument arity mismatch

A function call expression invokes a function with too many arguments.

Resolution

Remove the extra arguments to adhere to the function’s documented signature.

Examples

parse_json(.message, pretty: true)

-parse_json(.message, pretty: true)
+parse_json(.message)

107 Required function argument missing

A function call expression fails to pass a required argument.

Resolution

Supply all of the required function arguments to adhere to the function’s documented signature.

Examples

parse_timestamp(.timestamp)

-parse_timestamp(.timestamp)
+parse_timestamp(.timestamp, format: "%D")

108 Unknown function argument keyword

A function call expression passes an unknown named argument.

Resolution

Correct the name to align with the documented argument names for the function.

Examples

parse_timestamp(.timestamp, fmt: "%D")

-parse_timestamp(.timestamp)
+parse_timestamp(.timestamp, format: "%D")

110 Invalid argument type

An argument passed to a function call expression isn’t a supported type.

Rationale

DPL is fail safe and thus requires that all possible runtime errors be handled. This provides important safety guarantees to DPL and helps to ensure that DPL programs run reliably when deployed.

Resolution

You must guarantee the type of the variable by using the appropriate type or coercion function.

Examples

downcase(.message)

+.message = string(.message) ?? ""
 downcase(.message)

downcase(.message)

downcase(string!(.message))

111 Unhandled predicate error

A predicate is fallible and its runtime error isn’t handled in the DPL program.

Rationale

DPL is fail safe and thus requires that all possible runtime errors be handled. This provides important safety guarantees to DPL and helps to ensure that DPL programs run reliably when deployed.

Resolution

Handle the runtime error by assigning, coalescing, or raising the error.

Examples

if contains(.field, "thing") {
  log("thing")
}

-       if contains(.field, "thing") {
+#      if contains(.field, "thing") ?? false {

203 Unrecognized token

Your DPL program contains a token (character) that the DPL parser doesn’t recognize as valid.

Resolution

Use a valid token.

Examples

😂

-😂
+"some valid value"

204 Unrecognized end-of-file (EOF)

The DPL parser has reached the end of the program in an invalid state, potentially due to a typo or a dangling expression.

Resolution

Make sure that the last expression in the program is valid.

Examples

.field1 = "value1"
.field2 =

-.bar =
+.field2 = "value2"

205 Reserved keyword

You’ve used a name for a variable that serves another purpose in DPL or is reserved for potential future use.

Resolution

Use a different variable name.

Examples

else = "some value"

-else = "some value"
+some_non_reserved_name = "some value"

206 Invalid numeric literal

The DPL compiler doesn’t recognize this numeric literal as valid.

207 Invalid string literal

Your DPL program contains a string literal that the DPL parser doesn’t recognize as valid.

Resolution

Make sure that your string is properly enclosed by single or double quotes.

Examples

"Houston, we have a problem'

- "Houston, we have a problem'
+ "Houston, we have a problem"

208 Invalid literal

The DPL compiler doesn’t recognize this literal value as valid.

209 Invalid escape character

Your string includes an escape character that the DPL compiler doesn’t recognize as valid

300 Unexpected type

The DPL compiler expected a value of a specific type but found a different type.

301 Type coercion error

This value can’t be coerced into the desired type.

302 Remainder error

These two types can’t produce a remainder.

303 Multiplication error

These types can’t be multiplied together

304 Division error

The left-hand value can’t be divided by the right-hand value.

305 Divide by zero

You’ve attempted to divide an integer or float by zero.

Rationale

Unlike some other programming languages, DPL doesn’t have any concept of infinity, as it’s unclear how that could be germane to observability data use cases. Thus, dividing by zero can’t have any meaningful result.

Resolution

If you know that a value is necessarily zero, don’t divide by it. If a value could be zero, capture the potential error thrown by the operation:

result, err = 27 / .some_value
if err != nil {
	# Handle error
}

306 NaN float

Floats in DPL can’t be NaN (not a number).

307 Addition error

These two values can’t be added together.

308 Subtraction error

The right-hand value can’t be subtracted from the left-hand value.

309 Or expression error

These two values can’t be combined into an or expression.

310 And expression error

These two values can’t be combined into an and expression.

311 Greater than error

These two values can’t be used in a greater than expression.

312 Greater than or equal to error

These two values can’t be used in a greater than or equal to expression.

313 Less than error

These two values can’t be used in less than expression.

314 Less than or equal to error

These two values can’t be used in a less than or equal to expression.

315 mutation of read-only value

This value is read-only and cannot be deleted or mutated.

400 Unexpected expression

The DPL compiler encountered an expression type that wasn’t expected here.

401 Invalid enum variant

DPL expects an enum value for this argument, but the value you entered for the enum is invalid.

Resolution

Check the documentation for this function in the DPL functions reference to see which enum values are valid for this argument.

402 Expected static expression for function argument

DPL expected a static expression for a function argument, but a dynamic one was provided (such as a variable).

DPL requires static expressions for some function arguments to validate argument types at compile time to avoid runtime errors.

Resolution

Replace the dynamic argument with a static expression.

403 Invalid argument

An invalid argument was passed to the function. The error string will contain more details about what was invalid.

Resolution

Check the error string for this error to see what was invalid.

601 Invalid timestamp

The provided timestamp literal is properly formed (i.e. it uses t'...' syntax) but the timestamp doesn’t adhere to RFC 3339 format.

Rationale

Invalid timestamps don’t compile.

Resolution

Bring the timestamp in conformance with RFC 3339 format.

Examples

.timestamp = format_timestamp!(t'next Tuesday', format: "%v %R")

-.timestamp = format_timestamp!(t'next Tuesday', format: "%v %R")
+.timestamp = format_timestamp!(t'2021-03-09T16:33:02.405806Z', format: "%v %R")

620 Aborting infallible function

You’ve specified that a function should abort on error even though the function is infallible.

Rationale

In DPL, infallible functions—functions that can’t fail—don’t require error handling, which in turn means it doesn’t make sense to abort on failure using a ! in the function call.

Resolution

Remove the ! from the function call.

Examples

encode_json!(["one", "two", "three"])

- 	encode_json!(["one", "two", "three"])
+# 	encode_json(["one", "two", "three"])

630 Fallible argument

You’ve passed a fallible expression as an argument to a function.

Rationale

In DPL, expressions that you pass to functions as arguments need to be infallible themselves. Otherwise, the outcome of the function would be indeterminate.

Resolution

Make the expression passed to the function infallible, potentially by aborting on error using !, coalescing the error using ??, or via some other method.

Examples

format_timestamp!(to_timestamp("2021-01-17T23:27:31.891948Z"), format: "%v %R")

- 	format_timestamp!(to_timestamp("2021-01-17T23:27:31.891948Z"), format: "%v %R")
+ 	format_timestamp!(to_timestamp!("2021-01-17T23:27:31.891948Z"), format: "%v %R")

631 Fallible abort message expression

You’ve passed a fallible expression as a message to abort.

Rationale

An expression that you pass to abort needs to be infallible. Otherwise, the abort expression could fail at runtime.

Resolution

Make the expression infallible, potentially by handling the error, coalescing the error using ??, or via some other method.

Examples

abort to_syslog_level(0)

- abort to_syslog_level(0)
+ abort to_syslog_level(0) ?? "other"

640 No-op assignment

You’ve assigned a value to something that is neither a variable nor a path.

Rationale

All assignments in DPL need to be to either a path or a variable. If you try to assign a value to, for example, underscore (_), this operation is considered a “no-op” as it has no effect (and is thus not an assignment at all).

Resolution

Assign the right-hand-side value to either a variable or a path.

Examples

_ = "the hills are alive"

- 	_ = "the hills are alive"
+# 	.movie_song_quote = "the hills are alive"

650 Chained comparison operators

You’ve chained multiple comparison operators together in a way that can’t result in a valid expression.

Rationale

Comparison operators can only operate on two operands, e.g. 1 != 2. Chaining them together, as in 1 < 2 < 3, produces a meaningless non-expression.

Resolution

Use comparison operators only on a left-hand- and a right-hand-side value. You can chain comparisons together provided that the expressions are properly grouped. While a == b == c, for example, isn’t valid, a == b && b == c is valid because it involves distinct Boolean expressions.

Examples

1 == 1 == 2

- 	1 == 1 == 2
+# 	(1 == 1) && (1 == 2)

651 Unnecessary error coalescing operation

You’ve used a coalescing operation (??) to handle an error, but in this case the left-hand operation is infallible, and so the right-hand value after ?? is never reached.

Rationale

Error coalescing operations are useful when you want to specify what happens if an operation fails. Here’s an example:

result = op1 ?? op2

In this example, if op1 is infallible (that is, it can’t error) then the result variable if set to the value of op1 while op2 is never reached.

Resolution

If the left-hand operation is meant to be infallible, remove the ?? operator and the right-hand operation. If, however, the left-hand operation is supposed to be fallible, remove the ! from the function call and anything else that’s making it infallible.

652 Only objects can be merged

You’re attempting to merge two values together but one or both isn’t an object.

Rationale

Amongst DPL’s available types, only objects can be merged together. It’s not clear what it would mean to merge, for example, an object with a Boolean. Please note, however, that some other DPL types do have merge-like operations available:

• Strings can be concatenated together
• Arrays can be appended to other arrays

These operations may come in handy if you’ve used merge by accident.

Resolution

Make sure that both values that you’re merging are DPL objects. If you’re not sure whether a value is an object, you can use the object function to check.

660 Non-Boolean negation

You’ve used the negation operator to negate a non-Boolean expression.

Rationale

Only Boolean values can be used with the negation operator (!). The expression !false, for example, produces true, whereas !"hello" is a meaningless non-expression.

Resolution

Use the negation operator only with Boolean expressions.

Examples

!47

- 	!47
+# 	!(47 == 48)

701 Call to Undefined Variable

The referenced variable is undefined.

Rationale

Referencing a variable that is undefined results in unexpected behavior, and is likely due to a typo.

Resolution

Assign the variable first, or resolve the reference typo.

Examples

my_variable

+my_variable = true
my_variable

my_variable = true
my_var

-my_var
+my_variable

801 Usage of deprecated item

The referenced item is deprecated. Usually an alternative is given that can be used instead.

Rationale

This will be removed in the future.

Resolution

Apply the suggested alternative.