dart-multiline-strings · diff
git:20260912.57dc63f to git:20260913.6c39005
61 added, 47 removed. Audit A to A.
---
name: dart-multiline-strings
description: |-
Guidelines and best practices for refactoring consecutive prints, single-line
string concatenations, and complex output blocks into triple-quoted multi-line
string literals (''' or """) in Dart.
license: Apache-2.0
key_features:
- Triple-quoted multiline strings
- Print & concatenation refactoring
- Formatting large text blocks
---
# Dart Multi-line Strings
## 1. When to use this skill
Use this skill when:
- - Refactoring consecutive `print()` or `stdout.writeln()` statements into a
- single, cohesive output block.
- - Simplifying string literals that span multiple lines, contain embedded
- newlines (`\n`), or use nested indentations.
- - Formatting large user-facing text output (like CLI help menus, reports, or
- templated messages) to be readable, maintainable, and performant.
+ - Refactoring consecutive `print()` or `stdout.writeln()` statements into a
+ single, cohesive output block.
+ - Simplifying string literals that span multiple lines, contain embedded
+ newlines (`\n`), or use nested indentations.
+ - Formatting large user-facing text output (like CLI help menus, reports, or
+ templated messages) to be readable, maintainable, and performant.
+
### When NOT to use (Abstention Guardrails)
Do NOT refactor to multiline strings when:
+
- **Short, Single-Line Outputs**: Strings that comfortably fit on a single line
(<80 chars) without embedded newlines.
- **Localized String Catalogs**: Strings that are looked up from localization
- bundles (e.g. `intl`, ARB files), where line breaks or formatting must
- conform to external translation tooling.
+ bundles (e.g. `intl`, ARB files), where line breaks or formatting must conform
+ to external translation tooling.
- **Raw Query Strings with Strict Whitespace Semantics**: Protocol strings,
strict CSV rows, or queries where indentation whitespace inside triple quotes
would alter payload semantics or introduce unintended leading spaces.
- **Streaming or Incremental I/O**: Progress bars, spinners, or interactive
console streams where individual writes occur with delays or flushing between
lines.
## Discovery
To find candidate code blocks for multi-line string refactoring:
- - Look for multiple back-to-back `print()` or `stdout.writeln()` calls inside
- a function, especially inside loops, console views, or CLI controllers.
- - Look for single-line strings heavily loaded with `\n` escape sequences.
- - Look for multiple string concatenations using the `+` operator or adjacent
- string literal splits that are meant to represent multi-line outputs.
+ - Look for multiple back-to-back `print()` or `stdout.writeln()` calls inside a
+ function, especially inside loops, console views, or CLI controllers.
+ - Look for single-line strings heavily loaded with `\n` escape sequences.
+ - Look for multiple string concatenations using the `+` operator or adjacent
+ string literal splits that are meant to represent multi-line outputs.
+
## 2. Guidelines
### Combine Consecutive Outputs
+
Instead of calling `print()` repeatedly for a multi-line output, group the
contents into a single triple-quoted string literal: `print('''...''')`.
### Explicit and Clean Alignment
+
In a triple-quoted literal, the exact spacing and formatting inside the quotes
are preserved. Use this to specify indentation levels visually instead of using
manually padded space prefixes (e.g., `' '`).
### Remove Empty Print Calls
+
If there are empty `print()` or `print('')` statements serving as vertical
- separators between output segments, replace them by letting the trailing
- newline of a multi-line string block handle the separation naturally.
+ separators between output segments, replace them by letting the trailing newline
+ of a multi-line string block handle the separation naturally.
### Handling the First Newline
+
If the opening triple-quote is immediately followed by a newline, the compiler
discards it.
- - If you do **not** want a leading blank line, start the string content on a
- fresh line in the source code for clean layout.
- - If you **do** want a leading blank line in the output, leave an extra empty
- line inside the triple-quoted block, or use `\n` explicitly at the
- beginning:
- ```dart
- print('''
- This starts with one blank line above it.''');
- ```
+ - If you do **not** want a leading blank line, start the string content on a
+ fresh line in the source code for clean layout.
+ - If you **do** want a leading blank line in the output, leave an extra empty
+ line inside the triple-quoted block, or use `\n` explicitly at the beginning:
+ ```dart
+ print('''
+ This starts with one blank line above it.''');
+ ```
+
### Handling the Trailing Newline & `print()`
+
`print()` automatically appends a trailing newline to the printed output.
- - If you place the closing `'''` on a new line (`\n''');`), an extra trailing
- blank line will be printed.
- - To avoid unintended trailing blank lines, place the closing triple-quotes
- immediately after the final character:
- ```dart
- // ✅ Emits standard output with no extra trailing empty line:
- print('''
- Header
- Content''');
- ```
+ - If you place the closing `'''` on a new line (`\n''');`), an extra trailing
+ blank line will be printed.
+ - To avoid unintended trailing blank lines, place the closing triple-quotes
+ immediately after the final character:
+ ```dart
+ // ✅ Emits standard output with no extra trailing empty line:
+ print('''
+ Header
+ Content''');
+ ```
+
### Avoiding Ghost Blank Lines in Conditional Interpolations
+
When injecting optional content via interpolation (`${condition ? '...' : ''}`),
placing the `${...}` on its own line leaves behind its enclosing newline when
the condition evaluates to `''`, producing an empty blank line in the output.
- - Include the leading newline *inside* the conditional string literal so the
- newline only renders when the content is present:
- ```dart
- // ✅ Clean conditional rendering without ghost blank lines:
- print('''
- Branch Details:
- Name: $branch${hasWarning ? '\n WARNING: $warningMessage' : ''}''');
- ```
+ - Include the leading newline _inside_ the conditional string literal so the
+ newline only renders when the content is present:
+ ```dart
+ // ✅ Clean conditional rendering without ghost blank lines:
+ print('''
+ Branch Details:
+ Name: $branch${hasWarning ? '\n WARNING: $warningMessage' : ''}''');
+ ```
+
### 80-Character Line Limit Exemption
- The `lines_longer_than_80_chars` lint rule **automatically ignores** lines inside
- multiline string literals. You can write long lines inside triple-quotes without
- triggering linter warnings or being forced to break them up.
+ The `lines_longer_than_80_chars` lint rule **automatically ignores** lines
+ inside multiline string literals. You can write long lines inside triple-quotes
+ without triggering linter warnings or being forced to break them up.
+
### Dynamic Switch Expressions inside Interpolation
+
Leverage Dart 3 switch expressions directly inside string interpolations to
dynamically select and inject optional lines, conditional labels, or helper
instructions. This avoids cluttering the surrounding code with imperatively
constructed strings or multiple `if` statements:
+
```dart
print('''
Status: ${status.isSuccess ? 'PASS' : 'FAIL'}${switch (status) {
Status.failed => '\nError details: $errorMessage',
_ => '',
}}''');
```
## 3. Examples
### Refactoring Consecutive Prints with Indentation
**Avoid:**
+
```dart
void printGerritView(String branch, String desc, bool hasConflicts) {
print('Branch Details:');
print(' Name: ' + branch);
print(' Description: ' + desc);
print('');
if (hasConflicts) {
print(' WARNING: This branch has conflicts.');
print(' Run `git merge origin/main` to resolve.');
}
}
```
**Prefer:**
+
```dart
void printGerritView(String branch, String desc, bool hasConflicts) {
print('''
Branch Details:
Name: $branch
Description: $desc${hasConflicts ? '''
WARNING: This branch has conflicts.
Run `git merge origin/main` to resolve.''' : ''}''');
}
```
-
-