sqruff_lib/rules/aliasing/
al04.rs

use std::fmt::Debug;

use ahash::{AHashMap, AHashSet};
use smol_str::SmolStr;
use sqruff_lib_core::dialects::common::{AliasInfo, ColumnAliasInfo};
use sqruff_lib_core::dialects::syntax::{SyntaxKind, SyntaxSet};
use sqruff_lib_core::helpers::IndexSet;
use sqruff_lib_core::parser::segments::object_reference::ObjectReferenceSegment;
use sqruff_lib_core::utils::analysis::select::get_select_statement_info;

use crate::core::config::Value;
use crate::core::rules::base::{Erased, ErasedRule, LintResult, Rule, RuleGroups};
use crate::core::rules::context::RuleContext;
use crate::core::rules::crawlers::{Crawler, SegmentSeekerCrawler};

type Handle<T> = fn(
    Vec<AliasInfo>,
    Vec<SmolStr>,
    Vec<ObjectReferenceSegment>,
    Vec<ColumnAliasInfo>,
    Vec<SmolStr>,
    &T,
) -> Vec<LintResult>;

#[derive(Debug, Clone)]
pub struct RuleAL04<T = ()> {
    pub(crate) lint_references_and_aliases: Handle<T>,
    pub(crate) context: T,
}

impl Default for RuleAL04 {
    fn default() -> Self {
        RuleAL04 {
            lint_references_and_aliases: Self::lint_references_and_aliases,
            context: (),
        }
    }
}

impl<T: Clone + Debug + Send + Sync + 'static> Rule for RuleAL04<T> {
    fn load_from_config(&self, _config: &AHashMap<String, Value>) -> Result<ErasedRule, String> {
        Ok(RuleAL04::default().erased())
    }

    fn name(&self) -> &'static str {
        "aliasing.unique.table"
    }

    fn description(&self) -> &'static str {
        "Table aliases should be unique within each clause."
    }

    fn long_description(&self) -> &'static str {
        r#"
**Anti-pattern**

In this example, the alias t is reused for two different tables:

```sql
SELECT
    t.a,
    t.b
FROM foo AS t, bar AS t

-- This can also happen when using schemas where the
-- implicit alias is the table name:

SELECT
    a,
    b
FROM
    2020.foo,
    2021.foo
```

**Best practice**

Make all tables have a unique alias.

```sql
SELECT
    f.a,
    b.b
FROM foo AS f, bar AS b

-- Also use explicit aliases when referencing two tables
-- with the same name from two different schemas.

SELECT
    f1.a,
    f2.b
FROM
    2020.foo AS f1,
    2021.foo AS f2
```
"#
    }

    fn groups(&self) -> &'static [RuleGroups] {
        &[RuleGroups::All, RuleGroups::Core, RuleGroups::Aliasing]
    }

    fn eval(&self, context: RuleContext) -> Vec<LintResult> {
        let Some(select_info) =
            get_select_statement_info(&context.segment, context.dialect.into(), true)
        else {
            return Vec::new();
        };

        let _parent_select = context
            .parent_stack
            .iter()
            .rev()
            .find(|seg| seg.is_type(SyntaxKind::SelectStatement));

        (self.lint_references_and_aliases)(
            select_info.table_aliases,
            select_info.standalone_aliases,
            select_info.reference_buffer,
            select_info.col_aliases,
            select_info.using_cols,
            &self.context,
        )
    }

    fn crawl_behaviour(&self) -> Crawler {
        SegmentSeekerCrawler::new(const { SyntaxSet::new(&[SyntaxKind::SelectStatement]) }).into()
    }
}

impl RuleAL04 {
    pub fn lint_references_and_aliases(
        table_aliases: Vec<AliasInfo>,
        _: Vec<SmolStr>,
        _: Vec<ObjectReferenceSegment>,
        _: Vec<ColumnAliasInfo>,
        _: Vec<SmolStr>,
        _: &(),
    ) -> Vec<LintResult> {
        let mut duplicates = IndexSet::default();
        let mut seen: AHashSet<_> = AHashSet::new();

        for alias in table_aliases.iter() {
            if !seen.insert(&alias.ref_str) && !alias.ref_str.is_empty() {
                duplicates.insert(alias);
            }
        }

        duplicates
            .into_iter()
            .map(|alias| {
                LintResult::new(
                    alias.segment.clone(),
                    Vec::new(),
                    None,
                    format!(
                        "Duplicate table alias '{}'. Table aliases should be unique.",
                        alias.ref_str
                    )
                    .into(),
                    None,
                )
            })
            .collect()
    }
}
sqruff_lib/rules/aliasing/al04.rs

sqruff_lib/rules/aliasing/
al04.rs
