Doc gen: Migrate aggregate functions doc to attribute based. (#13646)

* Doc gen: Migrate aggregate functions doc to attribute based.

datafusion/core/src/bin/print_functions_docs.rs

@@ -84,6 +84,29 @@ fn print_window_docs() -> Result<String> {
     print_docs(providers, window_doc_sections::doc_sections())
 }
 
+// Temporary method useful to semi automate
+// the migration of UDF documentation generation from code based
+// to attribute based
+// To be removed
+fn save_doc_code_text(documentation: &Documentation, name: &str) {
+    let attr_text = documentation.to_doc_attribute();
+
+    let file_path = format!("{}.txt", name);
+    if std::path::Path::new(&file_path).exists() {
+        std::fs::remove_file(&file_path).unwrap();
+    }
+
+    // Open the file in append mode, create it if it doesn't exist
+    let mut file = std::fs::OpenOptions::new()
+        .append(true) // Open in append mode
+        .create(true) // Create the file if it doesn't exist
+        .open(file_path)
+        .unwrap();
+
+    use std::io::Write;
+    file.write_all(attr_text.as_bytes()).unwrap();
+}
+
 fn print_docs(
     providers: Vec<Box<dyn DocProvider>>,
     doc_sections: Vec<DocSection>,
@@ -158,6 +181,9 @@ fn print_docs(
                 unreachable!()
             };
 
+            // Temporary for doc gen migration, see `save_doc_code_text` comments
+            save_doc_code_text(documentation, &name);
+
             // first, the name, description and syntax example
             let _ = write!(
                 docs,

datafusion/doc/src/lib.rs

@@ -63,6 +63,90 @@ impl Documentation {
     ) -> DocumentationBuilder {
         DocumentationBuilder::new(doc_section, description, syntax_example)
     }
+
+    /// Output the `Documentation` struct in form of custom Rust documentation attributes
+    /// It is useful to semi automate during tmigration of UDF documentation
+    /// generation from code based to attribute based and can be safely removed after
+    pub fn to_doc_attribute(&self) -> String {
+        let mut result = String::new();
+
+        result.push_str("#[user_doc(");
+        // Doc Section
+        result.push_str(
+            format!(
+                "\n    doc_section({}label = \"{}\"{}),",
+                if !self.doc_section.include {
+                    "include = \"false\", "
+                } else {
+                    ""
+                },
+                self.doc_section.label,
+                self.doc_section
+                    .description
+                    .map(|s| format!(", description = \"{}\"", s))
+                    .unwrap_or_default(),
+            )
+            .as_ref(),
+        );
+
+        // Description
+        result.push_str(format!("\n    description=\"{}\",", self.description).as_ref());
+        // Syntax Example
+        result.push_str(
+            format!("\n    syntax_example=\"{}\",", self.syntax_example).as_ref(),
+        );
+        // SQL Example
+        result.push_str(
+            &self
+                .sql_example
+                .clone()
+                .map(|s| format!("\n    sql_example = r#\"{}\"#,", s))
+                .unwrap_or_default(),
+        );
+
+        let st_arg_token = " expression to operate on. Can be a constant, column, or function, and any combination of operators.";
+        // Standard Arguments
+        if let Some(args) = self.arguments.clone() {
+            args.iter().for_each(|(name, value)| {
+                if value.contains(st_arg_token) {
+                    if name.starts_with("The ") {
+                        result.push_str(format!("\n    standard_argument(\n        name = \"{}\"),", name).as_ref());
+                    } else {
+                        result.push_str(format!("\n    standard_argument(\n        name = \"{}\",\n        prefix = \"{}\"\n    ),", name, value.replace(st_arg_token, "")).as_ref());
+                    }
+                }
+            });
+        }
+
+        // Arguments
+        if let Some(args) = self.arguments.clone() {
+            args.iter().for_each(|(name, value)| {
+                if !value.contains(st_arg_token) {
+                    result.push_str(format!("\n    argument(\n        name = \"{}\",\n        description = \"{}\"\n    ),", name, value).as_ref());
+                }
+            });
+        }
+
+        if let Some(alt_syntax) = self.alternative_syntax.clone() {
+            alt_syntax.iter().for_each(|syntax| {
+                result.push_str(
+                    format!("\n    alternative_syntax = \"{}\",", syntax).as_ref(),
+                );
+            });
+        }
+
+        // Related UDFs
+        if let Some(related_udf) = self.related_udfs.clone() {
+            related_udf.iter().for_each(|udf| {
+                result
+                    .push_str(format!("\n    related_udf(name = \"{}\"),", udf).as_ref());
+            });
+        }
+
+        result.push_str("\n)]");
+
+        result
+    }
 }
 
 #[derive(Debug, Clone, PartialEq)]

datafusion/functions-aggregate/Cargo.toml

@@ -42,9 +42,11 @@ ahash = { workspace = true }
 arrow = { workspace = true }
 arrow-schema = { workspace = true }
 datafusion-common = { workspace = true }
+datafusion-doc = { workspace = true }
 datafusion-execution = { workspace = true }
 datafusion-expr = { workspace = true }
 datafusion-functions-aggregate-common = { workspace = true }
+datafusion-macros = { workspace = true }
 datafusion-physical-expr = { workspace = true }
 datafusion-physical-expr-common = { workspace = true }
 half = { workspace = true }

datafusion/functions-aggregate/src/approx_distinct.rs

@@ -31,17 +31,19 @@ use datafusion_common::ScalarValue;
 use datafusion_common::{
     downcast_value, internal_err, not_impl_err, DataFusionError, Result,
 };
-use datafusion_expr::aggregate_doc_sections::DOC_SECTION_APPROXIMATE;
+use datafusion_doc::DocSection;
 use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
 use datafusion_expr::utils::format_state_name;
 use datafusion_expr::{
     Accumulator, AggregateUDFImpl, Documentation, Signature, Volatility,
 };
+use datafusion_macros::user_doc;
 use std::any::Any;
 use std::fmt::{Debug, Formatter};
 use std::hash::Hash;
 use std::marker::PhantomData;
 use std::sync::OnceLock;
+
 make_udaf_expr_and_func!(
     ApproxDistinct,
     approx_distinct,
@@ -243,6 +245,20 @@ impl Default for ApproxDistinct {
     }
 }
 
+#[user_doc(
+    doc_section(label = "Approximate Functions"),
+    description = "Returns the approximate number of distinct input values calculated using the HyperLogLog algorithm.",
+    syntax_example = "approx_distinct(expression)",
+    sql_example = r#"```sql
+> SELECT approx_distinct(column_name) FROM table_name;
++-----------------------------------+
+| approx_distinct(column_name)      |
++-----------------------------------+
+| 42                                |
++-----------------------------------+
+```"#,
+    standard_argument(name = "expression",)
+)]
 pub struct ApproxDistinct {
     signature: Signature,
 }
@@ -309,25 +325,6 @@ impl AggregateUDFImpl for ApproxDistinct {
     }
 
     fn documentation(&self) -> Option<&Documentation> {
-        Some(get_approx_distinct_doc())
+        self.doc()
     }
 }
-
-static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
-
-fn get_approx_distinct_doc() -> &'static Documentation {
-    DOCUMENTATION.get_or_init(|| {
-        Documentation::builder(DOC_SECTION_APPROXIMATE, "Returns the approximate number of distinct input values calculated using the HyperLogLog algorithm.", "approx_distinct(expression)")
-            .with_sql_example(r#"```sql
-> SELECT approx_distinct(column_name) FROM table_name;
-+-----------------------------------+
-| approx_distinct(column_name)      |
-+-----------------------------------+
-| 42                                |
-+-----------------------------------+
-```"#, 
-            )
-            .with_standard_argument("expression", None)
-            .build()
-    })
-}

datafusion/functions-aggregate/src/approx_median.rs

@@ -25,13 +25,14 @@ use arrow::{datatypes::DataType, datatypes::Field};
 use arrow_schema::DataType::{Float64, UInt64};
 
 use datafusion_common::{not_impl_err, plan_err, Result};
-use datafusion_expr::aggregate_doc_sections::DOC_SECTION_APPROXIMATE;
+use datafusion_doc::DocSection;
 use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
 use datafusion_expr::type_coercion::aggregates::NUMERICS;
 use datafusion_expr::utils::format_state_name;
 use datafusion_expr::{
     Accumulator, AggregateUDFImpl, Documentation, Signature, Volatility,
 };
+use datafusion_macros::user_doc;
 
 use crate::approx_percentile_cont::ApproxPercentileAccumulator;
 
@@ -44,6 +45,20 @@ make_udaf_expr_and_func!(
 );
 
 /// APPROX_MEDIAN aggregate expression
+#[user_doc(
+    doc_section(label = "Approximate Functions"),
+    description = "Returns the approximate median (50th percentile) of input values. It is an alias of `approx_percentile_cont(x, 0.5)`.",
+    syntax_example = "approx_median(expression)",
+    sql_example = r#"```sql
+> SELECT approx_median(column_name) FROM table_name;
++-----------------------------------+
+| approx_median(column_name)        |
++-----------------------------------+
+| 23.5                              |
++-----------------------------------+
+```"#,
+    standard_argument(name = "expression",)
+)]
 pub struct ApproxMedian {
     signature: Signature,
 }
@@ -122,29 +137,6 @@ impl AggregateUDFImpl for ApproxMedian {
     }
 
     fn documentation(&self) -> Option<&Documentation> {
-        Some(get_approx_median_doc())
+        self.doc()
     }
 }
-
-static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
-
-fn get_approx_median_doc() -> &'static Documentation {
-    DOCUMENTATION.get_or_init(|| {
-        Documentation::builder(
-            DOC_SECTION_APPROXIMATE,
-                "Returns the approximate median (50th percentile) of input values. It is an alias of `approx_percentile_cont(x, 0.5)`.",
-
-            "approx_median(expression)")
-            .with_sql_example(r#"```sql
-> SELECT approx_median(column_name) FROM table_name;
-+-----------------------------------+
-| approx_median(column_name)        |
-+-----------------------------------+
-| 23.5                              |
-+-----------------------------------+
-```"#,
-            )
-            .with_standard_argument("expression", None)
-            .build()
-    })
-}

datafusion/functions-aggregate/src/approx_percentile_cont.rs

@@ -35,7 +35,7 @@ use datafusion_common::{
     downcast_value, internal_err, not_impl_datafusion_err, not_impl_err, plan_err,
     DataFusionError, Result, ScalarValue,
 };
-use datafusion_expr::aggregate_doc_sections::DOC_SECTION_APPROXIMATE;
+use datafusion_doc::DocSection;
 use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
 use datafusion_expr::type_coercion::aggregates::{INTEGERS, NUMERICS};
 use datafusion_expr::utils::format_state_name;
@@ -46,6 +46,7 @@ use datafusion_expr::{
 use datafusion_functions_aggregate_common::tdigest::{
     TDigest, TryIntoF64, DEFAULT_MAX_SIZE,
 };
+use datafusion_macros::user_doc;
 use datafusion_physical_expr_common::physical_expr::PhysicalExpr;
 
 create_func!(ApproxPercentileCont, approx_percentile_cont_udaf);
@@ -64,6 +65,28 @@ pub fn approx_percentile_cont(
     approx_percentile_cont_udaf().call(args)
 }
 
+#[user_doc(
+    doc_section(label = "Approximate Functions"),
+    description = "Returns the approximate percentile of input values using the t-digest algorithm.",
+    syntax_example = "approx_percentile_cont(expression, percentile, centroids)",
+    sql_example = r#"```sql
+> SELECT approx_percentile_cont(column_name, 0.75, 100) FROM table_name;
++-------------------------------------------------+
+| approx_percentile_cont(column_name, 0.75, 100)  |
++-------------------------------------------------+
+| 65.0                                            |
++-------------------------------------------------+
+```"#,
+    standard_argument(name = "expression",),
+    argument(
+        name = "percentile",
+        description = "Percentile to compute. Must be a float value between 0 and 1 (inclusive)."
+    ),
+    argument(
+        name = "centroids",
+        description = "Number of centroids to use in the t-digest algorithm. _Default is 100_. A higher number results in more accurate approximation but requires more memory."
+    )
+)]
 pub struct ApproxPercentileCont {
     signature: Signature,
 }
@@ -272,33 +295,10 @@ impl AggregateUDFImpl for ApproxPercentileCont {
     }
 
     fn documentation(&self) -> Option<&Documentation> {
-        Some(get_approx_percentile_cont_doc())
+        self.doc()
     }
 }
 
-static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
-
-fn get_approx_percentile_cont_doc() -> &'static Documentation {
-    DOCUMENTATION.get_or_init(|| {
-        Documentation::builder(
-            DOC_SECTION_APPROXIMATE,
-                "Returns the approximate percentile of input values using the t-digest algorithm.",
-            "approx_percentile_cont(expression, percentile, centroids)")
-            .with_sql_example(r#"```sql
-> SELECT approx_percentile_cont(column_name, 0.75, 100) FROM table_name;
-+-------------------------------------------------+
-| approx_percentile_cont(column_name, 0.75, 100)  |
-+-------------------------------------------------+
-| 65.0                                            |
-+-------------------------------------------------+
-```"#)
-            .with_standard_argument("expression", None)
-            .with_argument("percentile", "Percentile to compute. Must be a float value between 0 and 1 (inclusive).")
-            .with_argument("centroids", "Number of centroids to use in the t-digest algorithm. _Default is 100_. A higher number results in more accurate approximation but requires more memory.")
-            .build()
-    })
-}
-
 #[derive(Debug)]
 pub struct ApproxPercentileAccumulator {
     digest: TDigest,