Migrate documentation for all string functions from scalar_functions…

….md to code (#12775)

* Added documentation for string and unicode functions.

* Fixed issues with aliases.

* Cargo fmt.

* Minor doc fixes.

* Update docs for var_pop/samp

---------

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

datafusion/core/src/bin/print_functions_docs.rs

@@ -130,13 +130,14 @@ fn print_docs(
                 .find(|f| f.get_name() == name || f.get_aliases().contains(&name))
                 .unwrap();
 
-            let name = f.get_name();
             let aliases = f.get_aliases();
             let documentation = f.get_documentation();
 
             // if this name is an alias we need to display what it's an alias of
             if aliases.contains(&name) {
-                let _ = write!(docs, "_Alias of [{name}](#{name})._");
+                let fname = f.get_name();
+                let _ = writeln!(docs, r#"### `{name}`"#);
+                let _ = writeln!(docs, "_Alias of [{fname}](#{fname})._");
                 continue;
             }
 
@@ -183,10 +184,10 @@ fn print_docs(
 
             // next, aliases
             if !f.get_aliases().is_empty() {
-                let _ = write!(docs, "#### Aliases");
+                let _ = writeln!(docs, "#### Aliases");
 
                 for alias in f.get_aliases() {
-                    let _ = writeln!(docs, "- {alias}");
+                    let _ = writeln!(docs, "- {}", alias.replace("_", r#"\_"#));
                 }
             }
 

datafusion/functions/src/string/ascii.rs

@@ -26,24 +26,6 @@ use datafusion_expr::{ScalarUDFImpl, Signature, Volatility};
 use std::any::Any;
 use std::sync::{Arc, OnceLock};
 
-static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
-
-fn get_ascii_doc() -> &'static Documentation {
-    DOCUMENTATION.get_or_init(|| {
-        Documentation::builder()
-            .with_doc_section(DOC_SECTION_STRING)
-            .with_description("Returns the ASCII value of the first character in a string.")
-            .with_syntax_example("ascii(str)")
-            .with_argument(
-                "str",
-                "String expression to operate on. Can be a constant, column, or function that evaluates to or can be coerced to a Utf8, LargeUtf8 or a Utf8View.",
-            )
-            .with_related_udf("chr")
-            .build()
-            .unwrap()
-    })
-}
-
 #[derive(Debug)]
 pub struct AsciiFunc {
     signature: Signature,
@@ -96,6 +78,39 @@ impl ScalarUDFImpl for AsciiFunc {
     }
 }
 
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_ascii_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_STRING)
+            .with_description(
+                "Returns the Unicode character code of the first character in a string.",
+            )
+            .with_syntax_example("ascii(str)")
+            .with_sql_example(
+                r#"```sql
+> select ascii('abc');
++--------------------+
+| ascii(Utf8("abc")) |
++--------------------+
+| 97                 |
++--------------------+
+> select ascii('🚀');
++-------------------+
+| ascii(Utf8("🚀")) |
++-------------------+
+| 128640            |
++-------------------+
+```"#,
+            )
+            .with_standard_argument("str", "String")
+            .with_related_udf("chr")
+            .build()
+            .unwrap()
+    })
+}
+
 fn calculate_ascii<'a, V>(array: V) -> Result<ArrayRef, ArrowError>
 where
     V: ArrayAccessor<Item = &'a str>,

datafusion/functions/src/string/bit_length.rs

@@ -15,17 +15,17 @@
 // specific language governing permissions and limitations
 // under the License.
 
-use std::any::Any;
-
 use arrow::compute::kernels::length::bit_length;
 use arrow::datatypes::DataType;
+use std::any::Any;
+use std::sync::OnceLock;
 
+use crate::utils::utf8_to_int_type;
 use datafusion_common::{exec_err, Result, ScalarValue};
-use datafusion_expr::{ColumnarValue, Volatility};
+use datafusion_expr::scalar_doc_sections::DOC_SECTION_STRING;
+use datafusion_expr::{ColumnarValue, Documentation, Volatility};
 use datafusion_expr::{ScalarUDFImpl, Signature};
 
-use crate::utils::utf8_to_int_type;
-
 #[derive(Debug)]
 pub struct BitLengthFunc {
     signature: Signature,
@@ -88,4 +88,34 @@ impl ScalarUDFImpl for BitLengthFunc {
             },
         }
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_bit_length_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_bit_length_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_STRING)
+            .with_description("Returns the bit length of a string.")
+            .with_syntax_example("bit_length(str)")
+            .with_sql_example(
+                r#"```sql
+> select bit_length('datafusion');
++--------------------------------+
+| bit_length(Utf8("datafusion")) |
++--------------------------------+
+| 80                             |
++--------------------------------+
+```"#,
+            )
+            .with_standard_argument("str", "String")
+            .with_related_udf("length")
+            .with_related_udf("octet_length")
+            .build()
+            .unwrap()
+    })
 }

datafusion/functions/src/string/btrim.rs

@@ -15,18 +15,18 @@
 // specific language governing permissions and limitations
 // under the License.
 
+use crate::string::common::*;
+use crate::utils::{make_scalar_function, utf8_to_str_type};
 use arrow::array::{ArrayRef, OffsetSizeTrait};
 use arrow::datatypes::DataType;
-use std::any::Any;
-
 use datafusion_common::{exec_err, Result};
 use datafusion_expr::function::Hint;
+use datafusion_expr::scalar_doc_sections::DOC_SECTION_STRING;
 use datafusion_expr::TypeSignature::*;
-use datafusion_expr::{ColumnarValue, Volatility};
+use datafusion_expr::{ColumnarValue, Documentation, Volatility};
 use datafusion_expr::{ScalarUDFImpl, Signature};
-
-use crate::string::common::*;
-use crate::utils::{make_scalar_function, utf8_to_str_type};
+use std::any::Any;
+use std::sync::OnceLock;
 
 /// Returns the longest string with leading and trailing characters removed. If the characters are not specified, whitespace is removed.
 /// btrim('xyxtrimyyx', 'xyz') = 'trim'
@@ -109,6 +109,35 @@ impl ScalarUDFImpl for BTrimFunc {
     fn aliases(&self) -> &[String] {
         &self.aliases
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_btrim_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_btrim_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_STRING)
+            .with_description("Trims the specified trim string from the start and end of a string. If no trim string is provided, all whitespace is removed from the start and end of the input string.")
+            .with_syntax_example("btrim(str[, trim_str])")
+            .with_sql_example(r#"```sql
+> select btrim('__datafusion____', '_');
++-------------------------------------------+
+| btrim(Utf8("__datafusion____"),Utf8("_")) |
++-------------------------------------------+
+| datafusion                                |
++-------------------------------------------+
+```"#)
+            .with_standard_argument("str", "String")
+            .with_argument("trim_str", "String expression to operate on. Can be a constant, column, or function, and any combination of operators. _Default is whitespace characters._")
+            .with_related_udf("ltrim")
+            .with_related_udf("rtrim")
+            .build()
+            .unwrap()
+    })
 }
 
 #[cfg(test)]

datafusion/functions/src/string/chr.rs

@@ -16,21 +16,21 @@
 // under the License.
 
 use std::any::Any;
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
 
 use arrow::array::ArrayRef;
 use arrow::array::StringArray;
 use arrow::datatypes::DataType;
 use arrow::datatypes::DataType::Int64;
 use arrow::datatypes::DataType::Utf8;
 
+use crate::utils::make_scalar_function;
 use datafusion_common::cast::as_int64_array;
 use datafusion_common::{exec_err, Result};
-use datafusion_expr::{ColumnarValue, Volatility};
+use datafusion_expr::scalar_doc_sections::DOC_SECTION_STRING;
+use datafusion_expr::{ColumnarValue, Documentation, Volatility};
 use datafusion_expr::{ScalarUDFImpl, Signature};
 
-use crate::utils::make_scalar_function;
-
 /// Returns the character with the given code. chr(0) is disallowed because text data types cannot store that character.
 /// chr(65) = 'A'
 pub fn chr(args: &[ArrayRef]) -> Result<ArrayRef> {
@@ -99,4 +99,35 @@ impl ScalarUDFImpl for ChrFunc {
     fn invoke(&self, args: &[ColumnarValue]) -> Result<ColumnarValue> {
         make_scalar_function(chr, vec![])(args)
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_chr_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_chr_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_STRING)
+            .with_description(
+                "Returns the character with the specified ASCII or Unicode code value.",
+            )
+            .with_syntax_example("chr(expression)")
+            .with_sql_example(
+                r#"```sql
+> select chr(128640);
++--------------------+
+| chr(Int64(128640)) |
++--------------------+
+| 🚀                 |
++--------------------+ 
+```"#,
+            )
+            .with_standard_argument("expression", "String")
+            .with_related_udf("ascii")
+            .build()
+            .unwrap()
+    })
 }

datafusion/functions/src/string/concat.rs

@@ -18,18 +18,18 @@
 use arrow::array::{as_largestring_array, Array};
 use arrow::datatypes::DataType;
 use std::any::Any;
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
 
+use crate::string::common::*;
+use crate::string::concat;
 use datafusion_common::cast::{as_string_array, as_string_view_array};
 use datafusion_common::{internal_err, plan_err, Result, ScalarValue};
 use datafusion_expr::expr::ScalarFunction;
+use datafusion_expr::scalar_doc_sections::DOC_SECTION_STRING;
 use datafusion_expr::simplify::{ExprSimplifyResult, SimplifyInfo};
-use datafusion_expr::{lit, ColumnarValue, Expr, Volatility};
+use datafusion_expr::{lit, ColumnarValue, Documentation, Expr, Volatility};
 use datafusion_expr::{ScalarUDFImpl, Signature};
 
-use crate::string::common::*;
-use crate::string::concat;
-
 #[derive(Debug)]
 pub struct ConcatFunc {
     signature: Signature,
@@ -244,6 +244,36 @@ impl ScalarUDFImpl for ConcatFunc {
     ) -> Result<ExprSimplifyResult> {
         simplify_concat(args)
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_concat_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_concat_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_STRING)
+            .with_description("Concatenates multiple strings together.")
+            .with_syntax_example("concat(str[, ..., str_n])")
+            .with_sql_example(
+                r#"```sql
+> select concat('data', 'f', 'us', 'ion');
++-------------------------------------------------------+
+| concat(Utf8("data"),Utf8("f"),Utf8("us"),Utf8("ion")) |
++-------------------------------------------------------+
+| datafusion                                            |
++-------------------------------------------------------+
+```"#,
+            )
+            .with_standard_argument("str", "String")
+            .with_argument("str_n", "Subsequent string expressions to concatenate.")
+            .with_related_udf("concat_ws")
+            .build()
+            .unwrap()
+    })
 }
 
 pub fn simplify_concat(args: Vec<Expr>) -> Result<ExprSimplifyResult> {