Shape with holes (#770)

* Shape with holes.

* rustfmt.

3 files changed, 184 insertions, 6 deletions

diff --git a/candle-core/src/shape.rs b/candle-core/src/shape.rs
index 9617d1ac..b1f56817 100644
--- a/candle-core/src/shape.rs
+++ b/candle-core/src/shape.rs
@@ -482,3 +482,171 @@ mod tests {
         assert_eq!(shape.stride_contiguous(), [458 * 792, 458, 1]);
     }
 }
+
+pub trait ShapeWithOneHole {
+    fn into_shape(self, el_count: usize) -> Result<Shape>;
+}
+
+impl<S: Into<Shape>> ShapeWithOneHole for S {
+    fn into_shape(self, _el_count: usize) -> Result<Shape> {
+        Ok(self.into())
+    }
+}
+
+impl ShapeWithOneHole for ((),) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        Ok(el_count.into())
+    }
+}
+
+impl ShapeWithOneHole for ((), usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let ((), d1) = self;
+        if el_count % d1 != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d1}")
+        }
+        Ok((el_count / d1, d1).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, ()) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, ()) = self;
+        if el_count % d1 != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d1}")
+        }
+        Ok((d1, el_count / d1).into())
+    }
+}
+
+impl ShapeWithOneHole for ((), usize, usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let ((), d1, d2) = self;
+        let d = d1 * d2;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((el_count / d, d1, d2).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, (), usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, (), d2) = self;
+        let d = d1 * d2;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((d1, el_count / d, d2).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, usize, ()) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, d2, ()) = self;
+        let d = d1 * d2;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((d1, d2, el_count / d).into())
+    }
+}
+
+impl ShapeWithOneHole for ((), usize, usize, usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let ((), d1, d2, d3) = self;
+        let d = d1 * d2 * d3;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((el_count / d, d1, d2, d3).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, (), usize, usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, (), d2, d3) = self;
+        let d = d1 * d2 * d3;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((d1, el_count / d, d2, d3).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, usize, (), usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, d2, (), d3) = self;
+        let d = d1 * d2 * d3;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((d1, d2, el_count / d, d3).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, usize, usize, ()) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, d2, d3, ()) = self;
+        let d = d1 * d2 * d3;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((d1, d2, d3, el_count / d).into())
+    }
+}
+
+impl ShapeWithOneHole for ((), usize, usize, usize, usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let ((), d1, d2, d3, d4) = self;
+        let d = d1 * d2 * d3 * d4;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((el_count / d, d1, d2, d3, d4).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, (), usize, usize, usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, (), d2, d3, d4) = self;
+        let d = d1 * d2 * d3 * d4;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((d1, el_count / d, d2, d3, d4).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, usize, (), usize, usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, d2, (), d3, d4) = self;
+        let d = d1 * d2 * d3 * d4;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((d1, d2, el_count / d, d3, d4).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, usize, usize, (), usize) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, d2, d3, (), d4) = self;
+        let d = d1 * d2 * d3 * d4;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((d1, d2, d3, el_count / d, d4).into())
+    }
+}
+
+impl ShapeWithOneHole for (usize, usize, usize, usize, ()) {
+    fn into_shape(self, el_count: usize) -> Result<Shape> {
+        let (d1, d2, d3, d4, ()) = self;
+        let d = d1 * d2 * d3 * d4;
+        if el_count % d != 0 {
+            crate::bail!("tensor number of elements {el_count} is not divisible by {d}")
+        }
+        Ok((d1, d2, d3, d4, el_count / d).into())
+    }
+}
diff --git a/candle-core/src/tensor.rs b/candle-core/src/tensor.rs
index 1eca694c..6bb3d740 100644
--- a/candle-core/src/tensor.rs
+++ b/candle-core/src/tensor.rs
@@ -1685,12 +1685,15 @@ impl Tensor {
         Ok(from_storage(storage, shape, BackpropOp::none(), true))
     }
 
-    // TODO: Do we want to allow target shape using -1 on some dimensions?
     /// Reshape returns a tensor with the target shape provided that the number of elements of the
     /// original tensor is the same.
     /// If the input tensor is contiguous, this is a view on the original data. Otherwise this uses
     /// a new storage and copies the data over, the returned tensor is always contiguous.
     ///
+    /// The shape can be specified using a tuple of `usize` and at most one `()` in which case
+    /// the behavior is the same as when using `-1` in PyTorch: this dimension size is adjusted so
+    /// as to match the number of elements in the tensor.
+    ///
     /// ```rust
     /// # use candle_core::{Tensor, DType, Device, D};
     /// let a = Tensor::zeros((2, 3), DType::F32, &Device::Cpu)?;
@@ -1700,10 +1703,14 @@ impl Tensor {
     ///
     /// let c = a.reshape((3, 2))?;
     /// assert_eq!(c.shape().dims(), &[3, 2]);
+    ///
+    /// let c = a.reshape((2, (), 1))?;
+    /// assert_eq!(c.shape().dims(), &[2, 3, 1]);
+    ///
     /// # Ok::<(), candle_core::Error>(())
     /// ```
-    pub fn reshape<S: Into<Shape>>(&self, shape: S) -> Result<Tensor> {
-        let shape = shape.into();
+    pub fn reshape<S: crate::shape::ShapeWithOneHole>(&self, s: S) -> Result<Tensor> {
+        let shape = s.into_shape(self.elem_count())?;
         if shape.elem_count() != self.elem_count() {
             return Err(Error::ShapeMismatchBinaryOp {
                 lhs: self.shape().clone(),
diff --git a/candle-flash-attn/build.rs b/candle-flash-attn/build.rs
index 4cc7e5fb..64275fda 100644
--- a/candle-flash-attn/build.rs
+++ b/candle-flash-attn/build.rs
@@ -57,10 +57,13 @@ fn main() -> Result<()> {
             #[allow(clippy::redundant_clone)]
             out_dir.clone()
         }
-        Ok(build_dir) =>
-        {
+        Ok(build_dir) => {
             let path = PathBuf::from(build_dir);
-            path.canonicalize().expect(&format!("Directory doesn't exists: {} (the current directory is {})", &path.display(), std::env::current_dir()?.display()))
+            path.canonicalize().expect(&format!(
+                "Directory doesn't exists: {} (the current directory is {})",
+                &path.display(),
+                std::env::current_dir()?.display()
+            ))
         }
     };
     set_cuda_include_dir()?;