feat: implement getStaticPaths hoisting (#137)

.changeset/forty-crews-greet.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/compiler': patch
+---
+
+Implement getStaticPaths hoisting

internal/js_scanner/js_scanner.go

@@ -137,6 +137,130 @@ func HasExports(source []byte) bool {
 	}
 }
 
+type HoistedScripts struct {
+	Hoisted [][]byte
+	Body    []byte
+}
+
+func HoistExports(source []byte) HoistedScripts {
+	shouldHoist := hasGetStaticPaths(source)
+	if !shouldHoist {
+		return HoistedScripts{
+			Body: source,
+		}
+	}
+
+	l := js.NewLexer(parse.NewInputBytes(source))
+	i := 0
+	pairs := make(map[byte]int)
+
+	// Let's lex the script until we find what we need!
+	for {
+		token, value := l.Next()
+
+		if token == js.ErrorToken {
+			if l.Err() != io.EOF {
+				return HoistedScripts{
+					Body: source,
+				}
+			}
+			break
+		}
+
+		// Common delimeters. Track their length, then skip.
+		if token == js.WhitespaceToken || token == js.LineTerminatorToken || token == js.SemicolonToken {
+			i += len(value)
+			continue
+		}
+
+		// Exports should be consumed until all opening braces are closed,
+		// a specifier is found, and a line terminator has been found
+		if token == js.ExportToken {
+			foundGetStaticPaths := false
+			foundSemicolonOrLineTerminator := false
+			start := i - 1
+			i += len(value)
+			for {
+				next, nextValue := l.Next()
+				i += len(nextValue)
+
+				if js.IsIdentifier(next) {
+					if !foundGetStaticPaths {
+						foundGetStaticPaths = string(nextValue) == "getStaticPaths"
+					}
+				} else if next == js.LineTerminatorToken || next == js.SemicolonToken {
+					foundSemicolonOrLineTerminator = true
+				} else if js.IsPunctuator(next) {
+					if nextValue[0] == '{' || nextValue[0] == '(' || nextValue[0] == '[' {
+						pairs[nextValue[0]]++
+					} else if nextValue[0] == '}' {
+						pairs['{']--
+					} else if nextValue[0] == ')' {
+						pairs['(']--
+					} else if nextValue[0] == ']' {
+						pairs['[']--
+					}
+				}
+
+				if next == js.ErrorToken {
+					return HoistedScripts{
+						Body: source,
+					}
+				}
+
+				if foundGetStaticPaths && foundSemicolonOrLineTerminator && pairs['{'] == 0 && pairs['('] == 0 && pairs['['] == 0 {
+					hoisted := make([][]byte, 1)
+					hoisted = append(hoisted, source[start:i])
+					body := make([]byte, 0)
+					body = append(body, source[0:start]...)
+					body = append(body, source[i:]...)
+					return HoistedScripts{
+						Hoisted: hoisted,
+						Body:    body,
+					}
+				}
+			}
+		}
+
+		// Track opening and closing braces
+		if js.IsPunctuator(token) {
+			if value[0] == '{' || value[0] == '(' || value[0] == '[' {
+				pairs[value[0]]++
+				i += len(value)
+				continue
+			} else if value[0] == '}' {
+				pairs['{']--
+			} else if value[0] == ')' {
+				pairs['(']--
+			} else if value[0] == ']' {
+				pairs['[']--
+			}
+		}
+
+		// Track our current position
+		i += len(value)
+	}
+
+	// If we haven't found anything... there's nothing to find! Split at the start.
+	return HoistedScripts{
+		Body: source,
+	}
+}
+
+func hasGetStaticPaths(source []byte) bool {
+	l := js.NewLexer(parse.NewInputBytes(source))
+	for {
+		token, value := l.Next()
+		if token == js.ErrorToken {
+			// EOF or other error
+			return false
+		}
+		if token == js.IdentifierToken && string(value) == "getStaticPaths" {
+			return true
+		}
+	}
+}
+
 func AccessesPrivateVars(source []byte) bool {
 	l := js.NewLexer(parse.NewInputBytes(source))
 	for {

internal/printer/print-to-js.go

@@ -5,7 +5,6 @@
 package printer
 
 import (
-	"errors"
 	"fmt"
 	"sort"
 	"strings"
@@ -117,13 +116,17 @@ func render1(p *printer, n *Node, opts RenderOptions) {
 				p.addSourceMapping(n.Loc[0])
 				if renderBodyStart == -1 {
 					p.addSourceMapping(c.Loc[0])
-					if js_scanner.AccessesPrivateVars([]byte(c.Data)) {
-						panic(errors.New("Variables prefixed by \"$$\" are reserved for Astro's internal usage!"))
-					}
+					preprocessed := js_scanner.HoistExports([]byte(c.Data))
 
 					// 1. After imports put in the top-level Astro.
 					p.printTopLevelAstro()
 
+					if len(preprocessed.Hoisted) > 0 {
+						for _, hoisted := range preprocessed.Hoisted {
+							p.println(strings.TrimSpace(string(hoisted)))
+						}
+					}
+
 					// 2. The frontmatter.
 					p.print(strings.TrimSpace(c.Data))
 
@@ -134,14 +137,9 @@ func render1(p *printer, n *Node, opts RenderOptions) {
 					p.printFuncPrelude("$$Component")
 				} else {
 					importStatements := c.Data[0:renderBodyStart]
-					renderBody := c.Data[renderBodyStart:]
+					content := c.Data[renderBodyStart:]
+					preprocessed := js_scanner.HoistExports([]byte(content))
 
-					if js_scanner.HasExports([]byte(renderBody)) {
-						panic(errors.New("Export statements must be placed at the top of .astro files!"))
-					}
-					//  {
-					// 	panic(errors.New("Variables prefixed by \"$$\" are reserved for Astro's internal usage!"))
-					// }
 					p.addSourceMapping(c.Loc[0])
 					p.println(strings.TrimSpace(importStatements))
 
@@ -150,10 +148,16 @@ func render1(p *printer, n *Node, opts RenderOptions) {
 					// 2. Top-level Astro global.
 					p.printTopLevelAstro()
 
+					if len(preprocessed.Hoisted) > 0 {
+						for _, hoisted := range preprocessed.Hoisted {
+							p.println(strings.TrimSpace(string(hoisted)))
+						}
+					}
+
 					// TODO: use the proper component name
 					p.printFuncPrelude("$$Component")
 					p.addSourceMapping(loc.Loc{Start: c.Loc[0].Start + renderBodyStart})
-					p.print(strings.TrimSpace(renderBody))
+					p.print(strings.TrimSpace(string(preprocessed.Body)))
 				}
 
 				// Print empty just to ensure a newline

internal/printer/printer_test.go

@@ -41,9 +41,10 @@ var CREATE_ASTRO_CALL = "const $$Astro = $$createAstro(import.meta.url, 'https:/
 var NON_WHITESPACE_CHARS = []byte("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^&*()-_=+[];:'\",.?")
 
 type want struct {
-	frontmatter []string
-	styles      []string
-	scripts     []string
+	frontmatter    []string
+	styles         []string
+	scripts        []string
+	getStaticPaths string
 	metadata
 	code string
 }
@@ -86,6 +87,57 @@ const href = '/about';
 				code:        `<html><head></head><body><a${` + ADD_ATTRIBUTE + `(href, "href")}>About</a></body></html>`,
 			},
 		},
+		{
+			name: "getStaticPaths (basic)",
+			source: `---
+export const getStaticPaths = async () => {
+	return { paths: [] }
+}
+---
+<div></div>`,
+			want: want{
+				frontmatter: []string{`export const getStaticPaths = async () => {
+	return { paths: [] }
+}`, ""},
+				code: `<html><head></head><body><div></div></body></html>`,
+			},
+		},
+		{
+			name: "getStaticPaths (hoisted)",
+			source: `---
+const a = 0;
+export const getStaticPaths = async () => {
+	return { paths: [] }
+}
+---
+<div></div>`,
+			want: want{
+				frontmatter: []string{"", `const a = 0;`},
+				getStaticPaths: `export const getStaticPaths = async () => {
+	return { paths: [] }
+}`,
+				code: `<html><head></head><body><div></div></body></html>`,
+			},
+		},
+		{
+			name: "getStaticPaths (hoisted II)",
+			source: `---
+const a = 0;
+export async function getStaticPaths() {
+	return { paths: [] }
+}
+const b = 0;
+---
+<div></div>`,
+			want: want{
+				frontmatter: []string{"", `const a = 0;
+const b = 0;`},
+				getStaticPaths: `export async function getStaticPaths() {
+	return { paths: [] }
+}`,
+				code: `<html><head></head><body><div></div></body></html>`,
+			},
+		},
 		{
 			name: "component",
 			source: `---
@@ -1076,8 +1128,12 @@ import * as $$module1 from 'react-bootstrap';`},
 				}
 			}
 			metadata += "] }"
+
 			toMatch += "\n\n" + fmt.Sprintf("export const %s = %s(import.meta.url, %s);\n\n", METADATA, CREATE_METADATA, metadata)
 			toMatch += test_utils.Dedent(CREATE_ASTRO_CALL) + "\n\n"
+			if len(tt.want.getStaticPaths) > 0 {
+				toMatch += strings.TrimSpace(test_utils.Dedent(tt.want.getStaticPaths)) + "\n\n"
+			}
 			toMatch += test_utils.Dedent(PRELUDE) + "\n"
 			if len(tt.want.frontmatter) > 1 {
 				toMatch += test_utils.Dedent(tt.want.frontmatter[1])