compile/compile: Fix panic from CLI + metadata entrypoint overlaps.

This commit fixes a panic that could occur when `opa build` was provided
an entrypoint from both a CLI flag, and via entrypoint metadata
annotation.

The fix is simple: deduplicate the slice of entrypoint refs that the
compiler uses, before compiling WASM or Plan targets.

Fixes: open-policy-agent#6661

Signed-off-by: Philip Conrad <philipaconrad@gmail.com>

compile/compile.go

@@ -326,6 +326,12 @@ func (c *Compiler) Build(ctx context.Context) error {
 		return err
 	}
 
+	// Dedup entrypoint refs, if both CLI and entrypoint metadata annotations
+	// were used.
+	if err := c.dedupEntrypointRefs(); err != nil {
+		return err
+	}
+
 	if err := c.optimize(ctx); err != nil {
 		return err
 	}
@@ -429,6 +435,30 @@ func (c *Compiler) checkNumEntrypoints() error {
 	return nil
 }
 
+// Note(philipc): When an entrypoint is provided on the CLI and from an
+// entrypoint annotation, it can lead to duplicates in the slice of
+// entrypoint refs. This can cause panics down the line due to c.entrypoints
+// being a different length than c.entrypointrefs. As a result, we have to
+// trim out the duplicates.
+func (c *Compiler) dedupEntrypointRefs() error {
+	// Discover the distinct entrypoint refs.
+	entrypointRefSet := make(map[string]int, len(c.entrypointrefs))
+	for i, r := range c.entrypointrefs {
+		refString := r.String()
+		// Store only the first index in the list that matches.
+		if _, ok := entrypointRefSet[refString]; !ok {
+			entrypointRefSet[refString] = i
+		}
+	}
+	// Build list of entrypoint refs, without duplicates.
+	newEntrypointRefs := make([]*ast.Term, 0, len(entrypointRefSet))
+	for _, idx := range entrypointRefSet {
+		newEntrypointRefs = append(newEntrypointRefs, c.entrypointrefs[idx])
+	}
+	c.entrypointrefs = newEntrypointRefs
+	return nil
+}
+
 // Bundle returns the compiled bundle. This function can be called to retrieve the
 // output of the compiler (as an alternative to having the bundle written to a stream.)
 func (c *Compiler) Bundle() *bundle.Bundle {

compile/compile_test.go

@@ -978,9 +978,7 @@ update {
 
 func modulesToString(modules []bundle.ModuleFile) string {
 	var buf bytes.Buffer
-	//result := make([]string, len(modules))
 	for i, m := range modules {
-		//result[i] = m.Parsed.String()
 		buf.WriteString(strconv.Itoa(i))
 		buf.WriteString(":\n")
 		buf.WriteString(string(m.Raw))
@@ -1623,6 +1621,28 @@ q[3]
 				"test/p":      {},
 			},
 		},
+		{
+			note:        "overlapping manual entrypoints + annotation entrypoints",
+			entrypoints: []string{"test/p"},
+			modules: map[string]string{
+				"test.rego": `
+package test
+
+# METADATA
+# entrypoint: true
+p {
+	q[input.x]
+}
+
+q[1]
+q[2]
+q[3]
+				`,
+			},
+			wantEntrypoints: map[string]struct{}{
+				"test/p": {},
+			},
+		},
 		{
 			note:        "ref head rule annotation",
 			entrypoints: []string{},