From 43655b8a0c62d9bceda235a2001bd3e239d81f25 Mon Sep 17 00:00:00 2001
From: Eduard Urbach <eduard@urbach.dev>
Date: Sat, 23 Aug 2025 20:23:57 +0200
Subject: [PATCH] Added an error message for missing function implementations

---
 src/core/errors.go                     |  9 +++++++++
 src/core/errors_test.go                |  1 +
 src/core/evaluateDot.go                |  4 ++++
 src/core/evaluateToken.go              | 11 +++++++++--
 src/core/testdata/NoMatchingFunction.q |  6 ++++++
 5 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 src/core/testdata/NoMatchingFunction.q

diff --git a/src/core/errors.go b/src/core/errors.go
index 3d22f0b..847f19c 100644
--- a/src/core/errors.go
+++ b/src/core/errors.go
@@ -34,6 +34,15 @@ func (err *DefinitionCountMismatch) Error() string {
 	return fmt.Sprintf("Not enough variables for the return value of '%s'", err.Function)
 }
 
+// NoMatchingFunction is created when a function is not defined for the given type.
+type NoMatchingFunction struct {
+	Function string
+}
+
+func (err *NoMatchingFunction) Error() string {
+	return fmt.Sprintf("No matching function for call to '%s'", err.Function)
+}
+
 // ParameterCountMismatch error is created when the number of provided parameters doesn't match the function signature.
 type ParameterCountMismatch struct {
 	Function      string
diff --git a/src/core/errors_test.go b/src/core/errors_test.go
index a4c6dc7..1220a76 100644
--- a/src/core/errors_test.go
+++ b/src/core/errors_test.go
@@ -29,6 +29,7 @@ var errs = []struct {
 	{"InvalidStructOperation.q", core.InvalidStructOperation},
 	{"InvalidStructOperation2.q", core.InvalidStructOperation},
 	{"MissingOperand.q", core.MissingOperand},
+	{"NoMatchingFunction.q", &core.NoMatchingFunction{Function: "main.f"}},
 	{"ParameterCountMismatch.q", &core.ParameterCountMismatch{Function: "main.f", Count: 0, ExpectedCount: 1}},
 	{"ParameterCountMismatch2.q", &core.ParameterCountMismatch{Function: "main.f", Count: 2, ExpectedCount: 1}},
 	{"ReturnCountMismatch.q", &core.ReturnCountMismatch{Count: 1, ExpectedCount: 0}},
diff --git a/src/core/evaluateDot.go b/src/core/evaluateDot.go
index d424730..32c25c8 100644
--- a/src/core/evaluateDot.go
+++ b/src/core/evaluateDot.go
@@ -48,6 +48,10 @@ func (f *Function) evaluateDot(expr *expression.Expression) (ssa.Value, error) {
 			return nil, err
 		}
 
+		if fn == nil {
+			return nil, errors.New(&NoMatchingFunction{Function: fmt.Sprintf("%s.%s", pkg.Name, rightText)}, f.File, left.Token.Position)
+		}
+
 		if fn.IsExtern() {
 			f.Assembler.Libraries.Append(fn.Package, fn.Name)
 		} else {
diff --git a/src/core/evaluateToken.go b/src/core/evaluateToken.go
index b5a5f69..cfe679d 100644
--- a/src/core/evaluateToken.go
+++ b/src/core/evaluateToken.go
@@ -1,6 +1,8 @@
 package core
 
 import (
+	"fmt"
+
 	"git.urbach.dev/cli/q/src/errors"
 	"git.urbach.dev/cli/q/src/expression"
 	"git.urbach.dev/cli/q/src/ssa"
@@ -62,7 +64,12 @@ func (f *Function) evaluateLeaf(expr *expression.Expression) (ssa.Value, error)
 		}
 
 		pkg := f.Env.Packages[f.File.Package]
-		variants := pkg.Functions[name]
+		variants, exists := pkg.Functions[name]
+
+		if !exists {
+			return nil, errors.New(&UnknownIdentifier{Name: name}, f.File, expr.Token.Position)
+		}
+
 		inputExpressions := expr.Parent.Children[1:]
 		fn, err := f.selectFunction(variants, inputExpressions, expr)
 
@@ -84,7 +91,7 @@ func (f *Function) evaluateLeaf(expr *expression.Expression) (ssa.Value, error)
 			return v, nil
 		}
 
-		return nil, errors.New(&UnknownIdentifier{Name: name}, f.File, expr.Token.Position)
+		return nil, errors.New(&NoMatchingFunction{Function: fmt.Sprintf("%s.%s", pkg.Name, name)}, f.File, expr.Token.Position)
 
 	case token.Number, token.Rune:
 		number, err := toNumber(expr.Token, f.File)
diff --git a/src/core/testdata/NoMatchingFunction.q b/src/core/testdata/NoMatchingFunction.q
new file mode 100644
index 0000000..c031e15
--- /dev/null
+++ b/src/core/testdata/NoMatchingFunction.q
@@ -0,0 +1,6 @@
+main() {
+	f()
+}
+
+f(_ string) {}
+f(_ int) {}
\ No newline at end of file
-- 
2.51.2