[otelcol] Add hint about confmap.strictlyTypedInput feature gate (#10553)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

<!-- Issue number if applicable -->

Adds coda to errors related to `confmap.strictlyTypedInput` that direct
users to #10552 and explain the feature gate.

#### Link to tracking issue

Updates #9532

<!--Describe what testing was performed and which tests were added.-->
#### Testing

Tests that the coda is present when there are weakly typed errors and
not present with non weakly-typed errors.

<!--Describe the documentation added.-->

Author: mx-psi

.chloggen/mx-psi_clearer-error-message.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confmap
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add explanation to errors related to `confmap.strictlyTypedInput` feature gate.
+
+# One or more tracking issues or pull requests related to the change
+issues: [9532]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

otelcol/configprovider.go

@@ -6,8 +6,16 @@ package otelcol // import "go.opentelemetry.io/collector/otelcol"
 import (
 	"context"
 	"fmt"
+	"strings"
 
 	"go.opentelemetry.io/collector/confmap"
+	"go.opentelemetry.io/collector/internal/featuregates"
+)
+
+var (
+	strictlyTypedMessageCoda = `Hint: Temporarily restore the previous behavior by disabling 
+      the ` + fmt.Sprintf("`%s`", featuregates.StrictlyTypedInputID) + ` feature gate. More details at:
+      https://github.com/open-telemetry/opentelemetry-collector/issues/10552`
 )
 
 // ConfigProvider provides the service configuration.
@@ -95,7 +103,26 @@ func (cm *configProvider) Get(ctx context.Context, factories Factories) (*Config
 
 	var cfg *configSettings
 	if cfg, err = unmarshal(conf, factories); err != nil {
-		return nil, fmt.Errorf("cannot unmarshal the configuration: %w", err)
+		err = fmt.Errorf("cannot unmarshal the configuration: %w", err)
+
+		if featuregates.StrictlyTypedInputGate.IsEnabled() {
+			var shouldAddCoda bool
+			for _, errorStr := range []string{
+				"got unconvertible type",      // https://github.com/mitchellh/mapstructure/blob/8508981/mapstructure.go#L610
+				"source data must be",         // https://github.com/mitchellh/mapstructure/blob/8508981/mapstructure.go#L1114
+				"expected a map, got 'slice'", // https://github.com/mitchellh/mapstructure/blob/8508981/mapstructure.go#L831
+			} {
+				shouldAddCoda = strings.Contains(err.Error(), errorStr)
+				if shouldAddCoda {
+					break
+				}
+			}
+			if shouldAddCoda {
+				err = fmt.Errorf("%w\n\n%s", err, strictlyTypedMessageCoda)
+			}
+		}
+
+		return nil, err
 	}
 
 	return &Config{

otelcol/configprovider_test.go

@@ -14,6 +14,8 @@ import (
 	"gopkg.in/yaml.v3"
 
 	"go.opentelemetry.io/collector/confmap"
+	"go.opentelemetry.io/collector/featuregate"
+	"go.opentelemetry.io/collector/internal/featuregates"
 )
 
 func newConfig(yamlBytes []byte, factories Factories) (*Config, error) {
@@ -137,3 +139,75 @@ func TestGetConfmap(t *testing.T) {
 
 	assert.EqualValues(t, yamlMap, cmap.ToStringMap())
 }
+
+func TestStrictlyTypedCoda(t *testing.T) {
+	tests := []struct {
+		basename string
+		// isErrFromStrictTypes indicates whether the test should expect an error when the feature gate is
+		// disabled. If so, we check that it errs both with and without the feature gate and that the coda is never
+		// present.
+		isErrFromStrictTypes bool
+	}{
+		{basename: "weak-implicit-bool-to-string.yaml"},
+		{basename: "weak-implicit-int-to-string.yaml"},
+		{basename: "weak-implicit-bool-to-int.yaml"},
+		{basename: "weak-implicit-string-to-int.yaml"},
+		{basename: "weak-implicit-int-to-bool.yaml"},
+		{basename: "weak-implicit-string-to-bool.yaml"},
+		{basename: "weak-empty-map-to-empty-array.yaml"},
+		{basename: "weak-slice-of-maps-to-map.yaml"},
+		{basename: "weak-single-element-to-slice.yaml"},
+		{
+			basename:             "otelcol-invalid-components.yaml",
+			isErrFromStrictTypes: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.basename, func(t *testing.T) {
+			filename := filepath.Join("testdata", tt.basename)
+			uriLocation := "file:" + filename
+			fileProvider := newFakeProvider("file", func(_ context.Context, _ string, _ confmap.WatcherFunc) (*confmap.Retrieved, error) {
+				return confmap.NewRetrieved(newConfFromFile(t, filename))
+			})
+			cp, err := NewConfigProvider(ConfigProviderSettings{
+				ResolverSettings: confmap.ResolverSettings{
+					URIs:              []string{uriLocation},
+					ProviderFactories: []confmap.ProviderFactory{fileProvider},
+				},
+			})
+			require.NoError(t, err)
+			factories, err := nopFactories()
+			require.NoError(t, err)
+
+			// Save the previous value of the feature gate and restore it after the test.
+			prev := featuregates.StrictlyTypedInputGate.IsEnabled()
+			defer func() {
+				require.NoError(t, featuregate.GlobalRegistry().Set(featuregates.StrictlyTypedInputID, prev))
+			}()
+
+			// Ensure the error does not appear with the feature gate disabled.
+			require.NoError(t, featuregate.GlobalRegistry().Set(featuregates.StrictlyTypedInputID, false))
+			_, errWeakTypes := cp.Get(context.Background(), factories)
+			if tt.isErrFromStrictTypes {
+				require.Error(t, errWeakTypes)
+				// Ensure coda is **NOT** present.
+				assert.NotContains(t, errWeakTypes.Error(), strictlyTypedMessageCoda)
+			} else {
+				require.NoError(t, errWeakTypes)
+			}
+
+			// Test with the feature gate enabled.
+			require.NoError(t, featuregate.GlobalRegistry().Set(featuregates.StrictlyTypedInputID, true))
+			_, errStrictTypes := cp.Get(context.Background(), factories)
+			require.Error(t, errStrictTypes)
+			if tt.isErrFromStrictTypes {
+				// Ensure coda is **NOT** present.
+				assert.NotContains(t, errStrictTypes.Error(), strictlyTypedMessageCoda)
+			} else {
+				// Ensure coda is present.
+				assert.ErrorContains(t, errStrictTypes, strictlyTypedMessageCoda)
+			}
+		})
+	}
+}

otelcol/testdata/weak-empty-map-to-empty-array.yaml

@@ -0,0 +1,33 @@
+receivers:
+  nop:
+
+processors:
+  nop:
+
+exporters:
+  nop:
+
+extensions:
+  nop:
+
+connectors:
+  nop/con:
+
+service:
+  telemetry:
+    metrics:
+      address: localhost:8888
+  extensions: [nop]
+  pipelines:
+    traces:
+      receivers: [nop]
+      processors: {} # <-- Empty map casted to empty array
+      exporters: [nop, nop/con]
+    metrics:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop]
+    logs:
+      receivers: [nop, nop/con]
+      processors: [nop]
+      exporters: [nop]

otelcol/testdata/weak-implicit-bool-to-int.yaml

@@ -0,0 +1,36 @@
+receivers:
+  nop:
+
+processors:
+  nop:
+
+exporters:
+  nop:
+
+extensions:
+  nop:
+
+connectors:
+  nop/con:
+
+service:
+  telemetry:
+    metrics:
+      address: localhost:8888
+    logs:
+      sampling:
+        initial: true # <-- Implicit cast bool to int
+  extensions: [nop]
+  pipelines:
+    traces:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop, nop/con]
+    metrics:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop]
+    logs:
+      receivers: [nop, nop/con]
+      processors: [nop]
+      exporters: [nop]

otelcol/testdata/weak-implicit-bool-to-string.yaml

@@ -0,0 +1,33 @@
+receivers:
+  nop:
+
+processors:
+  nop:
+
+exporters:
+  nop:
+
+extensions:
+  nop:
+
+connectors:
+  nop/con:
+
+service:
+  telemetry:
+    metrics:
+      address: true # <-- Implicit cast bool to string
+  extensions: [nop]
+  pipelines:
+    traces:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop, nop/con]
+    metrics:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop]
+    logs:
+      receivers: [nop, nop/con]
+      processors: [nop]
+      exporters: [nop]

otelcol/testdata/weak-implicit-int-to-bool.yaml

@@ -0,0 +1,36 @@
+receivers:
+  nop:
+
+processors:
+  nop:
+
+exporters:
+  nop:
+
+extensions:
+  nop:
+
+connectors:
+  nop/con:
+
+service:
+  telemetry:
+    metrics:
+      address: localhost:8888
+    logs:
+      sampling:
+        enabled: 1 # <-- Implicit cast int to bool
+  extensions: [nop]
+  pipelines:
+    traces:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop, nop/con]
+    metrics:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop]
+    logs:
+      receivers: [nop, nop/con]
+      processors: [nop]
+      exporters: [nop]

otelcol/testdata/weak-implicit-int-to-string.yaml

@@ -0,0 +1,33 @@
+receivers:
+  nop:
+
+processors:
+  nop:
+
+exporters:
+  nop:
+
+extensions:
+  nop:
+
+connectors:
+  nop/con:
+
+service:
+  telemetry:
+    metrics:
+      address: 0xdeadbeef # <-- Implicit cast int to string
+  extensions: [nop]
+  pipelines:
+    traces:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop, nop/con]
+    metrics:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop]
+    logs:
+      receivers: [nop, nop/con]
+      processors: [nop]
+      exporters: [nop]

otelcol/testdata/weak-implicit-string-to-bool.yaml

@@ -0,0 +1,36 @@
+receivers:
+  nop:
+
+processors:
+  nop:
+
+exporters:
+  nop:
+
+extensions:
+  nop:
+
+connectors:
+  nop/con:
+
+service:
+  telemetry:
+    metrics:
+      address: localhost:8888
+    logs:
+      sampling:
+        enabled: t # <-- Implicit cast string to bool
+  extensions: [nop]
+  pipelines:
+    traces:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop, nop/con]
+    metrics:
+      receivers: [nop]
+      processors: [nop]
+      exporters: [nop]
+    logs:
+      receivers: [nop, nop/con]
+      processors: [nop]
+      exporters: [nop]