command: New -compact-warnings option

When warnings appear in isolation (not accompanied by an error) it's
reasonable to want to defer resolving them for a while because they are
not actually blocking immediate work.

However, our warning messages tend to be long by default in order to
include all of the necessary context to understand the implications of
the warning, and that can make them overwhelming when combined with other
output.

As a compromise, this adds a new CLI option -compact-warnings which is
supported for all the main operation commands and which uses a more
compact format to print out warnings as long as they aren't also
accompanied by errors.

The default remains unchanged except that the threshold for consolidating
warning messages is reduced to one so that we'll now only show one of
each distinct warning summary.

Full warning messages are always shown if there's at least one error
included in the diagnostic set too, because in that case the warning
message could contain additional context to help understand the error.

command/apply.go

@@ -248,11 +248,15 @@ Usage: terraform apply [options] [DIR-OR-PLAN]
 
 Options:
 
+  -auto-approve          Skip interactive approval of plan before applying.
+
   -backup=path           Path to backup the existing state file before
                          modifying. Defaults to the "-state-out" path with
                          ".backup" extension. Set to "-" to disable backup.
 
-  -auto-approve          Skip interactive approval of plan before applying.
+  -compact-warnings      If Terraform produces any warnings that are not
+                         accompanied by errors, show them in a more compact
+                         form that includes only the summary messages.
 
   -lock=true             Lock the state file when locking is supported.
 

command/format/diagnostic.go

@@ -177,6 +177,51 @@ func Diagnostic(diag tfdiags.Diagnostic, sources map[string][]byte, color *color
 	return buf.String()
 }
 
+// DiagnosticWarningsCompact is an alternative to Diagnostic for when all of
+// the given diagnostics are warnings and we want to show them compactly,
+// with only two lines per warning and excluding all of the detail information.
+//
+// The caller may optionally pre-process the given diagnostics with
+// ConsolidateWarnings, in which case this function will recognize consolidated
+// messages and include an indication that they are consolidated.
+//
+// Do not pass non-warning diagnostics to this function, or the result will
+// be nonsense.
+func DiagnosticWarningsCompact(diags tfdiags.Diagnostics, color *colorstring.Colorize) string {
+	var b strings.Builder
+	b.WriteString(color.Color("[bold][yellow]Warnings:[reset]\n\n"))
+	for _, diag := range diags {
+		sources := tfdiags.WarningGroupSourceRanges(diag)
+		b.WriteString(fmt.Sprintf("- %s\n", diag.Description().Summary))
+		if len(sources) > 0 {
+			mainSource := sources[0]
+			if mainSource.Subject != nil {
+				if len(sources) > 1 {
+					b.WriteString(fmt.Sprintf(
+						"  on %s line %d (and %d more)\n",
+						mainSource.Subject.Filename,
+						mainSource.Subject.Start.Line,
+						len(sources)-1,
+					))
+				} else {
+					b.WriteString(fmt.Sprintf(
+						"  on %s line %d\n",
+						mainSource.Subject.Filename,
+						mainSource.Subject.Start.Line,
+					))
+				}
+			} else if len(sources) > 1 {
+				b.WriteString(fmt.Sprintf(
+					"  (%d occurences of this warning)\n",
+					len(sources),
+				))
+			}
+		}
+	}
+
+	return b.String()
+}
+
 func parseRange(src []byte, rng hcl.Range) (*hcl.File, int) {
 	filename := rng.Filename
 	offset := rng.Start.Byte

command/format/diagnostic_test.go

@@ -0,0 +1,73 @@
+package format
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/hashicorp/hcl/v2"
+	"github.com/mitchellh/colorstring"
+
+	"github.com/hashicorp/terraform/tfdiags"
+)
+
+func TestDiagnosticWarningsCompact(t *testing.T) {
+	var diags tfdiags.Diagnostics
+	diags = diags.Append(tfdiags.SimpleWarning("foo"))
+	diags = diags.Append(tfdiags.SimpleWarning("foo"))
+	diags = diags.Append(tfdiags.SimpleWarning("bar"))
+	diags = diags.Append(&hcl.Diagnostic{
+		Severity: hcl.DiagWarning,
+		Summary:  "source foo",
+		Detail:   "...",
+		Subject: &hcl.Range{
+			Filename: "source.tf",
+			Start:    hcl.Pos{Line: 2, Column: 1, Byte: 5},
+			End:      hcl.Pos{Line: 2, Column: 1, Byte: 5},
+		},
+	})
+	diags = diags.Append(&hcl.Diagnostic{
+		Severity: hcl.DiagWarning,
+		Summary:  "source foo",
+		Detail:   "...",
+		Subject: &hcl.Range{
+			Filename: "source.tf",
+			Start:    hcl.Pos{Line: 3, Column: 1, Byte: 7},
+			End:      hcl.Pos{Line: 3, Column: 1, Byte: 7},
+		},
+	})
+	diags = diags.Append(&hcl.Diagnostic{
+		Severity: hcl.DiagWarning,
+		Summary:  "source bar",
+		Detail:   "...",
+		Subject: &hcl.Range{
+			Filename: "source2.tf",
+			Start:    hcl.Pos{Line: 1, Column: 1, Byte: 1},
+			End:      hcl.Pos{Line: 1, Column: 1, Byte: 1},
+		},
+	})
+
+	// ConsolidateWarnings groups together the ones
+	// that have source location information and that
+	// have the same summary text.
+	diags = diags.ConsolidateWarnings(1)
+
+	// A zero-value Colorize just passes all the formatting
+	// codes back to us, so we can test them literally.
+	got := DiagnosticWarningsCompact(diags, &colorstring.Colorize{})
+	want := `[bold][yellow]Warnings:[reset]
+
+- foo
+- foo
+- bar
+- source foo
+  on source.tf line 2 (and 1 more)
+- source bar
+  on source2.tf line 1
+`
+	if got != want {
+		t.Errorf(
+			"wrong result\ngot:\n%s\n\nwant:\n%s\n\ndiff:\n%s",
+			got, want, cmp.Diff(want, got),
+		)
+	}
+}

command/meta.go

@@ -157,6 +157,9 @@ type Meta struct {
 	// init.
 	//
 	// reconfigure forces init to ignore any stored configuration.
+	//
+	// compactWarnings (-compact-warnings) selects a more compact presentation
+	// of warnings in the output when they are not accompanied by errors.
 	statePath        string
 	stateOutPath     string
 	backupPath       string
@@ -166,6 +169,7 @@ type Meta struct {
 	stateLockTimeout time.Duration
 	forceInitCopy    bool
 	reconfigure      bool
+	compactWarnings  bool
 
 	// Used with the import command to allow import of state when no matching config exists.
 	allowMissingConfig bool
@@ -377,6 +381,7 @@ func (m *Meta) extendedFlagSet(n string) *flag.FlagSet {
 
 	f.BoolVar(&m.input, "input", true, "input")
 	f.Var((*FlagTargetSlice)(&m.targets), "target", "resource to target")
+	f.BoolVar(&m.compactWarnings, "compact-warnings", false, "use compact warnings")
 
 	if m.variableArgs.items == nil {
 		m.variableArgs = newRawFlags("-var")
@@ -480,8 +485,33 @@ func (m *Meta) showDiagnostics(vals ...interface{}) {
 	diags = diags.Append(vals...)
 	diags.Sort()
 
+	if len(diags) == 0 {
+		return
+	}
+
+	diags = diags.ConsolidateWarnings(1)
+
 	// Since warning messages are generally competing
-	diags = diags.ConsolidateWarnings()
+	if m.compactWarnings {
+		// If the user selected compact warnings and all of the diagnostics are
+		// warnings then we'll use a more compact representation of the warnings
+		// that only includes their summaries.
+		// We show full warnings if there are also errors, because a warning
+		// can sometimes serve as good context for a subsequent error.
+		useCompact := true
+		for _, diag := range diags {
+			if diag.Severity() != tfdiags.Warning {
+				useCompact = false
+				break
+			}
+		}
+		if useCompact {
+			msg := format.DiagnosticWarningsCompact(diags, m.Colorize())
+			msg = "\n" + msg + "\nTo see the full warning notes, run Terraform without -compact-warnings.\n"
+			m.Ui.Warn(msg)
+			return
+		}
+	}
 
 	for _, diag := range diags {
 		// TODO: Actually measure the terminal width and pass it here.

command/plan.go

@@ -201,6 +201,10 @@ Usage: terraform plan [options] [DIR]
 
 Options:
 
+  -compact-warnings   If Terraform produces any warnings that are not
+                      accompanied by errors, show them in a more compact form
+                      that includes only the summary messages.
+
   -destroy            If set, a plan will be generated to destroy all resources
                       managed by the given configuration and state.
 

command/refresh.go

@@ -124,6 +124,10 @@ Options:
                       modifying. Defaults to the "-state-out" path with
                       ".backup" extension. Set to "-" to disable backup.
 
+  -compact-warnings   If Terraform produces any warnings that are not
+                      accompanied by errors, show them in a more compact form
+                      that includes only the summary messages.
+
   -input=true         Ask for input for variables if not directly set.
 
   -lock=true          Lock the state file when locking is supported.

tfdiags/consolidate_warnings.go

@@ -15,12 +15,9 @@ import "fmt"
 // The returned slice always has a separate backing array from the reciever,
 // but some diagnostic values themselves might be shared.
 //
-// The definition of "unreasonable" may change in future releases.
-func (diags Diagnostics) ConsolidateWarnings() Diagnostics {
-	// We'll start grouping when there are more than this number of warnings
-	// with the same summary.
-	const unreasonableThreshold = 2
-
+// The definition of "unreasonable" is given as the threshold argument. At most
+// that many warnings with the same summary will be shown.
+func (diags Diagnostics) ConsolidateWarnings(threshold int) Diagnostics {
 	if len(diags) == 0 {
 		return nil
 	}
@@ -55,7 +52,7 @@ func (diags Diagnostics) ConsolidateWarnings() Diagnostics {
 		}
 
 		warningStats[summary]++
-		if warningStats[summary] == unreasonableThreshold {
+		if warningStats[summary] == threshold {
 			// Initially creating the group doesn't really change anything
 			// visibly in the result, since a group with only one warning
 			// is just a passthrough anyway, but once we do this any additional
@@ -128,3 +125,22 @@ func (wg *warningGroup) Append(diag Diagnostic) {
 	}
 	wg.Warnings = append(wg.Warnings, diag)
 }
+
+// WarningGroupSourceRanges can be used in conjunction with
+// Diagnostics.ConsolidateWarnings to recover the full set of original source
+// locations from a consolidated warning.
+//
+// For convenience, this function accepts any diagnostic and will just return
+// the single Source value from any diagnostic that isn't a warning group.
+func WarningGroupSourceRanges(diag Diagnostic) []Source {
+	wg, ok := diag.(*warningGroup)
+	if !ok {
+		return []Source{diag.Source()}
+	}
+
+	ret := make([]Source, len(wg.Warnings))
+	for i, wrappedDiag := range wg.Warnings {
+		ret[i] = wrappedDiag.Source()
+	}
+	return ret
+}

tfdiags/consolidate_warnings_test.go

@@ -53,7 +53,7 @@ func TestConsolidateWarnings(t *testing.T) {
 
 	// We're using ForRPC here to force the diagnostics to be of a consistent
 	// type that we can easily assert against below.
-	got := diags.ConsolidateWarnings().ForRPC()
+	got := diags.ConsolidateWarnings(2).ForRPC()
 	want := Diagnostics{
 		// First set
 		&rpcFriendlyDiag{

website/docs/commands/apply.html.markdown

@@ -27,6 +27,10 @@ The command-line flags are all optional. The list of available flags are:
 * `-backup=path` - Path to the backup file. Defaults to `-state-out` with
   the ".backup" extension. Disabled by setting to "-".
 
+* `-compact-warnings` - If Terraform produces any warnings that are not
+  accompanied by errors, show them in a more compact form that includes only
+  the summary messages.
+
 * `-lock=true` - Lock the state file when locking is supported.
 
 * `-lock-timeout=0s` - Duration to retry a state lock.

website/docs/commands/plan.html.markdown

@@ -37,6 +37,10 @@ inspect a planfile.
 
 The command-line flags are all optional. The list of available flags are:
 
+* `-compact-warnings` - If Terraform produces any warnings that are not
+  accompanied by errors, show them in a more compact form that includes only
+  the summary messages.
+
 * `-destroy` - If set, generates a plan to destroy all the known resources.
 
 * `-detailed-exitcode` - Return a detailed exit code when the command exits.

website/docs/commands/refresh.html.markdown

@@ -29,6 +29,10 @@ The command-line flags are all optional. The list of available flags are:
 * `-backup=path` - Path to the backup file. Defaults to `-state-out` with
   the ".backup" extension. Disabled by setting to "-".
 
+* `-compact-warnings` - If Terraform produces any warnings that are not
+  accompanied by errors, show them in a more compact form that includes only
+  the summary messages.
+
 * `-input=true` - Ask for input for variables if not directly set.
 
 * `-lock=true` - Lock the state file when locking is supported.